Question

Why is Fr the least electronegative element?

Answer 1

The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity. It is a dimensionless property because it is only a tendency. It basically indicates the net result of the tendencies of atoms in different elements to attract the bond forming electron pairs. We measure electronegativity on several scales. The most commonly used scale was designed by Linus Pauling. According to this scale fluorine is the most electronegative element with a value of 4.0 and Fransium is the least electronegative element with a value of 0.7.

Electronegativity of elements depends on the following factors:

1. Size of an atom: A greater atomic size will result in less value of electronegativity, this happens because electrons being far away from the nucleus will experience lesser force of attraction.
2. Nuclear charge: A greater value of nuclear charge will result in greater value of electronegativity. This happens because increase in nuclear charge causes electron attraction with greater force    There is an increase in atomic number as we move down the group in the modern periodic table. Nuclear charge also increases but the effect of increase in nuclear charge is overcome by the addition of one shell. Hence the value of electronegativity decreases as we move down the group. For example, in the first group the value decreases as we move from lithium downwards to francium.