1. Phase Changes and Intermolecular Forces

2. Phases of Matter All matter is made of tiny solid particles—known as atoms— at the microscopic level. At the macroscopic level (much bigger) matter is either a solid, liquid, or a gas The phase of matter (solid, liquid, gas) is dependent on the motion and spacing of the particles

3. Phases of Matter Solid: particles move very slowly in place; they occasionally slide past one another Solids have a definite shape and a definite volume Liquid: atoms move more freely and more quickly than they do in solids Liquids have a definite volume and an indefinite shape Gas: atoms move even more freely and more quickly than they do in liquids Gases have an indefinite shape and volume

5. Intramolecular vs. intermolecular forces Intramolecular forces are the forces within a molecule that keep it together Ionic or covalent bonds Intermolecular forces are the forces between molecules; responsible for keeping matter in either the solid, liquid, or gas phase

6. Phase Changes When intermolecular forces are very strong, matter will be in the solid phase When energy (heat) is added, the particles begin to break free from some of the forces and move more quickly— become a liquid When enough energy is added, the particles can break free from all intermolecular forces—become a gas Temperature causes the phase changes because at a higher temperature, particles will have greater energy and move more quickly

7. Vaporization and evaporation are not the same Vaporization requires that you heat the substance to its boiling point Evaporation can occur at much lower temperatures

8. Warming is adding heat, cooling is the removal of heat Temperature remains constant when heat is added until the phase change is complete

9. Four types of Intermolecular Forces (IMF) Ionic forces: attraction between charged atoms or molecules Very high boiling point Hydrogen bonding: a hydrogen atom bonds to either nitrogen, oxygen, or fluorine High boiling point, but not as high as ionic Van der Waals: differences in electronegativity Weaker than hydrogen bonds, therefore a lower boiling point We will discuss electronegativity in length tomorrow London Dispersion: weakest of all IMF, everything has at least London forces Boiling point increases with weight; bigger molecules have higher boiling point