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ICSE - X - Chemistry

While moving across a period in a periodic table,the atomic size decreases.In books the reason is that , while moving across a period proton number increases.So,the nucleus attracts the electrons with greater force.But,my query is that besides proton number,electron munber also increases while moving across a period and also the charge of a proton is equal to charge of a an electron.So,the increasing proton number must be nullified by increasing electron number.Thus,the atomic size must be same while moving across a period.But,it is not so.Please,explain!

Asked by ayan 31st March 2017, 9:31 AM
Answered by Expert


Atomic size gradually decreases from left to right across a period of elements. Because, within a period or family of elements, all electrons are added to the same shell. But, at the same time, protons are being added to the nucleus, making it more positively charged. Effect of increasing proton number is greater than that of the increasing electron number; So, there is a greater nuclear attraction. This means that the nucleus attracts the electrons more strongly, pulling the atom's shell closer to the nucleus. The valence electrons are held closer towards the nucleus of the atom. As a result, the atomic radius decreases.

Answered by Expert 31st March 2017, 5:39 PM

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