2.1.1

# Atomic Model

Test yourself

## Atomic Model - Example

An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.

## Size of Atoms vs Nucleus

Atoms have a radius of about 1 × 10-10 metres. However, the nucleus of atoms are even smaller.

### Atoms

• If an atom was the size of Wembley Stadium, then...

### Nucleus

• ...its nucleus would be the size of a garden pea!

## The Charges and Masses of Sub-Atomic Particles

The 3 different sub-atomic particles (protons, neutrons and electrons) have different relative charges and masses. Atoms have no overall charge (are neutral). In an atom, these charges all cancel each other out.

### Protons

• Protons have a relative charge of +1.
• In SI units, this is +1.60 × 10-19C.
• They are found in the nucleus.
• An element’s atomic number is the number of protons it possesses.
• All atoms of the same element have the same number of protons.
• Protons have a relative atomic mass of 1.
• In SI units, this is 1.67 × 10-27kg.

### Electrons

• Electrons have a relative charge of -1.
• In SI units, this is -1.60 × 10-19C.
• They are found in fixed orbits around the nucleus.
• In any atom, the total number of negative electrons equals the number of positive protons, meaning atoms have no overall electric charge.
• Electrons have a relative atomic mass of 1/2000.
• In SI units, this is 9.11 × 10-31kg.

### Neutrons

• Neutrons have a relative charge of 0 - they are neutral.
• Like protons, they are found in the nucleus.
• Neutrons have a relative atomic mass of 1 (the same as a proton).