Year 7 Science · Unit 2 · Lesson 15

Chemical Formulas and Naming

Foundation Worksheet

Name

Date

Class

Learning Goals

Read subscripts in chemical formulas to count atoms of each element.
Identify the seven diatomic elements and their formulas.
Name binary compounds using the -ide rule (e.g. NaCl = sodium chloride).

Warm Up

Fill the gap

Choose the correct word from the word bank to complete each sentence. Two words will not be used.

formula subscript diatomic chloride oxide binary mixture element

A chemical uses element symbols and numbers to show what atoms are in a substance. The small number written after an element symbol is called a — it tells you how many atoms of that element are present. Elements like O₂ and H₂ are called elements because they naturally exist as two-atom molecules. A compound made of exactly two different elements is called a compound. When naming these compounds, the second element's name gets an "-ide" ending: for example, the compound NaCl is called sodium , and MgO is called magnesium .

Your Turn

Sort it!

Write each formula from the pool into the correct category box.

NaCl O₂ MgO H₂ CaF₂ N₂ CO₂ Cl₂ AlCl₃ Br₂

Binary compound (two different elements bonded)

Diatomic element (single element, pairs)

Show What You Know

1. Write the name of each compound using the -ide naming rule: (a) MgO (b) HCl (c) CaS

Recall 3 marks

2. In the formula H₂O, how many atoms of hydrogen are present? How many atoms of oxygen? How many atoms are there in total?

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?