Atoms, Elements, Compounds, Mixtures State of matter

1. Solid, Liquid or Gas?
You need to
remember which
of the first 20
elements are
gasses, and which
are liquids

2. Compounds and Mixtures
• All substances are either elements, compounds or
mixtures.
• An element is made up of only one type of atom.
Carbon and oxygen are both elements.
• A compound is a substance made up of two or more
elements joined together. For example, when carbon
atoms join with 2 oxygen atoms, they form a
compound called carbon dioxide.
• Carbon atoms that are just mixed with oxygen atoms,
but are not attached to them, form a mixture. A
mixture can also contain compounds, if they are not
joined to the other substances in the mixture.
• For example, air is a mixture of elements such as
nitrogen and oxygen, and compounds, such as water
and carbon dioxide.

3. “Stable”
atoms/elements?
Atoms are more stable energetically when
they have eight electrons in their valence
shell, the outermost electron shell.
Atoms ‘want’ a full outer shell of electrons,
i.e. they are most stable with a full outer shell.
This explains why the Group 8 elements, the
noble gases, do not react to make compounds
— they are already as stable as they can be