Atoms, elements and compounds, Year 8: more practice

Hydrogen, sulfur and oxygen

提示Match each capital letter to an element.

为什么H is hydrogen, S is sulfur and O is oxygen. The small number 2 tells you there are two hydrogen atoms.

One carbon atom and one oxygen atom

提示A missing number never means none.

为什么If no number follows a symbol, there is just one atom of that element. CO is carbon monoxide.

Sodium chloride

提示The name of the metal comes first, then the non-metal with its ending changed.

为什么Two elements join, so the name of the second one ends in -ide: chlorine becomes chloride.

Potassium, sulfur and oxygen

提示The ending -ate tells you about an extra element.

为什么Names ending in -ate hide oxygen. Potassium sulfate is made of potassium, sulfur and oxygen.

Copper sulfate

提示Compare the endings of the four names.

为什么The others end in -ide and each has just two elements. Copper sulfate contains copper, sulfur and oxygen, which is why its name ends in -ate.

2

提示An -ide ending tells you how many elements there are.

为什么The ending -ide means a compound of just two elements. Here they are zinc and sulfur.

9

提示The 3 in front multiplies the whole of H2O.

为什么One H2O has two hydrogen atoms and one oxygen atom, which is 3 atoms. Three of them make 3 × 3 = 9.

An element

提示Count how many different kinds of circle there are.

为什么Only one type of particle is present, so it is a single element. A compound would show different circles joined together.

A mixture

提示Look for any joins between the different circles.

为什么Two substances are present but not chemically bonded, so it is a mixture of two elements.

Many

提示Think of the word 'polygon'.

为什么A polymer is made of many repeating small units joined in a long chain. Poly- is also in polygon and polythene.