Bond Types and Intermolecular Forces

Introductory Chemistry - molecular structure modelBond types help explain the relationship between two atoms within a molecule. There are four key types of bonds:

  • Non-polar
  • Polar covalent
  • Ionic
  • Metallic

These bonds are categorized based on the difference in electronegativity (an atom’s ability to attract an electron). In the periodic table, the least electronegative element is in the bottom left hand corner (Francium) and the most electronegative is in the top right hand corner (Fluorine) if you exclude the noble gases. Non-polar bonds are between two elements with no electronegativity difference. Polar covalent bonds are between two atoms that have different electronegativity values but they are below about 1.8 difference on the Pauling scale.

Ionic bonds are characterized by two atoms that have an electronegativity difference of greater than 1.8. Metallic bonds occur primarily amongst transition metals and can be described as a sea of electrons. In these bonds between each atom of the transition metal, the electrons are flowing and shared throughout the group.

Intermolecular forces (IMFs) are the interactions that occur between molecules because of charges on atoms. These forces are a weaker attraction than a bond, but they do influence properties of the pure substance or solutions. The main types of intermolecular forces are:

  • Hydrogen bonding
  • Dipole-dipole
  • Van der Waals Forces

Hydrogen bonding is a special type of IMF that only occurs between hydrogen and nitrogen, oxygen, or fluorine. These bonds are the strongest of the intermolecular forces due to the relatively small size of hydrogen and the high electronegativity of nitrogen, oxygen, and fluorine. Dipole-dipole forces are weaker than hydrogen bonding and are a result of a permanent shift in charges on atoms in a molecule. Van der Waals Forces are weaker than dipole-dipole forces and are a result of non-permanent shifts in charges on atoms.