2. Atoms
All substances are made of ATOMS.
Water – hydrogen and oxygen atoms
Plastic – carbon and hydrogen atoms
Plants – carbon, nitrogen, hydrogen, oxygen and
sulfur atoms
3. Elements
• There are about 100 substances that are made
up of just one type of atom.
• These are elements.
Helium
Carbon
Copper
4. Molecules
• In some elements, the atoms are joined in
groups of two or more – this is called a
molecule.
O2
Other elements that contain atoms joined in
molecules are hydrogen, nitrogen, chlorine and
bromine.
5. Symbols for Elements
H – Hydrogen
C – Carbon
F – Fluorine
O – Oxygen
N – Nitrogen
I – Iodine
Li – Lithium
Al – Aluminium
He – Helium
Pb – Lead
Au – Gold
Ag - Silver
6. Compounds
• A compound is the substance produced when
two or more elements combine in a chemical
reaction – they are also molecules.
H2O
CO2