Question

Write scientific reasons.
a. Atomic radius goes on decreasing while going from left to right in a period.
b. Metallic character goes on decreasing while going from left to right in a period.
c. Atomic radius goes on increasing down a group.
d. Elements belonging to the same group have the same valency.
e. The third period contains only eight elements even through the electron capacity of the third shell is 18 .

Answer 1

a. Atomic radius goes on decreasing while going from left to right in a period because atomic number of the elements increases which means the number of protons and electrons in the atoms increases(the extra electrons being added to the same shell). Due to large positive charge on the nucleus, the electrons are pulled closer to the nucleus and the size of an atom decreases.

b. Metallic character goes on decreasing while going from left to right in a period because the tendency of atoms of the elements to lose electrons(or gain electrons) changes in a period. As we move from left to right in a period, the nuclear charge increases due to gradual increase in the number of protons. Due to the increase in nuclear charge, the valence electrons are pulled strongly by the nucleus and it becomes difficult for the atoms to lose electrons. Hence, metallic character decreases.

c. Atomic radius increases as we move from top to bottom in a group of the periodic table because a new shell of electrons is added to the atoms at every step. As the number of shells in the atoms increases gradually due to which the size of atoms also increases. As the size of the atoms increases which leads to increase in atomic radius of an atom.

d. Elements belong to the same group have the same valency because the number of valence electrons in a group is same due to which the tendency of an atom to lose or gain electrons in order to attain nearest noble gas configuration is also same.

e. The third period contains only eight elements even through the electron capacity of the third shell is 18 because when the other shells get filled and the resultant no of electrons becomes eighteen, it gets added up and settles in the third electron shell and three shells is acquired by fourth period.