Atoms

Have a radius of 0.1 nanometers 

Nucleus

- Contains protons and neutrons

- Middle of the atom

- Positive charge

- Almost all the atom's charge is concentrated here

Electrons

- Move in shells

- Negatively charged 

- Volume of their orbits determines the size of the atom. Have virtually no mass.

Nuclear symobl = Tells you atomic (proton) number and mass number

Atomic number = How many protons there are

Mass number = Total number of protons and neutrons

To get the number of neutrons in an atom subtract the atomic number from the mass number.

Atoms are NEUTRAL - They have the same number of of protons as electrons

The charge on the electrons is the same size as the proton charge but opposite, so they cancel out.

In an ion, the number of protons and electrons aren't the same. This means they have an overall charge. An ion is an atom or group of atoms that have lost or gained electrons.

PARTICLE       MASS       CHARGE

Proton                 1                  +1

Neutron               1                   0

Electron               0                  -1

The electron's mass is very very small so is often written as 0