Chemistry - elements, mixtures and compounds

Chemistry - elements, mixtures and compounds
Substances can be (1) pure elements, (2) pure compounds or (3) mixtures of elements or compounds.

Atoms
All substances are made of atoms. An individual atom is too small to see, so everything around you contains very many atoms.
If an element is divided into smaller and smaller pieces, an atom is the smallest part that can exist.

Elements
An element is a substance that is made of only one sort of atom. Oxygen is an element because it contains only oxygen atoms.
There are about 100 different elements. Atoms of each element are given a chemical symbol.
Every symbol starts with a capital letter, often followed by a lower case letter. For example, N represents a nitrogen atom, but Na represents a sodium atom.
•The elements are shown in the periodic table.

Compounds
Compounds form when atoms of different elements are combined during a chemical reaction. Compounds can separate back into elements only through chemical reactions.
The different elements combined in a compound are in fixed proportions, shown in the chemical formula.
Example
H20
The formula of every water molecule is H20 because in each molecule two hydrogen atoms are chemically combined with one oxygen atom.

Mixtures
A mixture consists of two or more elements and/or compounds. These components are not chemically bonded. The chemical properties of each component in the mixture remain unchanged.
Worked example
Some iron powder and some sulfur powder are mixed, and tested with a magnet. The mixture is heated and cooled. The product is then tested with the magnet.
Explain why the magnet attracts some of the mixture before heating, but none of the product after heating.
(2 marks)
The magnet attracts the iron, which is magnetic.
When the mixture is heated iron sulfide is formed, which is non-magnetic.
In the mixture, iron retains its magnetic property,