5.1 The Names And Formulae Of Compounds

Question 1

When the compound contains a metal and a non metal:

Answer 1

The name of the metal is given first. The name of the non metal is given after but ending with -ide.

Question 2

When the compound is made of two non metals:

Answer 2

If one is hydrogen, that is named first. Otherwise the one with the lower group number comes first. Then the name of the other non-metal, ending with -ide.

Question 3

What does the formula of giant structures tell you?

Answer 3

In giant structures like sodium chloride and silicone dioxide, the formula tells you the ratio of the ions or atoms in the compound.

Question 4

What does the formula of a molecular compound tell you?

Answer 4

In a molecular compound, the formula tells you exactly how many atoms are bonded together in each molecule.

Question 5

What is the valency of an element?

Answer 5

The valency of an element is the number of electrons its atoms lose, gain or share, to form a compound.

Question 6

Group I

Answer 6

In forming a compound, the atoms lose 1 electron. So the valency of the element is 1.

Question 7

Valency of Group II

Answer 7

In forming a compound, the atoms lose 2 electrons. So the valency of the element is 2.

Question 8

Group III

Answer 8

In forming a compound, the atoms lose 3 electrons. So the valency of the element is 3.

Question 9

Group IV

Answer 9

In forming a compound, the atoms share 4 electrons. So the valency of the element is 4.

Question 10

Group V

Answer 10

In forming a compound, the atoms gain or share 3 electrons. So the valency of the element is 3.

Question 11

Group VI

Answer 11

In forming a compound, the atoms gain or share 2 electrons. So the valency of the element is 2.

Question 12

Group VII

Answer 12

In forming a compound, the atoms gain or share 1 electron. So the valency of the element is 1.

Question 13

Group 0

Answer 13

Do not form compounds

Question 14

Hydrogen

Answer 14

In forming a compound, the atoms lose or share 1 electon. So the valency of the element is 1.

Question 15

Transition elements

Answer 15

In forming a compound, the atoms can lose different numbers of electrons. So the valency of the elements is variable.

Question 16

Writing formulae using valencies

Answer 16

1. Write down the valencies of the two elements.
2. Write down their symbols, in the same order as the elements in the name.
3. Add numbers after the symbols if you need to, to balance the valencies.

Question 17

Writing formulae by balancing charges.

Answer 17

In an ionic compound, the total charge is 0. So you can work out the formula of an ionic compound by balancing the charges on its ions.

1. Write down the name of the ionic compound.
2. Write down the symbols for its ions.
3. The compound must have no overall charge, so balance the ions until the positive and negative charges add up to zero.
4. Write down the formula without the charges.