Polarity of Covalent Bonds

Covalent bonds share electrons (ionic bonds transfer electrons) Bonding electrons (shared pairs of electrons between elements) are pulled on (like in a tug-of-war) as atoms compete for the electrons

Electronegativity Values Refer to p. 161 in your textbook

Polar Molecules A polar molecule is created when electrons are shared unequally in a molecule. The electrons are held closer to the more electronegative atom than they are to the less electronegative atom This causes part of the molecule to be slightly negative, and the other part to be slightly positive.

Electronegativity Determines Polarity Each atom has an electronegativity value which corresponds to how strongly it attracts electrons. Polarity is determined by the difference in the electronegativity values of atoms that make up a molecular compound.

Determining Polarity… Step 1: Find the electronegativity values of the atoms that make up the molecule (look at an electronegativity table, p. 161 in your textbook) Step 2: SUBTRACT the value of the less electronegative atom from the value of the more electronegative atom.

Non-polar covalent difference = 0.0 – 0.3 Polar Covalent Ionic difference > 1.7 Polar-covalent

HCl H – Cl for example… electronegativity 2.1 3.0 value difference 0.9, a POLAR covalent molecule **Chlorine is stronger than H (3.0>2.1) and therefore pulls the shared electrons closer to the Cl atom, inducing a negative charge at its pole – H therefore acquires a positive charge, hence, a POLAR molecule +H :Cl -