Everything Science Grade 10

2.4 CHAPTER 2. CLASSIFICATION OF MATTER

Step 2:Write down the charges on the ions

The sodium ion has a charge of+1and the fluoride ion has a charge of

− 1.

Step 3:Find the right combination

For every plus, we must have a minus. So the+1from sodium cancels

out the− 1 from fluoride. They combine in a1 : 1ratio.

Step 4:Write the formula

NaF

Example 4: Writing chemical formulae 2

QUESTION

What is the formula for magnesium chloride?

SOLUTION

Step 1:List the ions involved

Mg2+and Cl−

Step 2:Find the right combination

Magnesium has a charge of+2and would need two chlorides to bal-

ance the charge. They will combine in a 1:2 ratio. There is an easy way

to find this ratio:

Mg2+

Cl−

2

1

Draw a cross as above, and then you can see that Mg→ 1 and

Cl→ 2.

Step 3:Write down the formula

MgCl 2

38 Chemistry: Matter and Materials