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Unit 1 - fundamentals of science


17/09

Chemistry
● Protons, +1 relative mass 1
● electron, -1 relative mass 1/1840
● Neutron, 0 relative mass 1

In each element, there is the
● Mass number - no. of protons and neutrons
● Atomic number - no. of protons which is equal to
the amount of electrons.




element protons neutrons electrons Mass no. Atomic no.

hydrogen 1 0 1 1 1

aluminium 13 14 13 27 13

titanium 22 26 22 48 22

krypton 36 48 36 84 36

Oxygen -16 8 8 8 16 8

Oxygen -18 8 10 8 18 8



Levels and sub-levels

The Aufbau principle states that the lowest energy sub-levels are occupied first.

There are four sublevels labelled in order of increasing energy, each holds a different number of
electrons.
● S
● P
● D
● F

, Unit 1 - fundamentals of science




This is in order of lowest to highest and represents the different levels and sublevels.




sublevel Max no of electrons it can hold

S 2

P 6

D 10

F 14