Page 79 - Chemistry_Form_2

Chemistry
for Secondary Schools

4. Covalent bonding takes place between two or more non-metals. It involves
atoms of the non-metals sharing electrons that are in their outermost shells.
5. The ability of an atom to combine with other atoms according to the number
of electrons it can give, take or share is known as valency.
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6. The oxidation state (oxidation number) of an element is the number of
electrons that need to be added, shared or removed by its atom, to make a
neutral molecule. The oxidation number is arbitrary and may be positive,
negative or zero.

7. A radical is a group of atoms which behaves as a single unit and has an
overall positive or negative charge. A radical can also be an atom, molecule
or ion that has unpaired valence electron. Such a group maintains its identity
throughout any chemical reaction.

8. A chemical formula is a representation that uses chemical symbols to show
the proportions of the elements present in a chemical compound.
9. An empirical formula is the simplest way of writing a chemical formula
and indicates the ratio of the atoms in a compound.

10. A molecular formula is a chemical formula that shows the total number of
atoms of each element in a molecule of a substance.

11. A systematic way of naming items or substances of a particular category is
known as nomenclature.

Revision exercise 3

Choose the correct answer for Questions 1-11. For other questions, provide the
answers as per the demands indicated.

1. What is the valency of Group I elements?
(a) 1 (b) 2 (c) 3 (d) 4

2. What name is given to the force of attraction that holds atoms together to
form a molecule?
(a) Chemical change

(b) Chemical bond
(c) Friction
(d) Centripetal force

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