Covalent Bonds in Polymers (Cambridge (CIE) AS Biology): Revision Note

Covalent bonds in polymers

• A covalent bond is the sharing of two or more electrons between two atoms

  • The electrons can be shared equally forming a nonpolar covalent bond or unequally (where an atom can be more electronegative δ^-) to form a polar covalent bond

• Generally, each atom will form a certain number of covalent bonds due to the number of free electrons in the outer orbital e.g. H = 1 bond, C = 4 bonds

• Covalent bonds are very stable as high energies are required to break the bonds

• Multiple pairs of electrons can be shared forming double bonds (e.g. unsaturated fats C=C) or triple bonds

• When two monomers are close enough that their outer orbitals overlap this results in their electrons being shared and a covalent bond forming

  • If more monomers are added then polymerisation occurs (and a polymer forms)

Condensation

• A condensation reaction occurs when monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed

Hydrolysis

• Hydrolysis means ‘lyse’ (to break) and ‘hydro’ (with water)

• In the hydrolysis of polymers, covalent bonds are broken when water is added

Organic Molecules	Covalent Bonds	Diagram of Covalent Bonds
Carbohydrates	Glycosidic
Proteins	Peptide
Lipids	Ester
Nucleic Acids	Phosphodiester