Liquids Solids Vocab you need to know Intramolecular

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

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

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

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

What type(s) of intermolecular forces exist between each of the following molecules? HBr is a polar molecule: dipole-dipole forces. There also dispersion forces between HBr molecules. CH 4 is nonpolar: dispersion forces. SO 2 O SO 2 is a polar molecule: dipole-dipole forces. There also dispersion forces between SO 2 molecules. 11. 2

Concept Check Which molecule is capable of forming stronger intermolecular forces? N 2 H 2 O Explain. Copyright © Cengage Learning. All rights reserved 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

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

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

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 Copyright © Cengage Learning. All rights reserved 18

Heating Curve for Water Copyright © Cengage Learning. All rights reserved 19

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) Copyright © Cengage Learning. All rights reserved 20

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 21

Classification of Solids Copyright © Cengage Learning. All rights reserved 22

Network Solids Copyright © Cengage Learning. All rights reserved 23

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 emobile “sea” of e- 11. 6