Page 118 - ICSE Chemistry 8

B. Read the following paragraph. Iden fy the incorrect parts.
Valency refers to the exchanging capacity of an atom of a compound. The valency of an element is
always a whole number that varies from 0 to 6. The outermost shell of an atom is called the electron
shell and the electrons present in the electron shell are called valent electrons. Lithium and sodium are
divalent elements. Oxygen and magnesium are monovalent elements. Boron and aluminium are trivalent
elements. Silicon is a pentavalent element.

C. Answer in detail.
1. Write the rules that are applied for represen ng the elements.

2. How is the chemical formula of a compound derived? Explain with the help of an example.
3. State the ways in which we can balance a chemical equa on. Also give examples.
4. Write the informa on gathered from a chemical equa on.

5. Discuss the limita ons of a chemical equa on.

OBSERVE AND PERFORM

Observe the given table carefully and answer the following ques ons.

Element Valency Element Valency
Nitrogen 3, 5 Iron 2, 3

Phosphorus 3, 5 Cobalt 2, 3

Sulphur 2, 4, 6 Copper 1, 2
Chlorine 1, 3, 5, 7 Iodine 1, 3, 5, 7

Manganese 2, 3, 4, 6, 7 Lead 2, 4

1. Name the elements exhibi ng valency 3 and 5 both. Write their symbols.

2. Write the symbols of the elements exhibi ng valency 2 and 3 both.
3. Name the elements exhibi ng valency 2, 4 and 6. Write their symbol.

4. Name the elements exhibi ng valency 1, 3, 5 and 7. Write their symbol.
5. Write the symbol of the element exhibi ng valency 2, 3, 4, 6 and 7.

APPLY YOUR LEARNING LIFE SKILLS

A. What is the valency of the element represented In a group of two or three students, make
using the symbol Mg? a chart that depicts important and simple
B. What is the La n name of the element represented chemical equa ons showing the physical
using the symbol Cu? states of the reactants and products.
C. What is the chemical formula and valency of the (Team work and Coopera on)
radicals: phosphate and bisulphate?

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