In which of the following sets elements have nearly same atomic radii and why??
a)Fe,Co,Ni,Cu
b)O,S,Se,Te
c)Mg,Ca,Cr,Ba
d)Li,Be,B,C
The correct option is a)Fe,Co,Ni,Cu.
Reason-
The atomic radii decreases across the period. The atomic size decreases because the new electron enters the same d orbital each time the nuclear charge increases by unity. Also the shielding effect of a d electron is not that effective, hence the net electrostatic attraction between the nucleus and the outermost electron increases and the atomic radius decreases. However, after manganese, the atomic radii are almost comparable. This is because up till manganese, the d-orbitals are half filled. After manganese, the electrons are added to the d-orbitals which are already occupied by one electron. This results in repulsion. Thus there are two effects acting in the opposite direction, the inter electronic repulsion and the attraction between the nucleus and the outermost electron. Because of this the atomic radii of the d-block are almost same from Mn to Cu.
Reason-
The atomic radii decreases across the period. The atomic size decreases because the new electron enters the same d orbital each time the nuclear charge increases by unity. Also the shielding effect of a d electron is not that effective, hence the net electrostatic attraction between the nucleus and the outermost electron increases and the atomic radius decreases. However, after manganese, the atomic radii are almost comparable. This is because up till manganese, the d-orbitals are half filled. After manganese, the electrons are added to the d-orbitals which are already occupied by one electron. This results in repulsion. Thus there are two effects acting in the opposite direction, the inter electronic repulsion and the attraction between the nucleus and the outermost electron. Because of this the atomic radii of the d-block are almost same from Mn to Cu.