Liquids & Solids

Vocab you need to know: Intramolecular forces Intermolecular forces dipole-dipole forces ion-dipole forces london dispersion forces hydrogen bonding Viscosity Surface tension Cohesive forces Adhesive forces Heating curve Heat of fusion Heat of vaporization Critical temperature Critical pressure Vapor pressure Boiling point solids (molecular, covalent-network, ionic, and metallic)

Intramolecular Bonding “Within” the molecule. Molecules are formed by sharing electrons between the atoms. Copyright © Cengage Learning. All rights reserved 3 3

Solids & Liquids Caused by intermolecular forces (IMF) Higher IMFs lead to higher melting points of solids and higher boiling points of liquids IMFs in order of decreasing strength: Hydrogen bonding (strongest) (broken bone) Ion-dipole forces (tore ACL) dipole-dipole forces (sprained ankle) London dispersion forces (weakest) (paper cut)

Hydrogen Bonding really strong type of dipole-dipole force exists only when hydrogen is bonded to F, O, or N (H-NOF) accounts for water’s really high boiling point (compared to other molecular compounds) and the fact that water expands when it freezes and its high surface tension

Hydrogen Bonding Copyright © Cengage Learning. All rights reserved 6 6

Dipole Forces Ion-dipole forces exist btwn ions and polar molecule enables some salts (ions) to dissolve in water (polar) Dipole-dipole forces exist btwn separate polar molecules dipole of one molecule attracts the dipole of another molecule

Dipole-Dipole Forces Copyright © Cengage Learning. All rights reserved 8 8

London Dispersion Forces caused by induced (temporary) dipoles exist for ALL atoms and molecules, but is only observable in non-polar molecules atoms with higher amounts of electrons are more easily polarized and thus have stronger LD forces

London Dispersion Forces Copyright © Cengage Learning. All rights reserved 10 10

What type(s) of intermolecular forces exist between each of the following molecules? HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules. CH4 CH4 is nonpolar: dispersion forces. S O SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules. 11.2

Concept Check Which molecule is capable of forming stronger intermolecular forces? N2 H2O Explain. H2O has the stronger intermolecular forces because it exhibits hydrogen bonding, whereas N2 only exhibits London dispersion forces. Copyright © Cengage Learning. All rights reserved 12 12

Liquid Properties Viscosity – resistance to flow, increases with molar mass Surface tension – caused by imbalance of IMFs at the surface of a liquid Cohesive forces – bond to itself (like water molecules to themselves) Adhesive forces – bond to something else (like water to glass tubing), causes a meniscus

attracted to each other Properties of Liquids Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules Adhesion attracted to glass Cohesion attracted to each other 11.3

Melting and Boiling Points In general, the stronger the intermolecular forces, the higher the melting and boiling points. Copyright © Cengage Learning. All rights reserved 15 15

The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A, 5A, 6A, and 7A Copyright © Cengage Learning. All rights reserved 16 16

Phase Changes heating curves (we did one in earlier this semester) heats of fusion (solid liquid) and vaporization (liquid gas) are the flat parts of a heating curve nonpolar substances tend of have low critical temps and polar substances tend to have high critical temps (because of difference in IMFs)

Vapor Pressure measure of how many molecules are in the gas phase vs. liquid/solid phase in a closed system higher vapor pressures correspond to lower molar masses and weak IMFs Increasing temp increases vapor pressure the temperature when atmospheric pressure equals vapor pressure is the boiling point of a liquid (normal bp is temp at which vapor pressure equals 1 atm)

Changes of State 19 Copyright © Cengage Learning. All rights reserved

Heating Curve for Water Copyright © Cengage Learning. All rights reserved 20 20

A convenient way of representing the phases of a substance as a function of temperature and pressure: Triple point Critical point critical temperature (Tc) - temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. critical pressure (Pc) - minimum pressure that must be applied to bring about liquefaction at the critical temperature. Phase equilibrium lines Copyright © Cengage Learning. All rights reserved 21 21

Phase Diagram

Concept Check As intermolecular forces increase, what happens to each of the following? Why? Boiling point Viscosity Surface tension Enthalpy of fusion (solid to liquid) Freezing point Vapor pressure Heat of vaporization (liquid to gas) Boiling point increases Viscosity increases Surface tension increases Enthalpy of fusion increases Freezing point increases Vapor pressure decreases Heat of vaporization increases Copyright © Cengage Learning. All rights reserved 23 23

Types of Crystalline Solids Ionic Solids – ions at the points of the lattice that describes the structure of the solid. Ion-ion is strong than all IM forces Atomic Solids – atoms at the lattice points that describe the structure of the solid. Stronger than IM forces but generally weaker than ion-ion Molecular Solids – discrete covalently bonded molecules at each of its lattice points. Held together with only IM forces Copyright © Cengage Learning. All rights reserved 24 24

Classification of Solids Copyright © Cengage Learning. All rights reserved 25 25

Network Solids Copyright © Cengage Learning. All rights reserved 26 26

Cross Section of a Metallic Crystal Types of Crystals Metallic Crystals – Typically weaker than covalent, but can be in the low end of covalent Lattice points occupied by metal atoms Held together by metallic bonds Soft to hard, low to high melting point Good conductors of heat and electricity Cross Section of a Metallic Crystal nucleus & inner shell e- mobile “sea” of e- 11.6