Electronegativity Values (College Board AP® Chemistry): Revision Note

Electronegativity values

• Electronegativity is the tendency of an atom to attract a pair of electrons when it forms a covalent bond, mainly involving valence electrons

• Electronegativity generally increases across a period

  • Since the number of protons increase, there effective nuclear charge increase

  • This makes the Coulombic attraction between the nucleus and the electrons from the covalent bond stronger

  • Therefore, the electronegativity value will increase

Change in electronegativity across a period

Electronegativity increases going across the periods of the periodic table

• Down a group, electronegativity decreases

  • The main responsible is the increase in the shielding effect

  • Since the distance between the nucleus and the valence electrons increases, the Coulombic forces attraction are considerably weaker

  • In consequence, the effective nuclear charge decreases, the electrons from a covalent bond are weakly attracted, and the electronegativity value decrease

Change in electronegativity down a group

Electronegativity decreases going down the groups of the Periodic table

• The Pauling scale has the values of electronegativity for each atom

  • Noble gasses does not appear in the Pauling scale since they do not form covalent bonds because of their full valence shell

The Pauling scale

First three rows of the periodic table showing electronegativity values

• Fluorine (F) is the most electronegative atom in the periodic table

  • It is the best when attracting electron density towards itself when it forms a covalent bond with an atom

Molecule of CH₃F

Electron distribution in the C-F bond of fluoromethane