Chapter 1: Structure Determines Bonding

Answers to Questions relating to Bonds and Bond Polarity

1.  What types of bond exists between the atoms in a molecule of methyl lithium, CH₃Li ?

The formula for this compound can be written as [CH₃^-][Li⁺] because the metal is very electropositive compared  to the carbon atom  (if we look at their electronegativities, C = 2.5, Li = 1.0).  The [CH₃^-] group, a methyl anion, has covalent bonds between carbon and hydrogen.  Though there is no significant bond polarity to a C-H bond there is a molecular polarity to the anion because of the negative charge placed on carbon.  The attraction of the Li⁺ cation to CH₃^- is essentially ionic.

The formula for this compound can be written as [Na⁺]₂[SO₄^2-], the sulfate anion is formed by covalent bonding between sulfur and oxygen.  Since there is a bond polarity to a S-O bond these are polar covalent bonds.  The attraction of the Na⁺ cations to SO₄^2- is ionic.

 A non-polar covalent bond exists between the atoms in a molecule of Cl₂.

The structure is shown as the resonance hybrid (so both O atoms have equal partial -ve charges).  The most significant polar bonds are the CO bonds.  Since H and C have very similar electronegativities (2.2 and 2.5 respectively), the CH bonds are essentially non-polar.