Melting Point and Boiling Points of Ionic and Covalent Compounds According to Kinetic Molecular Theory Particles in solids vibrate As temperature increases, vibration increases If the particles gain enough kinetic energy they can break apart from neighbouring particles When particles have enough energy to break away, the melting point has been reached Higher melting point – attraction between particles is higher.

Boiling Point and Kinetic Molecular Theory In liquids, particles have enough energy to break away from neighbouring particles, but they are attracted to other particles At the boiling point – particles have enough kinetic energy to break away from all other particles and become a gas. High boiling point – forces b/n particles are strong Low boiling point – forces b/n particles are weak

Melting Points and Boiling Points Compound Melting Point (°C) Boiling Point (°C) ethanol , C2H5OH -114 +78.3 ammonia, NH3 -77.7 -33.3 cesium bromide, CsBr +636 +1300 hydrogen, H2 -259 -253 hydrogen chloride, HCl -85 magnesium oxide, MgO +2825 +3600 methane, CH4 -182 -161 nitrogen, N2 -210 -196 sodium chloride, NaCl +801 +1465 water, H2O +100 Classify each into 1 of 3 categories: Low, intermediate or high boiling point.

Melting Points and Boiling Points Compound Melting Point (°C) Boiling Point (°C) ethanol , C2H5OH -114 +78.3 ammonia, NH3 -77.7 -33.3 cesium bromide, CsBr +636 +1300 hydrogen, H2 -259 -253 hydrogen chloride, HCl -85 magnesium oxide, MgO +2825 +3600 methane, CH4 -182 -161 nitrogen, N2 -210 -196 sodium chloride, NaCl +801 +1465 water, H2O +100 Classify the bonds in each of the molecules as covalent, polar covalent or ionic.

How is bond type related to boiling point? Look at the results of your 2 lists. How do they compare? What does this tell you about the relative bond strength of each type of bond? Explain your results by referring to the Kinetic Molecular Theory

Types of Forces Between Particles Attractive Electrostatic Forces – occur b/n ions of opposite charge  they are strong Dipole-dipole Forces – occur between the positive end of one molecule and the negative end of another  happens in polar molecules  weak London Dispersion Forces – occur between any 2 molecules. Caused by the random movement of electrons...this creates temporary dipoles  very weak