definition of size of atom and how it will vary group and period
Answers
Radius of an atom is the distance from the centre of the nucleus to the valence electron of the atom.
1) Along a group: The atomic radius increases from top to bottom in a group due to addition of new shell.
2) Along a period: The atomic radius decreases from left to right in a period because of increasing effective nuclear charge.
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Answer:
(1) In a period : Atomic radius decreases in a period from left to right (upto group 17). This is because as we move across a period, nuclearncharge increases but electrons enter the same shell. Thus, the screening effect of the inner core remains the same. As a result the valence electrons are tightly held by the nucleus and atomic size (radius) decreases. For example, in 2nd Period, it decreases from Li(152 pm) to F(64 pm).
(2) In a group : Down the group, as the atomic number increase, nuclear charge increses but number of shells increase. As a result, shielding effect increases and valence electrons are held by weaker attrctive forces. Thus, atomic radius increases. For example, atomic radius increases. For group 17 elements, the value increase from 1st member F (64 pm) to the last member At (140 pm).