CBSE Class 10 Chemistry Periodic Classification of Elements Worksheet Set H

Multiple Choice Questions 

Choose the correct answer from the given options.

Question. Which of the following statement(s) about the Modern Periodic Table are incorrect?
(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number
(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses
(iii) Isotopes are placed in adjoining group(s) in the Periodic Table
(iv) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number
(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only
Answer : B

Question. An element ‘X’ with atomic number 11 forms a compound with element ‘Y’ with atomic number 8. The formula of the compound formed is
(a) XY
(b) X₂Y
(c) XY₂
(d) X₂Y₃
Answer : B

Question. 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
Answer : C

Question. Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 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. Element ‘X’ forms a chloride with formula XCl₂, which is a solid with high melting point. ‘X’ would most likely to be in the same group of the periodic table as:
(a) Na,
(b) Mg,
(c) Al
(d) Si
Answer : B

Question. Consider the following statements about an element ‘X’ with number of protons 13.
(A) It forms amphoteric oxide (B) Its valency is three
(C) The formula of its chloride is XCl3
The correct statements(s) is/are
(a) only (A)
(b) only (B)
(c) (A) and (C)
(d) (A), (B) and (C)
Answer : D

Question. On the basis of electronic configuration of ₅⁹ X, the group number and period of the element ‘X’ is:
(a) Group 15 period 2
(b) Group 13 period 2
(c) Group 19 period 5
(d) Group 13 period 5
Answer : B

Question. An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be
(a) Group 1 and Period 3
(b) Group 2 and Period 3
(c) Group 13 and Period 3
(d) Group 16 and Period 3
Answer : D

Question. 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
Answer : C

Very Short Answer Type Questions

Question. State modern periodic law.
Answer : Properties of elements are a periodic function of their atomic number

Question. Out of the three elements P, Q and R, having atomic number 11, 17 and 19 respectively, which two elements will show similar properties and why?
Answer : P(11): 2, 8, 1, Q(17): 2, 8, 7, R(19): 2, 8, 8, 1
‘P’ and ‘R’, because they have the same number of valence electrons.

Question. An element ‘A’ has atomic number 17. To which group and period does it belong?
Answer : Its electronic configuration is 2, 8, 7. It belongs to group 17 and 3rd period

Question. Name the element having electronic configuration 2, 8, 3. What is its valency?
Answer : Aluminium, its valency is equal to 3, because it lose 3 electrons to become stable.

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 : 17 and 21 respectively.

Question. A metal ‘M’ belongs to 13th group in the modern periodic table. Write the valency of the metal.
Answer : 3

Question. P(3), Q(12), R(13), S(20), which two elements have similar chemical properties and why?
Answer : P(3): 2, 1; Q(12): 2, 8, 2; R(13): 2, 8, 3; S(20): 2, 8, 8, 2
‘Q’ and ‘S’ because they have the same number of valence electrons

Question. Give the number of elements in 2nd and 5th period of modern periodic table.
Answer : 2nd period has 8 elements, 5th period has 18 elements.

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

Question. What is the number of valence electrons in the last element of the 3rd period?
Answer : 8

Short Answer type Questions

Question. Lithium, sodium and potassium form a Dobereiner’s triad. The atomic masses of Li and K are 7 and 39, respectively. Predict the atomic mass of sodium.
Answer : Atomic mass of sodium = 7 + 39/2 + = 23

Question. Write two reasons responsible for late discovery of noble gases.
Answer : (i) They are less abundant in nature. (ii) They are least reactive

Question. Did Dobereiner’s triads also exist in the columns of Newlands’ octaves?
Answer : Yes, e.g. Li, Na, K is a part of Newlands’ law of octaves

Question. Why do you think the noble gases are placed in a separate group in the periodic table?
Answer : It is because these are least reactive and resemble each other

Question. Besides Gallium, which other elements have since been discovered to fill the gaps left by Mendeleev in his periodic table?
Answer : Scandium and Germanium

Question. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev.
Answer : GeCl₄, GaCl₃.

Question. What were the criteria used by Mendeleev in creating the periodic table?
Answer : (i) Increasing order of atomic mass (ii) Formula of oxides and hydrides

Question. Why was the system of classification of elements into triads not found suitable?
Answer : It is because all the elements discovered at that time could not be classified into triads.

Question. What was the basis of classification of elements by Newlands?
                       Or
Define Newlands’ law of octaves.
Answer : Elements were arranged in increasing order of atomic mass and every 8th element resembled with the first element.

Question. What were the limitations of Dobereiner’s classification?
Answer : (i) All the elements could not be classified into triads.
(ii) Only three triads could be identified resembling each other.

Question. Two elements A and B belong to group 1 and 2 respectively in the same period. Compare them with respect to:
(a) Valency (b) Size of atom (c) Formula of oxide
(d) Nature of oxide (e) Metallic character
Answer : Group 1 2
Elements A B
                        ⚪     ◯
(a) Valency A → 1, B → 2
(b) Size of atom → A is bigger atom than B.
(c) Formula of oxide → A₂O, BO
(d) Nature → Basic
(e) Metallic character → A is more metallic than B.

Question. You are given five elements with some description of each element, place them in the Modern Periodic Table.
(a) Essential for breathing and burning.
(b) Inactive, two electrons in the outermost shell.
(c) Atom has same number of protons, electrons and neutrons, used in fertilizer industry.
(d) Number of neutrons, protons are same used in building our bones.
(e) This element form the hardest naturally occurring substance as allotrope.
Answer : 

Question. Give all characteristics of group.
Answer : Characteristics of a group:
(a) Valence electrons → All elements show same valence electrons in a group.
(b) Valency → Valency of all the elements remains the same in a group.
(c) Atomic size → The atomic size goes on increasing down the group.
(d) Metallic character → In case of metals the metallic character increases down the group.
(e) Non-metallic character → In case of non-metals the non-metallic character decreases down the group.

Question. (a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place two isotopes of chlorine Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answers.
Answer : (a) Classification is done to study the properties of elements conveniently.
(b) Increasing order of atomic mass and similarity in chemical properties i.e. the nature of oxide and hydride formed.
(c) The gaps were left for undiscovered elements then.
(d) Noble gases were not invented at that time.
(e) Cl-35 and Cl-37 will be kept in the same slot as their chemical properties are same.

Question. Give the characteristics of a period.
Answer : In a period as we go from left to right:
(a) Valence electrons → Goes on increasing
1, 2, 3, 4, 5, 6, 7, 8.
(b) Valency → Valency first increases and then decreases
1, 2, 3, 4, 3, 2, 1, 0.
(c) Size of atom → Size of atom goes on decreasing
                  ⚪  ◯  〇  ○  ∘
(d) Metallic character → Decreases
(e) Non-metallic character → Increases

Question. The atomic number of element X is 17 predict its
(a) Physical state.
(b) Name of element.
(c) Formulae of its compound with hydrogen.
(d) Metal or Non-metal.
(e) Formulae of its molecule.
Answer : Atomic number of X = 17.
Electronic configuration = 2, 8, 7
(a) Physical state → Gas
(b) Chlorine
(c) HCl
(d) Non-metal
(e) Cl₂

Question. Name the following elements
(a) Two shells, both of which are completely filled.
(b) Three shells with 2 valence electrons.
(c) Group 1, two shells.
(d) Group 17, period 3.
(e) Metal, with valency 3 group number 13 period 3.
Answer : (a) Two shells → K L
Filled                    →           2, 8
Atomic number → 10
∴ Element — Neon.
(b) Three shells →     K, L, M
2 Valence electron → 2, 8, 2
Atomic number →12 ∴ Element = Magnesium
(c) Group 1
2 shells →                           K  L
Electronic configuration → 2, 1
Atomic number → 3 ∴ Element = Lithium
(d) Group 17
Period → 3,                        K L M
Electronic configuration → 2, 8, 7
Atomic number → 17, ∴ Element = Chlorine
(e) Group → 13
Valency → 3
Period → 3                          K L M
Electronic configuration → 2, 8, 3
∴ Atomic number → 13, ∴ Element = Aluminium.

Question. On the baiss of the table of Mendeleev’s Periodic Table
(a) Name the element which is in
(i) I group and 3rd period. (ii) VII group and 2nd period.
(b) Suggest the formula for the following:
(i) Oxide of nitrogen (ii) Hydride of oxygen
(c) In group VIII of Periodic Table, why does cobalt with atomic mass 58.93 appear before nickel having atomic mass 58.71?
(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his Periodic Table?
(e) Using atomic masses of Li, Na and K, find the average atomic mass of Li, and K and compare it with the atomic mass of Na. State the conclusion drawn from this activity.
Answer : (a) (i) Sodium (ii) Fluorine
(b) (i) N₂O₅ (ii) H₂O
(c) Co resembles with Rh and Ir whereas ‘Ni’ resembles with Pd and Pt.
(d) Germanium and scandium
(e) Li Na K                           Average atomic mass of Na
6.939 22.99 39.102         =  6.939 + 39.102 / 2 = 23.0205
The atomic mass of Na is the average atomic mass of Li and K and these elements resemble with each other.

Question. (a) Which 2 criteria did Mendeleev use to classify the elements in his table.
(b) State Mendeleev’s Periodic law.
(c) Why could no fixed position be given to hydrogen in Mendeleev’s Periodic Table.
(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 and similarities in chemical properties of elements.
(ii) The formula of oxides and hydrides formed by elements.
(b) Mendeleev’s Periodic Law → Properties of elements are periodic functions of their atomic masses.
(c) Hydrogen had no fixed position in Mendeleev’s Periodic table because it resembles alkali metal by forming positive ions and resembles halogens by forming diatomic molecule.
(d) (i) Atomic size decreases from left to right, as the valence electrons are attracted by the nucleus due to increase in the nuclear force.
(ii) The atomic size increases from top to bottom in a group because the number of shells keep on increasing therefore distance between nucleus and valencem electrons increases.

Question. (a) Why did Mendeleev left gaps in his Periodic Table?
(b) State any 3 limitations of Mendeleev’s classification.
(c) How does electronic configuration of atoms change in period with increase in atomic number?
Answer : (a) Mendeleev left some gaps for undiscovered elements, because he predicted that there would be such elements which will fit in the gaps in future. He also predicted the properties of these elements.
(b) 3 limitations are:
(i) Position of hydrogen was not justified.
(ii) Increasing order of atomic mass could not be maintained.
(iii) Isotopes were not given separate place as they have different atomic mass.
(c) In a period the valence electrons goes on increasing from left to right as the number of shells is same.

Question. (a) What are ‘groups’ and ‘periods’ in the Periodic Table?
(b) Two elements M and N belong to groups I and II respectively and are in the same period of the Periodic Table. How do the following properties of M and N vary?
(i) Sizes of their atoms.
(ii) Their metallic characters.
(iii) Their valencies in forming oxides.
(iv) Molecular formulae of their chlorides.
Answer : (a) The vertical column in the Periodic Table are called ‘groups’, the horizontal rows in the table are called periods.
(b) (i) ‘M’ and ‘N’ belong to the same period but group I and II respectively. N is smaller than M as the atomic size decreases on moving from left to right across the Periodic Table.
(ii) M is more metallic than ‘N’ because metallic character decreases from left to right as tendency to lose electrons decreases due to decrease in atomic size.
(iii) The valencies of M and N are 1 and 2 respectively, valency across the period first increases then decreases.
(iv) MCl and NCl₂.

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