Unit 11: States of Matter

Ch. 13, Sections 2-4

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Types of Covalent Bonds

• Polar Covalent Bond– e- are shared unequally– asymmetrical e- density– results in partial charges (dipole)

• Nonpolar Covalent Bond– e- are shared equally– symmetrical e- density– usually identical atoms

Types of Covalent Bonds

If ΔEN is: Bond type is:

< 0.4 Nonpolar covalent

0.4 < Δ EN < 1.7 Polar covalent

> 1.7 Ionic

Given: Electronegativities of these elements

H = 2.2 C = 2.55 N = 3.04 O = 3.44 F = 3.98Na = 0.93K = 0.82 P = 2.19 S = 2.58 Cl = 3.16

Determine bond type for the following bonds:

H – H _____________________ H – O ________________________H – C _____________________ Na – Cl ________________________C – Cl _____________________ F – F ________________________K – F _____________________ H – N ________________________

Take the absolute value of the difference!

Intermolecular Forces (IMF)Intermolecular Forces (IMF)

• Attractive forces between molecules.

• Much weaker than

chemical bonds

within molecules.

• a.k.a. van der Waals forces

Types of IMFTypes of IMF

• London dispersion forces– Exist in all atoms and molecules

(temporary dipoles)– Attraction between two

instantaneous dipoles– Weakest– Larger the molecule, larger the

dispersion force.

Types of IMFTypes of IMF

• London Dispersion Forces

View animation online.

Types of IMFTypes of IMF

-Dipole-Dipole forces

-Attraction between two permanent dipoles

-Polar molecules

-Medium strength

-Stronger when molecules are closer together

Types of IMF Types of IMF

• Dipole-Dipole Forces

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View animation online.

Types of IMFTypes of IMF

• Hydrogen bonding– Special kind of dipole-

dipole– Occurs between

molecules that have an H bonded to either O, N, or F.

– Extremely polar bonds– Strongest– Not chemical bonding

Types of IMFTypes of IMF

• Hydrogen Bonding

Types of IMF• The hydrogen bonds in water explain its relatively high boiling

point, considering that it is a small molecule. The H-bonds hold the water molecules together as a liquid, so you have to heat it a lot before it will change to a gas. Compare boiling points of these molecules:

Molecule IMF (s) present Molar Mass (g/mol)

Boiling Point (oC)

CH4 16.05 - 164

HCl 36.46 - 85

H2O 18.02 100

London Disp.

London Disp.

Dipole-DipoleLondon Disp./Dipole-Dipole/Hydrogen Bonding

Properties of Liquids

• Density:– Higher in liquids than gases

• Intermolecular forces hold liquid particles together• Gas particles are far apart and have minimal

attraction between particles.

• Compressibility:– Only slightly in liquids

• Molecules already closely packed• Gases have a lot of empty space between particles

and can be compressed.

Liquid PropertiesLiquid Properties

• Viscosity– Resistance to flow

Viscosity Demo

Liquid PropertiesLiquid Properties

• Surface Tension– attractive force between particles in a liquid that

minimizes surface area

Action of detergents:• Detergents are used to clean dirt/oil from clothing, dishes, etc. • How does this work?

– The detergent interacts with water in such a way that the hydrogen bonding is disrupted, and this breaks the surface tension of the water, so that the dirt can mix with the water. Detergents are called surfactants, because they are surface active agents.

• Detergents have a special structure that aids the cleaning process. A micelle is formed when detergents interact with dirt/oil and water. – Water is polar. – Dirt and oils are nonpolar.– Detergents are long molecules that have polar “heads” and

nonpolar “tails”. – “like dissolves like”

• Because detergents have a dual nature, they can dissolve grease and carry it away in the water at the same time.

Cohesion and Adhesion

• Cohesion is the force of attraction between identical molecules in a liquid (cohesion is a result of intermolecular forces).

• Adhesion is the force of attraction between liquid molecules and a solid that is touching them.

Liquid PropertiesLiquid Properties• Capillary Action

– attractive force between the surface of a liquid and the surface of a solid

water mercury

Meniscus of water in a glass tube is concave: adhesion > cohesion

Meniscus of Hg in a glass tube is convex: cohesion > adhesion

PROPERTIES OF SOLIDS

• Density: In general, the particles of a solid are more closely packed than those of a liquid. So most solids are more dense than most liquids, but there are exceptions (wax, cork). When solid and liquid states of a substance coexist, the solid is more dense than the liquid, so the solid will sink in the liquid. Water is an important exception (ice floats in water). This is because the H2O molecules are less closely packed in ice than in liquid water.

Types of SolidsTypes of Solids

• Crystalline - repeating geometric pattern– covalent network– metallic– ionic– covalent molecular

• Amorphous –

– no geometric pattern

decreasingm.p.

Crystalline vs. Amorphous:

• A crystalline solid has particles which are arranged in an orderly, geometric, 3-D structure.

– Examples: sodium chloride, ice, gems and minerals

• In an amorphous solid, the particles are not arranged in any particular pattern.

– Examples: rubber, plastics.

Types of SolidsTypes of Solids

CovalentMolecular

(H2O)

CovalentNetwork

(SiO2 - quartz)

Amorphous(SiO2 - glass)

Phase ChangesT

em

pe

ratu

re E. Q=mCΔT

D. Q= mHv Tb B. Q =mHf

C. Q=mCΔTTm A. Q= mCΔT

Thermal Energy (Heat)

Thermal Energy (heat)

• Phase Changes:– B and D represent phase changes– Occur at constant temperature

• Temperature Changes– A,C, and E– Temp is changing– Sloping portion of the graph

Thermal Energy (heat )

• What is happening at each part of the graph:• A. Substance is a solid. Can heat it up or cool it

down along this line.• B. Phase change: solid-liquid. The temperature

at B (Tm) is the melting (freezing) point. • C. Substance is a liquid. Can heat it up or cool it

down along this line.• D. Phase change: liquid-gas. The temperature at

D (Tb) is the boiling (condensation) point.• E. Substance is a gas. Can heat it up or cool it

down along this line.

Heat Calculations

• Q = m c ∆ T– Q = heat or thermal energy in Joules (J) or

calories (cal)– m= mass in grams (g)– C = specific heat in J/(g oC) or cal/(g oC)– ∆T= change in temperature in oC

Heat Calculations

• Q =mHf

– Q = heat or thermal energy in Joules (J) or calories (cal)

– m= mass in grams (g)

– Hf = Heat of fusion (J/g or cal/g); use for liquid-solid phase change

Heat Calculations

• Q =mHv

– Q = heat or thermal energy in Joules (J) or calories (cal)

– m= mass in grams (g)– Hv = Heat of vaporization (J/g or cal/g); use for

gas-liquid phase change

Things to remember

• You can move from left to right or right to left along the curve.

• If you move left to right:– all the processes are endothermic (heat must

be supplied). – Your answer for heat calculations will be

positive.

Things to remember

• If you move right to left:– all the processes are exothermic (heat is

removed/released).

– Your answer for heat calculations will be negative. You need to hand-correct Hf and Hv so they are negative.