CBSE Class 10 Science Periodic Classification Of Elements Assignment Set G

Very Short Answer Type Questions :

Question. Name any two pairs of elements which were adjusted by Newlands in the same slot.
Answer: (i) Co and Ni, (ii) Ce and La

Question. Define Newlands law of octaves.
Answer: Newlands Law of Octaves: When elements are arranged in increasing order of their atomic mass, every eighth element resembles with the first.

Question. State Mendeleev’s periodic law.
Answer: Mendeleev’s Periodic Law: Properties of elements are a periodic function of their atomic mass.

Question. Name any two elements which were discovered later after the formation of Mendeleev’s periodic table.
Answer: Gallium and Germanium.

Question. What is a metalloid? Name any two of them.
Answer: Metalloids are those elements which resembles both with metals as well as non-metals e.g., Boron and Silicon.

Question. Write the number of horizontal rows in the modern periodic table. What are these rows called?
Answer: There are 7 horizontal rows in the modern periodic Table. These rows are called periods.

Question. The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to same group as magnesium.
Answer: The valency of Mg is 2. The valency of Ba is also 2 as they belong to the same group. Formula of Barium nitrate is Ba(NO3)2, and that of Barium sulphate is BaSO4.

Question. Write one difference between Group 1 and Group 2 elements?
Answer: Group 1 elements has 1 valence electron whereas group 2 elements has 2 valence electrons.

Question. Chlorine, Bromine and Iodine form Dobereiner’s triads. The atomic mass of Cl and I are 35.5 and 126.9 respectively. Predict the atomic mass of Bromine.
Answer: Atomic Mass of Br
= Atomic mass of Cl + Atomic mass of I/2
= 35.5 + 126.9 = 162 4/2 = 81.2
Electronic configuration: X = 2,8,7
It has 7 valence electrons. It belongs to group 17.
It has 3 shells, therefore it belongs to 3rd period.
It can gain 1 electron to become stable, so its valency is equal to 1.

Question. Write the trend of atomic size and metallic character along a group and a period in modern periodic table.
Answer: Atomic size increases down the group and decreases along a period from left to right in the periodic table.
Metallic character increases down the group and it decreases along a period from left to right.

Question. The electronic configuration of two elements X and Y are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic numbers of X and Y.
Answer: X = 2 + 8 + 7 = 17
Y = 2 + 8 + 8 + 3 = 21

Question. Elements in Periodic table show periodicity in properties. List any four such properties.
Answer: Valence electrons, Valency, Atomic size, Metallic character.

Question. How does metallic character of the elements change along a period in the periodic table from left to right and why?
Answer: Metallic character of elements decreases along a period from left to right because atomic size decreases, tendency to lose electrons decreases.

Question. Which has larger atomic radius, K(19) or Ca(20)?
Answer: K has larger atomic radius than Ca.

Question. Write the formula which is used to determine the maximum number of electrons that a shell can accommodate.
Answer: 2n₂, where n is the shell number.

Question. Arrange the following elements in increasing order of their atomic radii:
a. Li, Be, F, N
b. Cl, At, Br, I
Answer: a. F < N < Be < Li
b. Cl < Br < I < At

Question. What is the valency of an element with atomic number 35?
Answer: Atomic number is 35, it has electronic configuration of 2, 8, 18, 7. It has 7 valence electrons, therefore its valency is equal to 1.

Short Answer Type Questions :

Question. The position of three elements A, B and C in the Periodic Table is shown below:

Giving reasons, explain the following:
(a) Element A is non-metal.
(b) Atom of element C has a larger size ‘ than atom of element A.
(c) Element B has a valency of 1.
Answer: (a) It is because it has 7 valence electrons.
It can gain one electron to form negative ion. So, it is a non-metal.
(b)’C’ has more number of shells than A. So, it is larger in size.
(c)’B’ has one valence electron. It can lose one electron to become stable. So, its valency is equal to 1.
Question. The position of three elements A, B and C in the Periodic Table is shown below:

Giving reasons, explain the following:
(a) Element A is a non-metal.
(b) Element B has a larger atomic size than element C.
(c) Element C has a valency of 1
Answer: (a) ‘A’ is non-metal because it can gain electron easily as it has 7 valence electrons and forms negative ion with stable electronic configuration.
(b) It is because ‘B’ has lesser atomic number, less nuclear charge, less force of attraction between valence electrons and nucleus therefore, has larger atomic size.
(c) ‘C’ has 7 valence electrons. It can gain one electron to become stable. So, its valency is equal to one.

Question. Table given below shows a part of the Periodic Table.

Using this table, explain why :
(a) Li and Na are considered as active metals.
(b) Atomic size of Mg is less than that of Na. (c) Fluorine is more reactive than Chlorine.
Answer: (a) They can lose electrons easily due to bigger size; energy required to remove electron is less.
(b) It is because of greater effective nuclear charge on Mg, i.e. more number of protons attract more number of electrons than Na.
(c) ‘F’ can form F– more easily than Cl due to smaller atomic size. F– is more stable than Cl–.
Therefore, fluorine is more reactive than chlorine.

Question. In the following table, are given eight elements A, B, C, D, E, F, G and H (here letters are not the usual symbols of the elements) of the Modern Periodic Table with the atomic numbers of the elements in parenthesis.

(a) What is the electronic configuration of F?
(b) What is the number of valence electrons in the atom of F?
(c) What is the number of shells in the atom of F?
(d) Write the size of the atoms of E, F, G and H in decreasing order,
(e) State whether F is a metal or a non-metal.
(f) Out of the three elements B, E and F, which one has the biggest atomic size?
Answer: (a) F has electronic configuration 2, 8, 2.
(b) F has 2 valence electrons.
(c) There are three shells in ‘F’.
(d) H > G > F > E is decreasing order of size of atoms.
(e) ‘F’ is a metal.
(f) ‘B’ is having biggest atomic size among B, E and F.

Question. In the following table, six elements A, B, C, D, E and F (here letters are not the usual symbols of the elements) of the Modern Periodic Table with atomic numbers 3 to 18 are given:

(a) Which of these halogen ?is (i) a noble gas, (ii) a halogen
(b) If B combines with F, what would be the formula of the compound formed?
(c) Write the electronic configurations of C and E.
Answer: (a) (i) G is a noble gas
(i) F is a halogen
(b) BF will be the formula of the compound formed

(c) C has atomic number 12 and electronic configuration is K = 2, L = 8, M = 2
E has atomic number 8 and electronic configuration is K = 2, L = 6

Question. Out of the elements H(1), Be(4), Na(11) and Mg(12).
a. Write the pair of elements having similar chemical properties.
b. State the group number of each pair,
c. Name one another element belonging to each of these groups.
Answer: a. Be(4) and Mg(12) have similar chemical properties.
H( 1) and Na(ll) have similar chemical properties.
b. Be and Mg belong to group 2, H and Na belong to group 1.
c. K belongs to group 1 and Ca belongs to group 2.

Question. 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 decreases from Li to F.
b. Identify the most (i) metallic and (ii) non-metallic element.
Answer: a. It is because effective nuclear increases due to increase in forces of attraction between more electrons with more protons, even though number of shells remain the same.
b. (i) Li is the most metallic element, (ii) F is the most non-metallic element.

Question. Na, Mg and Al are the elements having one, two and three valence electrons respectively. Which of these elements (a) has the largest atomic radius, (b) is least reactive? Justify your answer stating reason for each.
Answer: (a) Na has the largest atomic radius because it has 11 protons and 11 electrons, therefore least effective nuclear charge.
(b) Al is least reactive because it has smallest atomic size due to 13 protons and 13 electrons, it has greater effective nuclear charge, therefore, cannot lose electrons easily, hence it is least reactive.

Question. The atomic numbers of three elements are given below:

Write the symbol of the element which belongs to (a) group 1, (b) group 14, of the periodic table. State the period of the periodic table to which these elements belong. State reason to support your answer.
Answer: (a) A belongs to group 1.
(b) B belongs to group 14.
These elements belong to second period because these elements have two shells. A has electronic configuration 2, 1 and has one valence electron so, belongs to group 1. ‘B’ has electronic configuration 2, 4 and has four valence electrons so, belongs to group 14 and period 2. ‘C’ has electronic configuration 2, 7 and has one valence electron. All of them contain two shells and so belong to second period.

Question. The atomic number of an element is 19.
a. Write the electronic configuration of this element and determine (i) the valency of this element, and (ii) whether this element is a metal or a nonmetal?
b. Write the formula of the oxide of this element.
c. Is this element more reactive or less reactive than Na (atomic number 11)? Justify your answer, giving example.
Answer: a. 2, 8, 8, 1
i. Valency = 1
ii. It is a metal.
a. X₂O
b. It is more reactive than Na(11) because it is large in size and it can lose electrons easily due to less effective nuclear charge.
K reacts more vigorously with H₂O than Na.

Question. Why is atomic number considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table? How does the metallic character of elements vary as we move (a) from left to right in a period, and (b) top to bottom in a group of the modem periodic table? 
Answer: It is because chemical properties depend upon the number of valence electrons which is determined with the help of atomic number.
a. Metallic character decreases from left to right because atomic size decreases, tendency to lose electrons decreases,
b. Metallic character increases from top to bottom in a group because atomic size increases due to which effective nuclear charge decreases.

Question. An element X’(Atomic number 20) burns in the 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.
Answer: a. X is calcium because it forms CaO (basic oxide). Its electronic configuration is 2, 8 8, 2.
b. It belongs to group 2 and 4th period.
c. CaO + H₂O → Ca(OH)₂

Question. How does valency of the elements vary
a. in going down a group, and
b. in going from left to right in a period of the periodic table?
Answer: a. It remains the same.
b. It first increases till middle, then decreases.

Question. Calcium is an element with atomic number 20.
a. Will it be a metal/non-metal?
b. What will be its valency?
c. What would be the formula of its chloride?
d. Will it be smaller / larger than K?
Answer: Ca(20): 2, 8, 8, 2
a. It will be a metal.
b. Its valency is equal to 2.
c. CaCl₂ is the formula of its chloride.
d. It will be smaller than K.

Question. The position of three elements A, B and C in the periodic table are indicated below:
Answer: Group 16 Group 17
– – (First Period)
– A (Second Period)
– – (Third Period)
B C Fourth Period)
a. State whether element C would be a metal or a non-metal. Why?
b. Which is the more active element, A or C? Why?
c. Which type of ion (cation or anion) will be formed by the element C? Why?
Ans : a. O is a non-metal because it has 7 valence electrons.
It can gain one electron to form an anion.
b. A is more reactive than C because it is smaller in size, therefore it can gain electron(s) easily.

Question. The electrons in the atoms of four elements A, B, C and D are distributed in three shells havingl, 3, 5 and 7 electrons in the outermost shell respectively. State the period in which these elements can be placed in the modern periodic table. Write the electronic configuration of the atoms of A and D and the molecular formula of the compound formed when A and D combine.
Answer: A: 2, 8, 1
B: 2, 8, 3
C: 2, 8, 5
D: 2, 8, 7
They belong to the 3rd period.

AD is the molecular formula.

Question. a. How many periods are there in the Modem Periodic Table of elements?
b. How do atomic radius, valency and metallic character vary down a group?
c. How do 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 and Metallic character increases down the group. Valency remains the same in a group.
c. Atomic size and metallic character decrease along a period from left to right in a period.

Question. Explain the variation in the following properties of the elements in periodic table:
a. Atomic radius in the periodic table,
b. Metallic character in a period,
c. Valency in a group.
Answer: a. Atomic radius and Metallic character increases down the group. Valency remains the same in a group.
b. Atomic size and metallic character decrease along a period from left to right in a period.

Question. The elements of group 18 of the periodic table are given:
He, Ne, Ar, Kr, Xe, Rd, Dg
a. The elements of this group are unreactive, why?
b. Which atom is bigger in size Ne or Ar and why?
Answer: a. It is because they have their octet complete i.e., stable electronic configuration.
b. Ar has bigger atomic size than Ne because Ar has 3 shells while Ne has 2 shells; Ar (2, 8, 8), Ne (2, 8)

Question. a. How does electropositivity of elements gets affected as we move (i) down the group, (ii) across the period?
b. Which atomic property increases both ways: as we move across the period or down the group?
Answer: a. (i) Electropositivity increases down the group.
(ii) Electropositivity decreases across the period from left to right.
b. Atomic number increases across the period as well as down the group.

Question. (a) Identify the element that have two completely filled shells and the number of valence electrons in each case if atomic numbers are: (i) 1, (ii) 2,
(iii) 7, (iv) 8
(b) Analyse which amongst them is inert.
Answer: a. (i) 2, 8, 1: Sodium
(ii) 2, 8, 2: Magnesium
(iii) 2, 8, 7: Chlorine
(iv) 2, 8, 8: Argon
(b) Argon is inert.

Question. Atoms of seven elements A, B, C, D, E, F and G have a different number of electronic shells but have the same number of electrons in their outermost shells.
The elements A and C combines with chlorine to form an acid and common salt respectively. The oxide of element A is liquid at room temperature and it is a neutral substance, while the oxides of the remaining six elements are basic in nature. Based on the above information, answer the following question:
a. What could the element A be?
b. Will elements A to G belong to the same period or same group of the periodic table?
c. Write the formula of the compound formed by the reaction of the element A with oxygen.
d. Show the formation of the compound by the combination of element C with chlorine with the help of electronic structure.
e. What would be the ratio of number of combining atoms in a compound formed by the combination of element A with carbon?
f. Which one of the given elements is likely to have the smallest atomic radius?
Answer: a. A is hydrogen.
b. A and G will belong to the same group.
c. H₂O is the formula of the compound.
d. C is sodium.
Na → Na+ + e- or C → C+ + e-
Cl + e- → Cl- or Cl + e-→Cl

e. CA4 i.e., 1:4
f. A has smallest atomic radius.

Question. Based on the group valency of elements state the formula for the following giving justification for each:
a. Oxides of 1st group elements,
b. Halides of the elements of group 13, and c. Compounds formed when an element of group 2 combines with an element of group 16.
Answer: a. M₂O
b. MCl₃
c. CaO

Question. Table given below shows a part of the modern periodic table.

Using this table, explain why
a. Li and Na are considered as active metals.
b. Atomic size of Mg is less than that of Na.
c. Fluorine is more reactive than chlorine.
Answer: a. Li and Na have largest atomic size in respective period, therefore they can lose an electron easily, hence they are active metals.
b. Mg has 12 protons and 12 electrons which has more forces of attraction, therefore, it is smaller in size than Na which is having 11 protons and 11 electrons.
c. F is smaller in size, it can gain electrons easily, therefore, it is more reactive than Cl.

Question. The element Be, Mg and Ca are placed in the second group of the periodic table. Their atomic numbers are
4, 12, 20 respectively
a. Write the electronic configuration of these elements.
b. Write the valency exhibited by them,
c. Which three elements will be the most reactive?
Answer: a.

b. Valency is 2.
c. Ca is the most reactive metal.

Question. In the figure given below the first 20 elements are jumbled up. Carefully observe the figure and answer the following questions:

a. Pick out the two elements which are known as alkali metals.
b. Pick out the two elements which have valency of 4.
c. Pick out two elements which belong to group 16 of the periodic table.
Answer: a. Na, K are alkali metals.
b. C, Si have valency equal to 4
c. O and S belongs to group 16.

Question. What is meant by ‘group’ in the modern periodic table? How do the following change on moving from top to bottom in a group?
a. Number of valence electrons.
b. Number of occupied shells.
c. Size of atoms.
d. Metallic character of elements.
e. Effective nuclear charge experienced by valence electrons.
Answer: The vertical column of the periodic table is called group.
a. Number of valence electrons remains the same in a group.
b. Number of occupied shells goes on increasing down a group.
c. Size of atom increases down the group.
d. Metallic character of element increases down the group.
e. Effective nuclear charge decreases down the group.

Question. Lithium, Sodium, Potassium are placed in the same group on the basis of their similar properties. List three such similar properties.
Answer: a. All of them are reactive metals.
b. They have 1 valence electron and form positive ions with +1 charge.
c. They are largest in size in their respective periods.