On a basic level, the atomic mass tells you the number of protons an element has. It's elements in the same groups or periods that have similar properties i.e elements in the same group or period as Na will have similar properties; same for Ne
Sodium:
- group 1: 1 electron on outermost shell
- alkali metal,
- highly reactive because it can easily lose the electron on it's outer shell
- one electron on outermost shell.
- Period 3 (3 orbitals/shells)
Neon:
- Group 8: 8 electrons on outermost shells; all paired up
- noble gas,
- inert/unreactive because it's hard to get rid of all 8 electrons on outer shell compared to the 1 e Na has
- period 2 (2 orbitals/shells)
