Question

Between the fifth and sixth period, there is an especially large increase in the density of transition metals in the same group. There are two physical reasons for this

observation. Carefully explain both of these reasons.

(I only know that it's the intro of the lanthanide group.)

Answer 1

Between the fifth and sixth period, there is an especially large increase in the density of transition metals in the same group because:

(a)filling of electron in 4 f and 5f orbital and these orbital have poor shielding of nuclear charge so  6s electrons are pull  towards the nucleus, so atomic radius decreases. we know

density = mass/volume

therefore atomic density increases.This is also called lanthanide contraction.

(b)In any period when we move left to right in periods number of orbit not change but nuclear charge increases therefore atomic size decreases and atomic density increases.

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