The variation in the size of atom of the element belonging to same period and same group in term of electronic configuration
Answers
The electron arrangements of atoms help explain the properties of elements and the structure of the periodic table. When substances react, it is only the outer electrons in the atoms that are involved - the nature of the reactions which occur depend upon the number of outer shell electrons in the reacting atoms
Lets talk about the 3rd group.
In the 3rd group the first element is Na - 2,8,1
the next one is Mg - 2,8,2 and so on...
Since with increase in no. of protons with the increasing atomic no. in a particular period the attraction by the protons towards the electrons increases. Hence the electrons are more tightly bound to the atom and hence the size decreases. This is the reason why with increasing atomic no. size of the atom goes on decreasing in a particular period.