1) As you go down the group from Lithium
to francium, overall the atomic radius of the atoms increases
and additional electron shells are added. This means that
the outer most electron is further away from the positive
centre of the nucleus. This decreases the proton-electron
pull making it easier to remove the outer electron. The
inner electron shells also shield the outer electron from
the positive protons in the nucleus.
2) The answer to this question lies in the
electronic configuration. The p-orbital holds 6 electrons,
phosphorous has 3 electrons in it, so it is half full. 1
in each of Px, Py and Pz. The next atom along which has
one more electron sulphur. This additional electron would
have to go into one of these three, meaning that one set
of electrons would have formed pairs. Due to a repulsion
energy between this pair of electrons it need less energy
to remove one of them and hence this is why the ionisation
energy for sulphur is lower than that for phosphorous.
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