Matter Let’s get to the heart of it… The particles are in constant motion
Kinetic-Molecular Theory Describes the motion of individual molecules Kinetic = “to move” Also called Kinetic Theory
Forces of Attraction Affect on States of Matter At room temperature (20 o C-25 o C, 68 o F-77 o F) all particles of matter have the same kinetic energykinetic energy So why do we have different states of matter for these materials? There are different strengths of INTERMOLECULAR FORCES
13.2 Forces of Attraction Intermolecular Forces What holds molecules together
Intermolecular Forces They are what make solid and liquid molecular compounds possible. The weakest are called van der Waal’s forces - there are two kinds Dispersion forces (London forces) Dipole Interactions
Dispersion Force Depends only on the number of electrons in the molecule Bigger molecules more electrons More electrons stronger forces F 2 is a gas Br 2 is a liquid I 2 is a solid All are nonpolar but why are they different states of matter?
Dispersion Force Occurs between all molecules Depends only on the number of electrons in the molecule Result from a temporary shift in density of electrons in electron clouds Causes nonpolar molecule to become polar Happens quickly and temporarily for nonpolar molecules
Dipole interactions Occur when polar molecules are attracted to each other. Slightly stronger than dispersion forces. Opposites attract but not completely hooked like in ionic solids.
Dipole interactions Occur when polar molecules are attracted to each other. Slightly stronger than dispersion forces. Opposites attract but not completely hooked like in ionic solids. HFHF HFHF
Hydrogen bonding Are the attractive force caused by hydrogen bonded to F, O, or N. F, O, and N are very electronegative so it is a very strong dipole. Causes hydrogen to have a large partial positive charge on it The molecules are small, so they can get close together The hydrogen partially share with the lone pair of electrons on an atom in a neighboring molecule The strongest of the intermolecular forces.
Hydrogen Bonding H H O ++ -- ++ H H O ++ -- ++
Hydrogen bonding H H O H H O H H O H H O H H O H H O H H O
Hydrogen bonding is the reason why water has unique properties compared to other molecules its same size Properties: It is a liquid at room temp. It is a good solvent It is less dense as a solid (ice floats) Just remember Water is not the only molecule that has hydrogen bonds.
Examples: What type of intermolecular forces do the following molecules have? NH 3 O 2 CO 2 HBr Which of the following compounds can form dipole-dipole forces: Cl 2, CO, NO, CH 4 Hydrogen bonding Dispersion forces Dipole-dipole forces
13.4 Phase Changes What is a phase? The distinct states of matter when they are in mixtures How is this different from just states of matter? Occur due to changes in temperature.
Phase changes that need energy Melting Heat of Fusion Melting Point KMT?
Vaporization Heat of Vaporization How is this different from evaporation? KMT?
Properties of Molecules Most have LOW melting & boiling points tend to be gases and liquids at room temperature Ex: CO 2, NH 3, H 2 O Polar and Nonpolar molecules have a little bit different properties due to the partial charges.
Properties of Solid Molecules Two kinds of crystals: Molecular solids – molecules held together by attractive forces Ex: BI 3, Dry Ice, sugar Network solids- atoms held together by bonds One big molecule (diamond, graphite) High melting & boiling points, brittle, extremely hard