Atoms, Elements, Compound and Mixtures

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Everything is made from atoms.

Atoms are tiny particles far to small to see, even with a microscope

If people were the same size as atoms, the entire population of the world would fit into a box about a thousandth of a millimetre across

We usually imagine atoms as being tiny balls

To make things simpler we draw atoms as tiny balls.

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Elements:

There are over 100 drifferent elements.

The atoms in a particular element are the same as each, and they are drifferent from the atoms of all other elements

E.g. lead and gold are elements

A piece of pure lead only contains lead atoms

The atoms of some elements don't join together, but instead they stay as separate atoms.

Helium is like this.

The other elements e.g. hydrogen and oxygen, form together to make molecules.

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Mixtures:

A mixture is elements that are not all chemically combined with each other.

They can be seperated

They are not pure

Compounds:

A compound is a substance that contains atoms of two or more different element chemically joined together.

Eg. Water is a compound of Hydrogen and Oxygen

Each of its molecules contains two hydrogen atoms and one oxygen atom. There are a lot of different compounds

Each element is given its own chemical symbol, like H for hydrogen or O for oxygen

Each chemical symbol starts with a capital letter, with the 2nd letter in lower case

E.g. Mg is the correct symbol for Magnesium, not MG, mG, MG

It is sometimes easy to tell the chemical symbol of the element, but sometimes it is hard

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Chemical formulae:

For a molecule, we use the chemical symbols of the atoms it contains to write down its formula

E.g. The formula for carbon monoxide is CO

It tells you that each molecule of carbon consist of one Carbon atom joined with one oxygen atom.

Be careful about use of caps.

e.g. CO means molecule of carbon monoxide but Co is the symbol for cobalt (an element)

Formulae is the plural of formula

We use numbers to show when a molecule contains more than one atom of an element

The numbers are written before the element symbol. e.g. CO2(UNDER)

Some formulae are more complicated.

E.g. sodium sulphate is Na2SO4

The formula for a substance is always the same

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