Periodicity

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Periodicity

Periodic table: arranges elements by proton no.

-all elements within a period have same number of e- shells

-all elements within a group have the same no. of e- in their outer shell (so have similar properties)

-group no. tells you no. of e- in outer shell (apart from group 0)

using table to work out e- configurations:

split into s, d, p and f-block

-now easy to find e- structure

e.g. phosphorous: 1s(2)2s(2)2p(6)3s(2)3p(3)

atomic radius decreases across a period

1. as no. of p+ inc, +ve charge of nuc inc - thf e- are pulled closer to nuc, making atomic radius smaller

2. extra e- that elements gain are added to the outer energy level, so they don't really prove any extra shielding effect