12.1 Intramolecular Forces “Within” the molecule and are called covalent and ionic bonds. Molecules are formed by sharing electrons between the atoms. Covalent bonds hold the atoms of a molecule together. Ionic bonds hold oppositely charged ions together in a formula unit

12.1 Intermolecular Forces Forces that occur between molecules. Intramolecular (ionic and covalent) bonds are stronger than intermolecular forces.

12.6 Intermolecular Forces There are two kinds of intermolecular forces that occur between molecules. Dipole–dipole forces (between polar molecules) Hydrogen bonding (between hydrogen of one polar molecule and O, N, F of another polar molecule) London dispersion forces (between nonpolar molecules)

12.6 Dipole–Dipole Attraction Polar molecules contain different atoms which have different electronegativity's and can be thought to be like a small bar magnet. Oppositely charged ends attract and like ends repel. Molecules organize themselves to maximize the attractive forces and minimize repulsive forces giving molecules unique shapes.

12.6 Hydrogen Bonding Strong dipole-dipole forces. Hydrogen is bound to a highly electronegative atom – nitrogen, oxygen, or fluorine.

12.6 Hydrogen Bonding in Water Blue dotted lines are the intermolecular forces between the water molecules.

12.6 London Dispersion Forces Become stronger as the sizes of atoms or molecules increase.

Ion Dipole Forces Ion Dipole forces are typically found in aqueous solutions of ionic compounds, such as salt water. In the figure below the nonbonding electrons found on the oxygen atom are strongly attracted to the sodium ion.

Overview of Particle Forces Type of Force Relative Strength Present in Examples Dispersion Force (London Force) Weak, increasing with size atoms/molecules H2 (g) Polar molecules HCl Dipole-dipole force moderate Molecules with hydrogen bonded to N,O, or F Hydrogen bond Strong HF, NH3, H2O Ion-dipole Very strong Mixtures of ionic and polar compounds Na+,Cl-, and H2O