TN 10th Science Guide

8. Periodic Classification of Elements

I. Choose the best answer.

1. The number of periods and groups in the periodic table are ____.

(a) 6, 16 (b) 7, 17
(c) 8, 18 (d) 7, 18.

2. The basis of modern periodic law is:

(a) atomic number
(b) atomic mass
(c) isotopic mass
(d) number of neutrons

3. _____ group contains the member of the halogen family.

(a) 17^th (b) 15^th
(c) 18^th (d) 16^th .

4. _______is a relative periodic property.

(a) atomic radii
(b) ionic radii
(c) electron affinity
(d) electronegativity

5. Chemical formula of rust is ____.

(a) FeO.xH₂O
(b) FeO₄.xH₂O
(c) Fe2O3.xH2O
(d) FeO.

6. In the aluminothermic process the role of Al is ____.

(a) oxidizing agent
(b) reducing agent
(c) hydrogenating agent
(d) sulphurising agent.

7. The process of coating the surface of metal with a thin layer of zinc is called:

(a) painting (b) thinning
(c) galvanization (d) electroplating

8. Which of the following have inert gases 2 electrons in the outermost shell?

(a) He (b) Ne
(c) Ar (d) Kr.

9. Neon shows zero electron affinity due to:

(a) stable arrangement of neutrons
(b) stable configuration of electrons
(c) reduced size
(d) increased density

10. ______ is an important metal to form an amalgam.

(a) Ag (b) Hg
(c) Mg (d) Al.

II. Fill in the blanks.

1. If the electronegativity difference between two bonded atoms in a molecule is greater than 1.7, the nature of bonding is Ionic bond.

2. Sixth period is the longest period in the periodical table.

3. Atomic number forms the basis of modem periodic table.

4. If the distance between two Cl atoms in Cl₂ molecule is 1.98 Å, then the radius of the Cl atom is 0.99 Å.

5. Among the given species A^–, A⁺, and A, the smallest one in size is A+

6. The scientist who propounded the modem periodic law is Henry Moseley.

7. Across the period, ionic radii Decreases

8. Lanthanides and Actinides are called inner transition elements.

9. The chief ore of Aluminium is Bauxite (Al₂O₃.2H₂O).

10. The chemical name of rust is Hydrated ferric oxide.

III. Match the following.

1. Galvanisation	(b) Coating with Zn
2. Calcination	(e) Heating in the absence of air
3. Redox reaction	(d) Alumino thermic process
4. Dental filling	(c) Silver-tin amalgam
5. Group 18 elements	(a) Noble gas elements

IV. True or False: (If false give the correct statement)

1. Moseley’s periodic table is based on atomic mass.
Answer: False.
Correct Statement: Moseley’s periodic table is based on atomic number.

2. Ionic radius increases across the period from left to right.
Answer: False.
Correct Statement: Ionic radius decreases across the period from left to right.

3. All ores are minerals, but all minerals cannot be called as ores.
Answer: True.

4. Al wires are used as electric cables due to their silvery – white colour.
Answer: False.
Correct Statement: Al wires are used as electric cables due to their good conductor of electricity.

5. An alloy is a heterogeneous mixture of metals.
Answer: False.
Correct Statement: An alloy is a homogenous mixture of metals.

V. Assertion and Reason:

Answer the following questions using the data given below.
(i) A and R are correct, R explains the A.
(ii) A is correct, R is wrong.
(iii) A is wrong, R is correct.
(iv) A and R are correct, R doesn’t explain A.

1. Assertion: The nature of bond in HF molecule is ionic
Reason: The electronegativity difference between H and F is 1.9.
Answer: (i) A and R are correct, R explains the A.

2. Assertion: Magnesium is used to protect steel from rusting.
Reason: Magnesium is more reactive than iron.
Answer:
(i) A and R are correct, R explains the A.

3. Assertion: An uncleaned copper vessel is covered with a greenish layer.
Reason: copper is not attacked by alkali
Answer:
(iv) A and R are correct, R doesn’t explain A.

VI. Short Answer Questions.

1. A is a reddish-brown metal, which combines with O₂ at < 1370 K gives B, a black coloured compound. At a temperature > 1370 K, A gives C which is red in colour. Find A, B and C with reaction.

(i) Reddish brown metal (A) is copper.

compound molecular formula name	compound molecular formula name	compound molecular formula name
A Cu copper	A Cu copper	A Cu copper
B CuO copper (ii) oxide	B CuO copper (ii) oxide	B CuO copper (ii) oxide
C Cu2O copper (i) oxide	C Cu2O copper (i) oxide	C Cu2O copper (i) oxide

On heating at different temperatures in the presence of oxygen,

copper forms two types of oxides CuO,Cu2O.

2. A is a silvery – white metal. A combines with O₂ to form B at 800°C, the alloy of A is used in making the aircraft. Find A and B.
Answer:
(i) Silver – white metal (A) is Aluminium.

(ii) (A) combines with O₂ to form aluminium oxide at 800°C.

(iii) Duralumin is the alloy of Al, which is used to make aircraft

A	Aluminium	Al
B	Aluminium oxide	Al₂O₃

3. What is rust? Give the equation for formation of rust.
Answer:
Rust is hydrated ferric oxide, Fe₂O₃.xH₂O. It is formed when iron is exposed to moist air.
4 Fe + 3O₂ + xH₂O ⟶ 2Fe₂O₃.xH₂O

4. State two conditions necessary for rusting of iron.

Conditions for rusting of iron:

The presence of water and oxygen is essential for the rusting of iron.
Impurities in the iron, the presence of water vapour, acids, salts and carbon dioxide hasten to rust.
Pure iron does not rust in dry and CO₂ free air. It also does not rust in pure water, free from dissolved salts.

VII. Long Answer Questions

1. (a) State the reason for the addition of caustic alkali to bauxite ore during purification of bauxite.
(b) Along with cryolite and alumina, another substance is added to the electrolyte mixture. Name the substance and give one reason for the addition.
Answer:
(a) Naturally, Bauxite is not soluble in normal solvents. Therefore the addition of caustic alkali to bauxite plays an important role while extraction of aluminium. Caustic alkali dissolves bauxite forming soluble sodium meta aluminate while impurities remain insoluble and precipitate as red mud.

(b) Along with cryolite and alumina, another substance is added to the electrolyte mixture is Fluorspar. Adding of fluorspar lowers the fusion temperature of the electrolyte.

2. The electronic configuration of metal A is 2, 8, 18, 1. The metal A when exposed to air and moisture forms B a green layered compound. A with conc. H₂SO₄ forms C and D along with water. D is a gaseous compound. Find A, B, C and D.
Answer:
(i) The electronic configuration of metal (A) is 2, 8, 18, 1. A is copper (Z = 29)

(ii) (A) Copper exposed to air and moisture forms green layered compound (B) that is a copper carbonate.

(iii) Copper (A) reacts with conc.H₂SO₄ to give copper sulphate (C) and Sulphur dioxide (D).
Cu + 2H2SO4 ⟶ CuSO4 + SO2↑ + 2H2O

compound molecular formula name	compound molecular formula name	compound molecular formula name
A Cu copper	A Cu copper	A Cu copper
B CuCO3. Cu(OH)2 malachite green	B CuCO3. Cu(OH)2 malachite green	B CuCO3. Cu(OH)2 malachite green
C CuSO4 copper sulphate	C CuSO4 copper sulphate	C CuSO4 copper sulphate
D SO2 sulphurdioxide	D SO2 sulphurdioxide	D SO2 sulphurdioxide

3. Explain the smelting process.
Answer:
Smelting (in a Blast Furnace): The charge consisting of roasted ore, coke and limestone in the ratio 8 : 4 : 1 is smelted in a blast furnace by introducing it through the cup and cone arrangement at the top. There are three important regions in the furnace.

(a) The Lower Region (Combustion Zone): The temperature is at 1500°C. In this region, coke bums with oxygen to form CO₂ when the charge comes in contact with a hot blast of air.

It is an exothermic reaction since heat is liberated.

(b) The Middle Region (Fusion Zone): The temperature prevails at 1000°C. In this region, CO₂ is reduced to CO.

Limestone decomposes to calcium oxide and CO₂

These two reactions are endothermic due to absorption of heat. Calcium oxide combines with silica to form calcium silicate slag.
CaO + SiO₂ → CaSiO₃

(c) The Upper Region (Reduction Zone): The temperature prevails at 400°C . In this region carbon monoxide reduces ferric oxide to form a fairly pure spongy iron.

The molten iron is collected at the bottom of the furnace after removing the slag.
The iron thus formed is called pig iron. It is remelted and cast into different moulds. This iron is called cast iron.

VIII. HOT Questions.

1. Metal A belongs to period 3 and group 13. A in red hot condition reacts with steam to form B. A with strong alkali forms C. Find A, B and C with reactions.
Answer:
(i) Metal (A) belongs to period 3 and group 13, is Aluminium (Al).

(ii) (A) Al in red hot condition reacts with steam to form Aluminium oxide (B).

(iii) Aluminium (A) reacts with strong alkali forms of sodium meta aluminate (C).

compound molecular formula name	compound molecular formula name	compound molecular formula name
A Al aluminium	A Al aluminium	A Al aluminium
B Al2O3 aluminium oxide	B Al2O3 aluminium oxide	B Al2O3 aluminium oxide
C NaAlO2 sodium meta aluminate	C NaAlO2 sodium meta aluminate	C NaAlO2 sodium meta aluminate

2. Name the acid that renders aluminium passive. Why?
Answer:
Dil. or cone. HNO₃ does not attack aluminium, but renders Al passive due to the formation of oxide film on its surface.

3. (a) Identify the bond between H and F in the HF molecule.
(b) What property forms the basis of identification?
(c) How does the property7 vary in periods and in groups?
Answer:
(a) The nature of the bond in the HF molecule is ionic.
(b) Electronegativity.
(c) Along the period, from left to right in the periodic table the electronegativity increases because of the increase in the nuclear charge which in turn attracts the electrons more strongly. On moving down a group, the electronegativity of the elements decreases because of the increased number of energy levels.