There are three differnet parts of an atom:

• Protrons - relatively large with a positive charge.
• Neutrons - approx. same mass as protrons with no charge.
• Electrons - extremely small with a negative charge.

• Contains the protons and neutrons.
• Makes up most of the atom's mass.
• Makes up small part of the atom's volume.

• Empty space where electrons orbit nucleus at a high speed.
• Large part of the atom's volume.
• Subdived into Energy Levels (or Shells).
• Electrons fill lower energy levels first and move outward.
• This formula can be used to determine how many electrons call fill a given shell: where n = electron level; maxmium number of electrons = 2n².

This table shows the maximum number of electrons for the first four enegy levels:

Energy Level	Max. No. of electrons
1	2
2	8
3	18
4	32

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