Trends in electronegativity

Question 1

What is electronegativity?

Answer 1

It is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Question 2

What is the general trend for electronegativity on the periodic table?

Answer 2

The values of electronegativity decrease down the groups in the periodic table and increase across the periods.

Question 3

Why do the values of electronegativity decrease down the groups in the periodic table? (2)

Answer 3

1. Increasing atomic radius:
   The atomic radius increases down the groups.
   The outermost electrons are becoming further away from the attractive force of the nucleus. Therefore, there is a smaller attraction between the nucleus and the shared pair of electrons.
2. Screening effect of inner electrons:
   The nuclear charge increases down the groups, this is cancelled out by the screening effect of the intervening energy levels of electrons.
   The outermost electrons are shielded from the attractive force of the positively charged nucleus.
   The attraction of the nucleus to the outermost electrons decreases going down the group.

Question 4

Why do the values of electronegativity increase across a period in the periodic table? (2)

Answer 4

1. Increasing effective nuclear charge:
   The number of protons in the nucleus is increasing. The attraction between the nucleus and the outer electrons is steadily increasing. The electrons involved in bonding are being more strongly attracted to the nucleus.
2. Decreasing atomic radius:
   The atomic radius decreases from left to right. The electrons in the outermost level are becoming closer to the nucleus. There is a greater attraction between the nucleus and these outer electrons and the electronegativity increases.