Electronegativity & Bonding (Cambridge (CIE) AS Chemistry): Revision Note

Using Electronegativity to Predict Bond Formation

• The differences in Pauling electronegativity values can be used to predict whether a bond is covalent or ionic in character

Electronegativity & covalent bonds

• Single covalent bonds are formed by sharing a pair of electrons between two atoms

• In diatomic molecules, the electron density is shared equally between the two atoms

  • Eg. H₂, O₂ and Cl₂

• Both atoms will have the same electronegativity value and have an equal attraction for the bonding pair of electrons leading to the formation of a covalent bond

• The equal distribution leads to a non-polar molecule

Electronegativity and non-polar molecules

Electronegativity & ionic bonds

• When atoms of different electronegativities form a molecule, the shared electrons are not equally distributed in the bond

• The more electronegative atom (the atom with the higher value on the Pauling scale) will draw the bonding pair of electrons towards itself

• A molecule with partial charges forms as a result

• The more electronegative atom will have a partial negative charge (delta negative, δ^-)

• The less electronegative atom will have a partial positive charge (delta positive, δ⁺)

• This leads to a polar covalent molecule

Electronegativity and polar covalent molecules

• If there is a large difference in electronegativity of the two atoms in a molecule, the least electronegative atom’s electron will transfer to the other atom

• This in turn leads to an ionic bond – one atom transfers its electron and the other gains that electron

  • The cation is a positively charged species which has lost (an) electron(s)

  • The anion is a negatively charged species which has gained (an) electron(s)

Electronegativity and ionic bonding