State all the exceptions to the general trend of screening effect with reasons.

1)By normal trend atomic radius increases along a period however the atomic radius of noble gases is fgreter than the adjacent halogen atom. This is because noble gas atoms are held together by van der waal forces (which are weaker and hence the atoms are apart from each other) while the halogen atoms are bound together by covalent bonds which are much stronger than the van der waal forces and hence held the atoms closer..2)d block contraption; The cause of the d-block contraction is the poor shielding of the nuclear charge by the electrons in the d orbitals. The outer valence electrons are more strongly attracted by the nucleus causing the observed increase in ionization potentials. The d-block contraction can be compared to the lanthanide contraction which is caused by inadequate shielding of nuclear charge by electrons occupying f orbitals.

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