Liquids & Solids. Vocab you need to know: Intramolecular forces Intermolecular forces – dipole-dipole forces – ion-dipole forces – london dispersion forces

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)

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Intramolecular Bonding

• “Within” the molecule.• Molecules are formed by sharing

electrons between the atoms.

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

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

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

SO

O

What type(s) of intermolecular forces exist between each of the following molecules?

HBrHBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.

CH4

CH4 is nonpolar: dispersion forces.

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.

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

11.3

Adhesion is an attraction between unlike molecules

Adhesion

Cohesion

attracted to glass

attracted to each other


Melting and Boiling Points

• In general, the stronger the intermolecular forces, the higher the melting and boiling points.


The Boiling Points of the Covalent Hydrides of the Elements in Groups

4A, 5A, 6A, and 7A

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


Heating Curve for Water


• 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

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)


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


Classification of Solids


Network Solids

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

11.6

Cross Section of a Metallic Crystal

nucleus &inner shell e-

mobile “sea”of e-

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Liquids & Solids. Vocab you need to know: Intramolecular forces Intermolecular forces – dipole-dipole forces – ion-dipole forces – london dispersion forces