A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
Periodic table class 10 NCERT CHEMISTRY MCQ & SAQ
Periodic table class 10 NCERT CHEMISTRY NCERT SOLUTION
1. Did Dobereiner's triads also exist in the columns of Newlands' Octaves? Compare and find out.
Answer
Yes, Dobereiner's triads also exist in the columns of Newlands' Octaves. One such column is Li, K, Na.
2. What were the limitations of Dobereiner's classification?
Answer
Limitation of Dobereiner's classification:
All known elements could not be classified into groups of triads on the basis of their properties.
3. What were the limitations of Newlands' Law of Octaves?
Answer
Limitations of Newlands' law of octaves:
→ It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
→ Those elements that were discovered after Newlands' octaves did not follow the law of octaves.
→ The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
→ Placing iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.
Page No: 85
1. Use Mendeleev's Periodic Table to predict the formula for the oxides of the following elements:
K, C, Al, Si, Ba.
Answer
K is in group 1. Therefore, the oxide will be K2O.
C is in group 4. Therefore, the oxide will be CO2.
Al is in group 3. Therefore, the oxide will be Al2O3.
Si is in group 4. Therefore, the oxide will be SiO2.
Ba is in group 2. Therefore, the oxide will be BaO.
2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Answer
Scandium and germanium.
3. What were the criteria used by Mendeleev in creating his Periodic Table?
Answer
Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.
4. Why do you think the noble gasses are placed in a separate group?
Answer
Noble gasses are inert elements. Their properties are different from all other elements. Therefore, the noble gasses are placed in a separate group.
Page No: 90
1. How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?
Answer
Various anomalies of Mendeleev’s Periodic Table removed as follows in the Modern Periodic Table:
→ Elements are arranged in the increasing order of their atomic number in the Modern Periodic Table, thus there was no need for keeping more than one element in one slot.
→ In the Modern Periodic Table there was no problem of the place of isotopes, as isotopes have the same atomic mass with different atomic numbers.
→ Elements having the same valence electron are kept in the same group.
→ Elements having the same number of shells were put under the same period.
→ Position of hydrogen becomes clarified as it is kept in the group with the elements of same valence electrons.
2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Answer
Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is the same in all these three elements and since chemical properties are due to valence electrons, they show the same chemical reactions.
3. Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.
Answer
(a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.
4. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
Answer
(a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.
(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.
5. In the Modern Periodic Table, which are the metals among the first ten elements?
Answer
Among the first ten elements, lithium (Li) and beryllium (Be) are metals.
6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?
Answer
Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.
Page No: 91
Exercise
1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
► (c) The atoms lose their electrons more easily.
2. Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na
(b) Mg
(c) Al
(d) Si
► (b) Mg
3. Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?
Answer
(a) Neon
(b) Magnesium
(c) Silicon
(d) Boron
(e) Carbon
4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer
(a) Valency equal to 3.
(b) Valency equal to 1.
5. An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)
N(7) F(9) P(15) Ar(18)
Answer
(a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration as 2, 7.
Page No: 92
6. The position of three elements A, B and C in the Periodic Table are shown below -
(a) State whether A is a metal or nonmetal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
Answer
(a) A is a non-metal.
(b) C is less reactive than A, as reactivity decreases down the group in halogens.
(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
(d) A will form an anion as it accepts an electron to complete its octet.
7. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Answer
Nitrogen (7): 2, 5
Phosphorus (15): 2, 8, 5
Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.
8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer
In the modern periodic table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same.
Elements across a period show an increase in the number of valence electrons.
9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?
Answer
The element with atomic number 12 has the same chemical properties as that of calcium. This is because both of them have the same number of valence electrons (2).
10. Compare and contrast the arrangement of elements in Mendeleev's Periodic Table and the Modern Periodic Table.
Answer
Periodic table class 10 NCERT CHEMISTRY MCQ
Question : Which of the given elements A, B , C, D and E with atomic numbers 2, 4, 8, 10 and 18 respectively belong to the same period?
a) B,C,D
b) A, B, C
c) A,D,E
d) B,D,E
Answer : B,C,D
Question : Which of the following elements would accept an electron readily:
a) Cl
b) F
c) Br
d) I
Answer : Cl
Question : Which of the following elements would lose an electron easily:
a) K
b) Na
c) Ca
d) Mg
Answer : K
Question : An element has 13 protons. The group and period to which it belongs:
a) 3rd period and 13th group
b) 2nd period and 13th group
c) 3rd period and 3rd group
d) 2nd period and 3rd group
Answer : 3rd period and 13th group
Question : The most metallic element in the fourth period is:
a) K
b) Ca
c) S
d) P
Answer : K
Question : Which of the following has most non metallic character:
a) F
b) N
c) C
d) O
Answer : F
Question : The lightest metal is :
a) Li
b) Na
c) K
d) Mg
Answer : Li
Question : Which of the following is the correct order of size:
a) F< Cl< Br< I
b) Cl< F< Br< I
c) I<br< cl
d) Br< I< Cl< F
Answer : F< Cl< Br< I
Question : Which of the given elements A, B , C, D and E with atomic numbers 2, 4, 8, 10 and 18 respectively belong to the same period?
a) B,C,D
b) A, B, C
c) A,D,E
d) B,D,E
Answer : B,C,D
Question : Where would you locate an element with electronic configuration 2, 8,7 in the modern periodic table?
a) Group7 and period 3
b) Group 7 and period 2
c) Group 17 and period 3
d) Group17 and period 3
Answer : Group7 and period 3
Question : Which of the following is the correct order of size:
a) I- >I > I+
b) I+ >I- > I
c) I >I+ > I
d) I >I- > I+
Answer : I- >I > I+
Question : Which of the following hydroxides are most basic:
a) Ba(OH)2
b) Be(OH)2
c) Mg(OH)2
d) Ca(OH)2
Answer : Ba(OH)2
Question : Which of the following are characteristics of isotopes of an element?
a) Isotopes of an element have same atomic masses
b) Isotopes of an element have same atomic number
c) Isotopes of an element show same physical properties
d) Isotopes of an element have same chemical properties
a) B and c
b) A, c, d
c) B, c, d
d) B and d
Answer : B and c
Question : Which amongst the following represents the correct order of decreasing metallic character of elements Na, Si, Cl, Mg, Al
a) Na> Mg> Al> Si> Cl
b) Cl> Si> Al> Mg> Na
c) Na> Si> Mg> Al> Cl
d) Al> Na> Si> Cl> Mg
Answer : Na> Mg> Al> Si> Cl
Question : Which of the following will form acidic oxide? An element with atomic number:
a) 7
b) 11
c) 21
d) 19
Answer : 7
Question : Elements with atomic number 15 and mass number 31 is present in:
a) Group15 and period 3
b) Group 5 and period 4
c) Group5 and period 3
d) Group15 and period 4
Answer : Group15 and period 3
Question : The pairs of elements with the following atomic numbers have the same chemical properties:
a) 3 & 11
b) 13 & 12
c) 4 & 24
d) 2 & 1
Answer : 3 & 11
Question : The number of elements present in the 2nd, 3rd, 4th and 5th periods of the modern periodic table are:
a) 8,8,18,32
b) 2,8,8,18
c) 8,8,18, 18
d) 8,18,18,32
Answer : 8,8,18,32
Question : The longest and the shortest periods are:
a) 6 &1
b) 1&6
c) 2&6
d) 1&7
Answer : 6 & 1
Question : The period that contains only gaseous elements are:
a) 1
b) 2
c) 3
d) 4
Answer : 1
Question : The period that contains only gaseous elements are:
a) 1
b) 2
c) 3
d) 4
Answer : A
Question : The longest and the shortest periods are:
a) 1&6
b) 2&6
c) 6 &1
d) 1&7
Answer : C
Question : The number of elements present in the 2nd, 3rd, 4th and 5th periods of the modern periodic table are:
a) 2,8,8,18
b) 8,8,18,32
c) 8,8,18, 18
d) 8,18,18,32
Answer : B
Question : The pairs of elements with the following atomic numbers have the same chemical properties:
a) 13 & 12
b) 3 &11
c) 4&24
d) 2 &1
Answer : B
Question : Elements with atomic number 15 and mass number 31 is present in:
a) Group 5 and period 4
b) Group5 and period 3
c) Group15 and period 3
d) Group15 and period 4
Answer : C
Question : Which of the following will form acidic oxide? An element with atomic number:
a) 7
b) 11
c) 21
d) 19
Answer : A
Question : Which amongst the following represents the correct order of decreasing metallic character of elements Na, Si, Cl, Mg, Al
a) Cl> Si> Al> Mg> Na
b) Na> Mg> Al> Si> Cl
c) Na> Si> Mg> Al> Cl
d) Al> Na> Si> Cl> Mg
Answer : B
Question : Which of the following are characteristics of isotopes of an element?
a) Isotopes of an element have same atomic masses
b) Isotopes of an element have same atomic number
c) Isotopes of an element show same physical properties
d) Isotopes of an element have same chemical properties
i. A, c, d
ii. B, c, d
iii. B and c
iv. B and d
Answer : C
Question : Where would you locate an element with electronic configuration 2, 8,7 in the modern periodic table?
a) Group 7 and period 2
b) Group7 and period 3
c) Group 17 and period 3
d) Group17 and period 3
Answer : B
Question : Which of the given elements A, B , C, D and E with atomic numbers 2, 4, 8, 10 and 18 respectively belong to the same period?
a) A, B, C
b) B,C,D
c) A,D,E
d) B,D,E
Answer : B
Question : Which of the following hydroxides are most basic:
a) Be(OH)2
b) Mg(OH)2
c) Ca(OH)2
d) Ba(OH)2
Answer : D
Question : Which of the following is the correct order of size:
a) I+ >I- > I
b) I- >I > I+
c) I >I+ > I
d) I >I- > I+
Answer : B
Question : Which of the following is the correct order of size:
a) Cl< F< Br< I
b) F< Cl< Br< I
c) I<Br< Cl< F
d) Br< I< Cl< F
Answer : B
Question : The lightest metal is :
a) Li b) Na c) K d) Mg
Answer : A
Question : Which of the following has most non metallic character:
a) N b) C c) O d) F
Answer : D
Question : The most metallic element in the fourth period is:
a) Ca b) K c) S d) P
Answer : B
Question : An element has 13 protons. The group and period to which it belongs:
a) 3rd period and 13th group
b) 2nd period and 13th group
c) 3rd period and 3rd group
d) 2nd period and 3rd group
Answer : A
Question : Which of the following elements would lose an electron easily:
a) K b) Na c) Ca d) Mg
Answer : A
Question : Which of the following elements would accept an electron readily:
a) F b) Cl c) Br d) I
Answer : B
1. The most distinctive property of the noble gasses is that they are:
(a) Unreactive
(b) Radioactive
(c) Metalloid
(d) Metallic
► (a) Unreactive
2. According to IUPAC recommendations, the number of groups in the long form of the periodic table is:
(a) 7
(b) 8
(c) 16
(d) 18
► (d) 18
3. Up to which element, the Law of Octaves was found applicable?
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium
► (b) Calcium
4. At the time of Mendeleev, the number of elements known was
(a) 63
(b) 65
(c) 62
(d) 64
► (a) 63
5. As we move from left to right in a period in modern periodic table, Atomic sizes of the elements generally
(a) increase
(b) decrease
(c) remain same
(d) approach zero
► (b) decrease
6. Newlands relation is called
(a) Musical Law
(b) Law of Octaves
(c) Periodic Law
(d) Atomic Mass Law
► (b) Law of Octaves
7. The arrangement of elements in the Modern Periodic Table is based on their
(a) increasing atomic mass in the period
(b) increasing atomic number in the horizontal rows
(c) increasing atomic number in the vertical columns
(d) increasing atomic mass in the group
► (b) increasing atomic number in the horizontal rows
8. An atom of an element has the electronic confi-guration 2,8,2. To which group does it belong?
(a) 4th group
(b) 6th group
(c) 3rd group
(d) 2nd group
► (d) 2nd group
9. Carbon belongs to the second period and Group 14. Silicon belongs to the third period and Group 14. If atomic number of carbon is 6, the atomic number of silicon is
(a) 7
(b) 14
(c) 24
(d) 16
► (b) 14
10. Where would you locate the element with electronic configuration 2, 8 in the Modern Periodic Table?
(a) Group 8
(b) Group 2
(c) Group 18
(d) Group 10
► (c) Group 18
11. In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the Periodic Table later?
(a) Chlorine
(b) Silicon
(c) Oxygen
(d) Germanium
► (d) Germanium
12. What is the atomic number of elements of period 3 and group 17 of the Periodic Table?
(a) 10
(b) 4
(c) 17
(d) 21
► (c) 17
13. The law of the modern periodic table was proposed by:
(a) H.G.J Moselly
(b) Dobereincer
(c) D.I. Mendeleev
(d) Newlands
► H.G.J Moselly
14. Pick out the chemically most reactive elements from the given triads.
Li, Na, K F, Cl, Br
(a) Li and F
(b) Li and Br
(c) K and F
(d) K and Br
► (c) K and F
15. The elements A, B and C belong to groups 1, 14 and 17 respectively of the Periodic Table. Which two elements will form ionic compounds?
(a) A and B
(b) A and C
(c) B and C
(d) None
► (b) A and C
16. Element X forms a chloride with the formula XCl2, which is a solid with high melting point. X would most likely be:
(a) Si
(b) Al
(c) Na
(d) Mg
► (d) Mg
17. Which one of the following statements is not correct about the trends in the properties of the elements of a period on going from left to right?
(a) The oxides become more acidic
(b) The elements become less metallic
(c) There is an increase in the number of valence electrons
(d) The atoms lose their electrons more easily
► (d) The atoms lose their electrons more easily
18. Dobereiner’s triad arranged the elements with similar properties into:
(a) Periods
(b) Groups
(c) Both period and group
(d) None of these
► (b) Groups
19. Name the neutral atom in the Periodic Table which has the same number of electrons as K+ and Cl-.
(a) Helium
(b) Argon
(c) Neon
(d) Krypton
► (b) Argon
20. Which of the following is the outermost shell for elements of the second period?
(a) K shell
(b) L shell
(c) M shell
(d) N shell
► (b) L shell
21. An element X has mass number 40 and contains 21 neutrons in its atom. To which group of the Periodic Table does it belong?
(a) Group 1
(b) Group 4
(c) Group 2
(d) Group 3
► (a) Group 1
22. An element ‘A’ belongs to the third period and group 16 of the Periodic Table. Find out the valency of A.
(a) Valency = 6
(b) Valency = 2
(c) Valency = 1
(d) Valency = 3
► (b) Valency = 2
23. How many elements are placed in lanthanide and actinide series?
(a) 57, 89
(b) 14, 14
(c) 89, 57
(d) 14, 16
► (b) 14, 14
24. An element X combines with oxygen to form an oxide XO. This oxide is electrically conducting. Write the formula of the compound formed when X reacts with chlorine.
(a) XCl3
(b) XCl
(c) XCl2
(d) XCl5
► (c) XCl2
25. Which of the following elements of noble gasses participate in chemical reaction?
(a) Kr, Rn
(b) He, Kr
(c) Rn, He
(d) He, Ne
► (a) Kr, Rn
26. Which one of the following statements is not correct about the trends in the properties of the elements of a group on going down in a group?
(a) The chemical reactivity of metals increases.
(b) The metallic character of elements increases.
(c) The size of the atom increases.
(d) The valence electrons increase.
► (d) The valence electrons increase.
27. The element which has least tendency to lose electron is
(a) H
(b) Li
(c) He
(d) Ne
► (c) He
28. An element has 12 protons. The group and period to which this element belongs to is
(a) 2nd group, 3rd period
(b) 2nd group, 2nd period
(c) 3rd group, 2nd period
(d) 3rd group, 3rd period
► (a) 2nd group, 3rd period
29. The metal which is hard and has high melting point and used in filaments of electrical bulbs is
(a) Ni
(b) Fe
(c) Pt
(d) W
► (d) W
30. The non-metals are present:
(a) On the right hand side of the periodic table.
(b) In the middle of the periodic table.
(c) In the center of the periodic table.
(d) On the left hand side of the periodic table.
► (a) On the right hand side of the periodic table.
31. Mendeleev’s classification was based on _______ .
(a) Increasing atomic mass
(b) Decreasing atomic number
(c) Increasing atomic number
(d) Decreasing atomic mass
► (a) Increasing atomic mass
32. Which of the following set of elements is written in order of their increasing metallic character?
(a) Na Li K
(b) C Q N
(c) Mg Al Si
(d) Be Mg Ca
► (d) Be Mg Ca
33. The elements of group 16 are called
(a) Chalcogens
(b) Halogens
(c) Pnicogens
(d) Noble gasses
► (a) Chalcogens
34. In Mendeleev’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later ? [NCERT Exemplar Problems]
(a) Germanium
(b) Chlorine
(c) Oxygen
(d) Silicon
► (a) Germanium
35. Nitrogen and phosphorus belong to the group 15 of the periodic table. Which of these will be more electronegative?
(a) Phosphorus
(b) Both are equally electronegative
(c) Nitrogen
(d) None of these
► (c) Nitrogen
36. Modern Periodic law is based upon:
(a) Number of neutrons
(b) Number of electron
(c) Atomic number
(d) Atomic mass
► (c) Atomic number
37. Which one of the following elements exhibit the maximum number of valence electrons?
(a) Na
(b) Al
(c) Si
(d) P
► (d) P
38. Which of the following statements about the Modern Periodic Table is correct?
(a) It has 18 horizontal rows known as Periods
(b) It has 7 vertical columns known as Periods
(c) It has 18 vertical columns known as Groups
(d) It has 7 horizontal rows known as Groups
► (c) It has 18 vertical columns known as Groups
39. Upto which element, the Law of Octaves was found to be applicable:
(a) Oxygen
(b) Calcium
(c) Cobalt
(d) Potassium
► (b) Calcium
40. Which of the following is most reactive
(a) F2
(b) Cl2
(c) Br2
(d) I2
► (a) F2
41. Chlorine (17) belongs to which group and period
(a) 7, 3
(b) 17, 3
(c) 1, 3
(d) 16, 3
► (b) 17, 3
42. An element has an atomic number of 15 with which of the following elements will it show similar chemical properties.
(a) Be (4)
(b) Ne (10)
(c) N (7)
(d) O (8)
► (c) N (7)
43. Which of the following sets of elements do not belong to the same group?
(a) F, Cl, Br
(b) Na, K, Rb
(c) P, S, Cl
(d) C, Si, Ge
► (c) P, S, Cl
44. What is the basis of the long form of the periodic table?
(a) Atomic mass
(b) Atomic number
(c) Atomic size
(d) Metallic and Non-metallic character
► (b) Atomic number
45. Silicon(14) belongs to class of
(a) Metal
(b) Non-metal
(c) Metalloids
(d) Ionic compound
► (c) Metalloids
46. Which of the following is most reactive
(a) Li
(b) H
(c) Na
(d) K
► (d) K
47. The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong?
(a) Metal
(b) Metalloid
(c) Non-metal
(d) Left-hand side element
► (b) Metalloid
Periodic table class 10 NCERT CHEMISTRY SAQ
(a) What is meant by periodicity
in properties of elements with reference to the periodic table?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period? Why?
Answer.
(a) The repetition of same properties after a definite interval is called periodicity in properties.
(b) It is because they have the same valence electrons and therefore, have similar properties.
(c) Tendency to gain electrons increases from left to right in a period because atomic size goes on decreasing and effective nuclear charge increases.
The elements of the second period of the Periodic Table are given below:
Li Be B C N O F
(a) Give reason to explain why atomic radii decrease from Li to F.
(b) Identify the most
(i) metallic and
(ii)non-metallic element.
Answer.
(a) It is because nuclear charge increases due to increase in atomic number, therefore, force of attraction between nucleus and valence electrons increases, i.e. effective nuclear charge increases, hence atomic radii decrease from Li to F.
(b) (i) Most metallic element is ‘Li’ as it
can lose electrons easily due to larger atomic size.
(ii) Most non-metallic element is ‘F’ because it can gain electrons easily due to the smallest atomic size.
Q.1. An element ‘X’ with electronic configuration (2, 8, 2) combines separately with two radicals, (NO3)- and (SO4)2-.
(i) Is ‘X’ a metal or a non-metal? Write the nature of its oxide
(ii) Write the formula of the compounds of ‘X’ formed by the combination of these radicals. Are these compounds covalent or electrovalent? [AI 2017C]
Ans. (i) X is a metal as it can lose 2 electrons from its valence shell. It forms basic oxides.
(ii) X(NO3)2, XSO4. ‘X’ will form electrovalent compounds.
Q.2. Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius, and (c) maximum chemical reactivity? Justify your answer stating the reason for each. [AI 2017]
Ans. (a) Al has the highest valency equal to 3 because its electronic configuration is 2, 8, 3. It can lose 3 electrons to become stable.
(b) Na has the largest atomic size because it has the least effective nuclear charge as the atomic radius decreases when we move left to right in a period.
(c) Na is most reactive due to the largest atomic size, it can lose electrons easily due to the noble gas configuration.
Q.3. Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table.
How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Given reason in support of your answer in the above two cases. [Delhi 2017]
Ans. The vertical columns of the periodic table are called groups.
The horizontal rows are called periods.
Metallic character: It increases down the group in a vertical column.
Reason: Effective nuclear charge decreases, as tendency to lose electrons increases on moving down the group because the attraction between the nucleus and the valence electron decreases.
Atomic radius: It decreases along left to right in a period.
Reason: It is because the number of shells remains the same. Effective nuclear charge increases due to addition of one proton and one electron successively.
Q.4. An element ‘M’ has atomic number 12.
(i) Write its electronic configuration and valency.
(ii) Is ‘M’ a metal or nonmetal? Give reason in support of your answer.
(iii) Write the formula and nature (acidic/basic) of the oxide of M. [Delhi 2017C]
Ans. (i) Its electronic configuration 2, 8,2 and valency is 2.
(ii) ‘M’ is a metal as it can lose its 2 valence electrons to achieve the noble gas configuration.
(iii) The formula and nature of the oxide of M is MO and it forms basic oxide.
Q.5. An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reason: Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q. [Delhi 2017]
Ans. P(20) 2, 8, 8, 2 Valency 2
Q(17) 2, 8, 7 Valency 1
Element P has 2 valence electrons and 4 shells, therefore, it belongs to group 2 and 4th period of periodic table Element Q has 7 valence electrons and 3 shells, therefore, it belongs to group 17 and 3rd period of periodic table.
The compound formed between P and Q will have formula PO2
Q.6. The atomic number of an element is 20.
(a) Write its electronic configuration and determine its valency.
(b) Is it a metal or a non-metal?
(c) Write the formula of its chloride.
(d) Is it more reactive or less reactive than Mg (atomic number 12)? Give reason for your answer. [Foreign 2017]
Ans. (a) Electronic configuration: 2, 8, 8, 2; valency: 2.
(b) It is a metal.
(c) XCl2 or CaCl2
(d) It is more reactive than Mg because it is larger in size, therefore has more tendency to lose electrons due to less effective nuclear charge.
Q.7. (a) Name the metals among the first five elements of the Modern Periodic Table.
(b) Write their chemical symbols.
(c) Write the formula of their oxides. [CBSE 2016]
Ans. (a) Lithium and Beryllium
(b) Li and Be
(c) Li2O and BeO are formulas of their oxides.
Q.8. Two elements X and Y have atomic number 11 and 16 respectively.
(i) Write the electronic configuration of both.
(ii) Which type of bond will they form?
(iii) Write the formula of the compound formed by their combination (in terms of X and Y). [CBSE 2016]
Ans.
(i) Electronic configuration of X (2, 8, 1) and Y(2,8,6)
(ii) They will form ionic bond
(iii) X2Y is the formula of compound formed.
Q.9. An element ‘X’ belongs to the 3rd period and group 16 of the Modern Periodic Table.
(а) Determine the number of valence electrons and the valency of ‘X’.
(b) Molecular formula of the compound when ‘X’ reacts with hydrogen and writes its electron dot structure.
(c) Name the element ‘X’ and state whether it is metallic or non-metallic. [Al 2016]
Ans. (a) ‘X’ has electronic configuration 2, 8, 6
∴ It has 6 valence electrons, therefore, it valency equal to 2.
(b) H2X ( H1 and X2-)
(c) ‘X’ is Sulfur. It is non-metallic.
Q.10. An element ‘X’ (Atomic number 20) burns in presence of oxygen to form a basic oxide.
(a) Identify the element and write its electronic configuration.
(b) State its group number and period number in the Modern Periodic Table.
(c) Write a balanced chemical equation for the reaction when this oxide is dissolved in water. [CBSE 2016]
Ans. (a) The element is calcium. Its electronic configuration 2, 8, 8, 2.
(b) It belongs to group 2 and 4th period.
(c)
Q.11. Out of the following elements
H (l); Be(4); N a ( l l ) ; Mg(12)
(a) Write the pair elements having similar chemical properties.
(b) State the group number of each pair.
(c) Name one other element belonging to each of these groups. [CBSE 2016]
Ans. (a) Be (4) and Mg (12)
H (1) and Li (3)
(b) 1st pair belongs to Group 2nd pair belongs to Group 1.
(c) Calcium belongs to Group 2, sodium belongs to Group 1.
Q.12. An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’. [AI 2016]
Ans. ‘X’ has mass number = 35
Number of neutrons =18
Number of protons = Atomic number = 35-18 = 17
Electronic configuration 2, 8, 7
It belongs to group 17 and 3rd period.
Its valency is equal to 1.
Q.13. An element ‘M’ with electronic configuration (2, 8, 2) combines separately with (NO4)3-, (SO4)2- and (PO4)3- radicals. Write the formula of the three compounds so formed. To which group and period of the Modern Periodic Table does the element ‘M’ belong? Will ‘M’ form covalent or ionic compounds? Give reason to justify your answer. [Delhi 2016]
Ans. M(NO3)2
‘M’ or Mg has 2 valence electrons, therefore, its valency is equal to 2.
MSO4, M3(PO4)2
It belongs to the group 2nd and 3rd period of the Modem Periodic Table.
‘M’ will form ionic compounds because it can lose 2 electrons easily to become stable.
Q.14. Which has a larger atomic radius Ca (20) or K (19). [CBSE 2016]
Ans. K (19) has a larger atomic radius due to less effective number charge.
Q.15. Out of Li and K, which have stronger metallic character and why? [CBSE 2016]
Ans. K because it has a larger size and more tendency to lose electrons.
Q.16. An element has atomic number 17 to which group and period does it belong. [CBSE 2016]
Ans. Its electronic configuration is 2, 8, 7. It belongs to group 17 because it has 7 valence electrons. It belongs to the 3rd period because it has 3 shells.
Q.17. Calcium is an element with atomic number 20. Stating reason answer each of the following questions :
(i) Is calcium a metal or nonmetal?
(ii) Will its atomic radius be larger or smaller than that of potassium with atomic number 19?
(iii) Write the formula of its oxide. [CBSE 2016]
Ans. (i) Calcium is a metal.
The oxide of calcium viz., CaO is a basic oxide because it dissolves in water to give a base (alkali).
2Ca + O2 → 2CaO
(ii) Atomic radius of Ca is smaller than that of K. This is because the next electron enters the same orbit as that of the last electron of K.
Electronic configuration of K : 2, 8, 8, 1
Electronic configuration of Ca : 2, 8, 8, 2
And because of the increased nuclear charge, the electrons in the last orbit are attracted with a greater force resulting in the decrease of atomic radius.
(iii) CaO is the formula of oxide of calcium.
Q.18. The elements 4Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:
(a) In which group should they be?
(A) Which one of them is least reactive?
(c) Which one of them has the largest atomic size? [AI 2015, 2014]
Ans. (a) They belong to group 2, since they have 2 valence electrons.
(b) ‘Be’ is least reactive because of more effective nucleus charge due to smaller size and least tendency to lose electrons.
(c) ‘Ca’ has the largest atomic size due to the presence of 4 shells.
Q.19. Taking the example of an element of atomic number 16, explain how the electronic configuration of the atom of an element relates to its position in the Modern Periodic Table and how valency of an element is calculated on the basis of its atomic number. [Al 2015]
Ans. S(16) has electronic configuration 2, 8, 6. It has 6 valence electrons. It belongs to Group 16. It has three shells, therefore, it belongs to the 3rd period. It has 6 valence electrons. It can gain 2 electrons to complete its octet, therefore, its valency is equal to 2.
Q.20. Given below are some elements of the Modern Periodic Table. Atomic number of the element is given in the parentheses:
A(4), B(9), C(14), D(19), E(20)
(a) Select the element that has one electron in the outermost shell. Also write the electronic configuration of this element.
(b) Which two elements amongst these belong to the same group? Give reason for your answer.
(c) Which two elements amongst these belong to the same period? Which one of the two has a bigger atomic radius? [Al 2015]
Ans. (a) D(19) = 2, 8, 8, 1
It has one valence electron.
(b) ‘A- and ‘E’ belong to the same group because they have the same number of valence electrons.
(c) ‘A’ and ‘B’ belong to the same period as they have the same number of shells. A(4) = 2,2; B(9) = 2, 7. ‘A’ has a bigger atomic size due to less effective nuclear charge.
Q.21. Na, Mg and Al are the elements of the same period of the Modern Periodic Table having one, two and three valence electrons respectively. Which of these elements (i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating the reason for each case. [Delhi 2015]
Ans. (i) Na has the largest atomic radius because it has 11 protons and 11 electrons and the least effective nuclear charge among these elements.
(ii) Al is least reactive because it is smallest in size, therefore, has the most effective nuclear charge and the least tendency to lose electrons.
Q.22. Two elements ‘P’ and ‘Q’ belong to the same period of the modern periodic table and are in Group-1 and Group-2 respectively. Compare their following characteristics in tabular form:
(a) The number of electrons in their atoms
(b) The sizes of their atoms
(c) Their metallic characters
(d) Their tendencies to lose electrons
(e) The formula of their oxides
(f) The formula of their chlorides [Al 2015]
Ans.
Q.23. How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move :
(a) down a group and
(b) from left to right in a period. [CBSE 2015]
Ans. There are 18 groups and 7 periods in the modern periodic table.
(a) On moving down a group, the atomic size increases and metallic character also increases.
(b) On moving from left to right in a period, the atomic size decreases and the metallic character also decreases.
Q.24. From the following elements:
4Be; 9F; 19K; 20Ca
(i) select the element having one electron in the outermost shell.
(ii) two elements of the same group.
Write the formula of and mention the nature of the compound formed by the union of 19K and element X(2, 8, 7). [CBSE 2015]
Ans. (i) 19K has one electron in the outermost shell. It has the electronic configuration :
2, 8, 8, 1.
(ii) 4Be and 2oCa belong to group 2.
Both of them have two electrons in the outermost shell and therefore belong to group 2 (same group).
Formula of the compound formed by the union of 19K and X(2, 8, 7) is KX.
Nature of the compound will be ionic because K(2, 8, 8,1) will donate one electron to X. This will complete the octet of both.
(a) What are ‘groups’ and ‘periods’ in the ‘periodic table’?
(b) Two elements M and N belong to group I and II respectively and are in the same period of the periodic table. How do the following properties of M and N vary?
Sizes of their atoms
Their metallic characters
Their valencies in forming oxides
Molecular formulae of their chlorides
Answer.
(a) The vertical columns in the periodic table are called ‘groups’. The horizontal rows in the periodic table are called ‘periods’.
(b)
‘M’ and ‘N’ belong to same
period but group I and II. Therefore, ‘N’ will be smaller than ‘M’ as atomic size goes on decreasing from left to right.‘M’ is more metallic than ‘N’. Metallic character goes on decreasing from left to right as tendency to lose electrons decreases due to decrease in atomic size.
Their valencies are 1 and 2 respectively in forming oxides.
Valency goes on increasing first
and then decreases.MCI, NCI2 are molecular formulae of their chlorides.
Did Mendeleev have gaps in his periodic table?
(b) any three limitations of Mendeleev’s classification.
(c) does electronic configurations of atoms change in a period with increase in atomic number?
Answer.(a)Gaps were left for undiscovered elements in the Mendeleev’s Periodic Table.
(b)(i) Position of hydrogen was not justified.
(ii)Increasing order of atomic mass could not be maintained.
(iii) Isotopes have similar chemical properties but different atomic masses, they cannot be given separate places.
(c)Number of shells remains the same, number of valence electrons goes on increasing
from left to right in a period till octet is complete,e.g.
Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different numbers of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral. Based on the above information answer the following questions:
To which group or period of the Periodic Table do the listed elements belong?
What would be the nature of compounds formed by a combination of elements B and F?
Which two of these elements could definitely be metals?
Which one of the eight elements is most likely to be found in gaseous state at room temperature?
If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G.
Answer.
A and B belong to group 1 and 2 because they form basic oxides. C belongs to group 13 as it has 3 valence electrons. D belongs to group 14 as it forms almost neutral oxide. E and F belong to group 15 and 16 as they form acidic oxides, G belongs to group 17 as it has 7 valence electrons and H belongs to group 18. They belong to the 3rd period of the Periodic Table because AG is NaCI, added in a small amount to almost all vegetable dishes during cooking and Na and Cl belong to the 3rd period.
Ionic compounds will be formed because ‘B’ is metal and ‘F’ is non-metal. ‘B’ can lose two electrons and ‘F’ can gain two electrons.
A and B are definitely metals as they form basic oxides.
G and H are gaseous at room temperature.
CG3 is the formula of the compound formed by combination of C and G.
Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different numbers of electrons in their outermost shells. It was found that elements A and G combine to form an ionic compound which can also be extracted from sea water. Oxides of the elements A and B are basic in nature while those of E and F are acidic. The oxide of element D is almost neutral. Answer the following questions based on the information given herein:
To which group or period of the periodic table do the listed elements belong?
Which one of the eight elements is likely to be a noble gas?
Which one of the eight elements would have the largest atomic radius?
Which two elements amongst these are likely to be non¬metals?
Which one of these eight elements is likely to be a semimetal or metalloid?
Answer.
A and B belong to group 1 and 2 because they form basic oxides. C belongs to group 13 as it has 3 valence electrons. D belongs to group 14 as it forms almost neutral oxide. E and F belong to group 15 – and 16 as they form acidic oxides, G belongs to group 17 as it has 7 valence electrons and H belongs to group 18. They belong to the 3rd period of the Periodic Table because sodium belongs to the 3rd period and AG is NaCI, ionic compound of sodium which can be obtained from sea water and A(Na) and G(CI) belong to the 3rd period.
He belongs to noble gas.
A has the largest atomic radius.
E and F are likely to be non-metals.
D is likely to be metalloid or semimetal.
How does the electronic configuration of an atom of an element relate to its position in the modern periodic table? Explain with one example.
Answer. The position of an element depends upon the number of valence electrons which depend upon electronic configuration. Those elements which have the same valence electrons occupy the same group.
Those elements which have one valence electron belong to group 1.
Elements with two valence electrons belong to group 2.
Period number is equal to number of shells.
If valence electrons are equal to 1, it belongs to group 1. If it has 2 shells, it belongs to the second period, e.g. if element ‘X’ has atomic number 11, its electronic configuration is 2, 8,1. It has one valence electron, it belongs to group 1 and it has three shells therefore, it is in the third period.
State the Modern Periodic Law for classification of elements. How many
(a) groups and (b) periods are there in the Modern Periodic Table?
Answer. ‘Properties of elements are the periodic
function of their atomic number.’
(a) There are 18 groups and
(b) 7 periods in the Modern Periodic Table.
Choose from the following:
6C, 8O, 10Ne, 11Na,14Si
(a) Elements that should be in the same period.
(b) Elements that should be in the same group.
State reason for your selection in each case.
Answer.
(a) 6C, 8O, 10Ne are in the same period, Le.
2nd period as they have two shells. nNa and 14Si are in the same period, i.e. 3rd period as they have three shells.
(b)6C,14Si are in the same group because they have the same number of valence electrons, i.e. four.
An element ‘X’ belongs to the 3rd period and group 17 of the periodic table. State its (a) electronic configuration, (b) valency. Justify your answer with reasoning.
Answer.
(a) X(17) : 2, 8, 7
(b) Valency : 1
It has atomic number 17 and therefore, electronic configuration will be 2, 8, 7. It can gain one electron to become stable therefore, its valency is equal to 1. It belongs to the third period, as it has three shells. It belongs to group 17 because it has 7 valence electrons.
Choose from the following:
20Ca,3Li,11Na,10Ne
(a) An element having two shells completely filled with electrons.
(b) Two elements belonging to the same group of the periodic table.
Answer.
(a) 10Ne has electronic configuration 2, 8. Its both shells are completely filled.
(b) 3lian nNa belong to same group of periodic table, ie. 1st group.
Why do all the elements of the (a) same group have similar properties, (b) same period have different properties?
Answer.
(a) Elements of the same group have similar properties due to the same number of valence electrons, therefore, they have the same valency.
(b) Elements of the same period have different properties as they differ in the number of valence electrons.
Periodic table class 10 NCERT CHEMISTRY long question:
.(a) How many periods are there in the Modern Periodic Table of elements?
(b) How do atomic radius, valency and metallic character vary down a group?
(c) How do the atomic size and
metallic character of elements vary as we move from left to right in a period?
Answer.
(a) There are 7 periods.
(b) Atomic radius goes on increasing down the group, valency remains same. Metallic character increases down the group.
(c) Atomic size decreases along a period from left to right. Metallic character decreases along a period from left to right.
How do the following change?
Number of shells of elements as we go down a group.
Number of valence electrons of elements moving from , left to right in a period.
Atomic radius in moving from left to right along a period.
Atomic size down a group.
Answer.
(a)
Different elements in same group
have the same number of valence electrons.Number of shells of elements in the same period are equal.
(b)
Number of shells of elements
goes on increasing down the group.Number of valence electrons of elements goes on increasing on moving from left to right in a period, e.g. lithium has 1, beryllium has 2, boron has 3, carbon has 4, nitrogen has 5, oxygen has 6, fluorine has 7 and neon has 8 valence electrons.
Atomic radius goes on decreasing in moving from left to right along a period.
Atomic size goes on increasing down a group.
Which two criteria did Mendeleev use to classify the elements in his Periodic Table?
(b) State Mendeleev’s periodic law.
(c) Why could no fixed position be given to hydrogen in Mendeleev’s Periodic Table?
(i) Sizes of their atoms
(ii) Their metallic characters
(iii) Their valencies in forming oxides
(iv) Molecular formulae of their chlorides
(a) The vertical columns in the periodic table are called ‘groups’. The horizontal rows in the periodic table are called ‘periods’.
(b) (i) ‘M’ and ‘N’ belong to same
period but group I and II. Therefore, ‘N’ will be smaller than ‘M’ as atomic size goes on decreasing from left to right.
(ii) ‘M’ is more metallic than ‘N’. Metallic character goes on decreasing from left to right as tendency to lose electrons decreases due to decrease in atomic size.
(iii) Their valencies are 1 and 2 respectively in forming oxides. Valency goes on increasing first
and then decreases.
(iv) MCI, NCI2 are molecular formulae of their chlorides.
(d) How and why does the atomic size vary as you go
(i) from left to right along a period?
(ii) down a group?
Answer.
(a) (i) Increasing order of atomic mass as physical property and similarities in chemical properties of elements.
(ii) The formulae and nature of hydrides and oxides formed by elements was treated as basic chemical properties for its classification.
(b) Properties of elements are the periodic functions of their atomic masses.
(c) It is because it resembles both alkali metals as well as halogens.
(d) (i) Atomic size goes on decreasing
from left to right because one proton and one electron is being added successively therefore, force of attraction between . valence electrons and nucleus increases hence, the atomic size decreases.
(ii) The atomic size goes on increasing from top to bottom in a group because the number of shells keeps on increasing therefore, the distance between nucleus and valence electrons increases.
Q.1. (a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all the three attempts.'
(b) Name the scientist who first of all showed that the atomic number of an element is a more fundamental property than its atomic mass.
(c) State Modern periodic law. [CBSE 2018]
Ans. (a) Dobereiner Attempt:
Advantage: The atomic mass of the middle element of the triad was the mean of the other two elements.
Limitation: Dobereiner could identify only three triads.
Newland Attempt:
Advantage: Every eighth element has properties similar to that of the first. Sodium is the eighth element after lithium. These two elements have similar properties.
Limitation: Newlands law of Octaves was found to be applicable only up to calcium. After calcium, every eight elements did not possess properties similar to that of the first.
Mendeleev Attempt:
Advantage: The elements were arranged on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties.
Limitation: No fixed position in the periodic table could be given to hydrogen by Mendeleev classification.
(b) Henry Moseley.
(c) Properties of elements are a periodic function of their atomic number.
Q.2. The atomic number of Cl is 17. On the basis of this information, answer the questions that follow : [CBSE 2017]
(a) Write the electronic configuration of Cl.
(b) Find the valency.
(c) To which group does it belong ?
(d) Identify the type of ion it will form.
(e) Write down the formula of the compound it forms with other elements.
Ans.
(a) Electronic configuration of Cl is 2, 8, 7.
(b) Valency of Cl is 1 as it requires only one electron to complete its octet.
(c) It belongs to group 17 of the modern periodic table.
(d) It will form an anion (Cl-) by gaining one electron.
(e) It forms HCl with H and NaCl with Na.
Q.3. In the following table, the positions of six elements A, B, C, D, E and F are given as they are in the Modern Periodic Table:
On the basis of the above table, answer the following questions:
(i) Name the element which forms only covalent compounds.
(ii) Name the element which is a metal with valency three.
(iii) Name the element which is a non-metal with valency three.
(iv) Out of D and E, whose atomic radius is bigger and why?
(v) Write the common name for the family to which the elements C and F belong. [Foreign 2015]
Ans.
(i) ‘E’ forms only covalent bonds.
(ii) ‘D’ is metal with valency three.
(iii) ‘B’ is non-metal with valency 3.
(iv) ‘D’ is bigger due to less effective nuclear charge.
(v) ‘C’ and 'F' belong to noble gasses.
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