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Explain giving justification the trends in the following properties of elements, on moving from left to right in a period, in the Modern periodic Table:
(a) Variation of valency.
(b) Change of atomic radius.
(c) Metallic to non-metallic character.
(d) Electronegative character.
(e) Nature of oxides.
Answer
(a) Valency
Valency and valence electrons are the same till the number of outermost electrons is 4. After that, valency is 4 minus the number of outermost electrons.
Therefore, as we move from left to right in a period, the valency first increases then decreases .
(b) Atomic radius
As we move from left to right in a period, the e ffective nuclear charge increases because the number of protons increases and due to this the electrons come closer to the nucleus and atomic radii decrease .
(c) Metallic character
It is the ability of an atom to donate electrons . From left to right, effective nuclear charge increases which means that the electrons are held strongly by the nucleus and their donation becomes difficult.
Therefore, metallic character decreases.
On the other hand, non metallic character i.e. the ability to accept electrons increases.
(d) Electronegative character
Electronegativity is the ability of an atom to attract a shared pair of electrons towards itself . From left to right as the effective nuclear charge increases and electronegativity also increases.
(e) Nature of oxides
As we move from left to right, the metallic character decreases and non metallic character increases.
Metals form basic oxides and non-metals form acidic oxides.
So, the oxides are basic towards the left but keep becoming acidic when we move toward the right.
