Elements, Compounds and Mixtures

All substances are made of atoms - until now we called them particles. There are only about 100 different elements, but there are thousands of different chemicals. Most chemicals are made up of a combination of elements and we call these compounds. Two or more atoms joined together are known as a molecule.

	A substance that is made of only one sort of atom is called an
	are made up of two or more elements held together by chemical bonds. All the molecules must be the same.
	are a collection of different types of atoms and molecules that are not chemically bonded

All the elements (and nothing else) are shown in the periodic table. The columns are called , they contain elements with chemical properties. Each element is represented by a chemical , normally from the latin for the element.

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Use the periodic table to fill in the symbols for the following elements:

Element	Symbol
Carbon
Calcium
Oxygen
Hydrogen

The formula of a compound shows the number and type of atoms that are joined together to make the compound. For example Water has the chemical formula H₂O. This means that it has two hydrogen atoms joined to one oxygen atom in each molecule.

Atoms themselves have a small central nucleus around which there are electrons orbiting: