Question

How do electronegativity values change in groups & across the periods?

Answer 1

Hint: In a molecule, when some of the electrons are shared between the atoms make up the molecule. When an atom of a molecule having the ability to attract shared electrons is called electronegativity. When there is a higher electronegativity of an atom, there is the greater ability to attract shared electrons. The electronegativity of atoms can be defined in several ways. The widely accepted method is that developed by Linus Pauling.

Complete step-by-step answer:
The electronegativity increases across a period & decreases down to the group. As you go from left to right in the Periodic Table on the same Period, the atomic radii steadily decrease. When the protons are being added to the nucleus, the atomic number increases sequentially, and the nuclear charge increases.

Of course, electrons are also being added to the valence shell, however, because they add to the same shell, they get shielded to each other very imperfectly. Due to this, the electronegativity increases. There is no coincidence that the most electronegative elements occur to be in the right of the Periodic Table.
The order of electronegativity $$N<O<F$$.

On the other hand, the electronegativity decreases as we move down to the group. As we are adding electrons to a new valence shell, the inner shell shields the nuclear charge and the valence shell is farther removed from the nuclear charge. Due to this reason, moving down the Group, electronegativity decreases. The order of electronegativity $$Br<Cl<F$$

Note: The definition of electronegativity states that the ability of an atom in a chemical bond to polarize electron density towards itself. As we move down to the group the energy level increases and the electrons in a bond get farther away from the nucleus so they are held less tightly. So, electronegativity gets decreased.