Unit 3 - Chemistry

Intermolecular

Attraction between molecules

IMF

Breaking - physical change

MUCH WEAKER THAN INTERMOLECULAR

Intramolecular

Attraction within the molecule

Covalent bond

Breaking - chemical change

MUCH STRONGER THAN INTERMOLECULAR

Why are boiling points the best measure of IMFs?

Boiling (gas) → severing the IMFs

Ion-dipole

Attraction between an ion and a polar molecule  

Ion-Dipole and Coulomb’s Law

Ion-Dipole - Force of increases a

CHARGE OF ION INCREASES

RADIUS OF ION DECREASES

DIPOLE ON THE POLAR MOLECULE INCREASES

F = kQ1Q2/d²

Dipole-Dipole

Attractive force between more negative end of one polar molecule or the same molecule

Orientation and Dipole-Dipole

Positive and negative dipoles line up IN POLAR SOLID

IN NON POLAR SOLID there is less order since there is less attraction

Hydrogen Bonding 

A dipole-dipole attraction

2 REQUIREMENTS

1. H covalently bonded to F,O,N

2. F,O, or N on another molecule with at least 1 lone pair

   ALSO OH works 

   INTERMOLECULAR FORCE

Strength (order) for bonds

LDFs <Dip-dip< H-bonding

Why is H bonding so strong?

F,O,N atom is pulling so hard on the electrons shared H very positive

More electrons (TOTAL NOT JUST VALENCE)

Higher Boiling Points from stronger IMFs

Dipole- Induced Dipole

When a non-polar species is polarized by another polar molecule

STRONGER WHEN THE POLAR MOLECULE HAS A LARGER DIPOLE MOMENT

THE NONPOLAR MOLECULE HAS A LARGER ELECTRON CLOUD (more polarizable) 

LDFs

all species of atoms have LDFs, due to temporary skewing of electron cloud, instantaneous charge distributions are polar 

Polarizable 

The more electrons a species has the stronger LDFs - therefore the more polarizable 

LDFS increase as the

contact area between molecules increases

order of intermolecular forces of attraction

LDFs, dipole-induced dipole, ion-induced dipole, dipole-dipole, H-bonds, ion-dipole, ion-ion

Vapor Pressure

The inverse of boiling point, HIGHER BP = LOWER VP

Ionic Solids

Most are soluble in polar solvents

CONDUCT ELECTRICITY ONLY WHEN MOLTEN OR DISSOLVED

charged particles/Mobile

THE HIGHER THE CONCENTRATION OF IONS IN THE SOLUTION, THE HIGHER THE ELECTRICAL CONDUCTIVITY (e.g. distilled water)

How to figure out how conductive a compound would be when dissolved

HIGHEST CHARGE, BUT ENSURE IT IS SOLUBLE FIRST

Ionic Solids part 2

Very strong Coulombic Attraction between ions

High Melting Point

Very Hard, Low Volatility 

Molecular solids

Do not conduct electricity

No charged particles

EXCEPTIONS: acids can conduct 

HELD TOGETHER BY IMFs

Heat of fusion

Energy required to break IMFS of 1 MOLE to go from a solid to a liquid

Heat of vaporization

Energy required to break IMFs of 1 MOLE to go from liquid to gas

Heat of Vaporization

Ionic Compounds require much MORE ENERGY

Molecular Liquids

IMFs can be strong — but not as strong as in solids more freedom to move

The heat absorbed as 1 mole of liquid becomes gaseous 

USED TO BREAK IMFS

always endothermic

IDEALLY NO IMFs attraction in gases 

Boiling Points pt 2

A liquid boils when its vapor pressure equals the atmospheric pressure, separates molecules from eachother, BUT STAY IN TOTAL COMP.

Boiling points decrease as…

ELEVATION INCREASES

Covalent Network Solid

Composed of 1 or 2 NON METALS

Network of covalent bonds 

CARBON GROUP - due to 4 valence electrons

VERY HIGH MP, VERY HARD, FIXED ANGLES

Metallic Solids

Between nuclei and delocalized valence electrons

Mobile

NOT IONIC OR COVALENT 
NEUTRAL ATOMS

Metallic Bonding

Nuclei and core e are localized, valence e are mobile

CONDUCT HEAT + ELECTRICITY 

MALLEABLE AND DUCTILE 

Alloys

Interstitial

MORE RIGID

LESS MALLEABLE

LESS DUCTILE 
REMAINS CONDUCTIVE 

Substitutional 

REMAINS MALLEABLE AND DUCTILE
REMAINS CONDUCTIVE 

COLOR CHANGES

Particulate Characteristics of Solids

Motion is limited — vibration

Close together

Held together by IMFs/Chemical Bonds

Structure is influenced by the ability of the particle to pack together 

Amorphous Solids

Random arrangement, no orderly structure

Macroscopic structure lack well defined faces/shapes

Many are mixtures of molecules

Crystalline solids

Atoms, ions, molecules arranged in crystal lattice

• Macroscop

Liquids

Particles move and collide with one another

Movement is influenced by strength of IMF and temperature

Particles are very close together

Very small difference from solid

Great difference from gas 

Volume of Solids and Liquids

Similar molar volumes

Densities are close

Most solids have slightly smaller molar volume than their liquid

Ice has slightly larger molar volume than liquid water

Pressure

Caused by gas particles colliding with container wall P = F/A

Gasses exert pressure in ——-

all directions

Boyle’s Law

Relationship between pressure and volume of gases

VOLUME IS INVERSELY PROPORTIONAL 

Temperature

A measure of the average kinetic energy of atoms or molecules 

Kelvin Temp is proportional to KE

Charles’ Law

Relationship between Temperature and Volume of Gases

V1/T1 = V2/T2

PROPORTIONAL RELATIONSHIP

Properties of a gas

Particles are constantly moving

They expand to fill the volume of their container

Form homogeneous mixture

Low density

Highly compressible

Exert a pressure 

Collision Frequency and Density depend on

Pressure

Volume

Temperature

1 mole will occupy

22.4 L at STP, (1 mole is 6.022 ×10²3 particles)

Dalton’s Law of Partial Pressures

P total = P1 + P2 + P3

Combined Gas Laws

PV/T initial = PV/T final

Mole Fraction

Xa = Moles of one compound/ SUM OF ALL MOL COMPONENTS 

Find Partial Pressure of any gas by multiplying total pressure by its

mole fraction

Ideal Gas Law assumes the V of gas particles is (KINETIC MOLECULAR THEORY)

0, Coulombic forces do not exist, KE is conserved by elastic collisions, AVERAGE KE IS PROPORTIONALTO ABSOLUTE TEMPERATURE 

KE of Gas Particles

Translational energy

Particles move through space in straight lines ** MOST OF A GAS PARTICLE’S KE

Rotational energy

Vibrational Energy

Maxwell-Boltzmann Distribution 

KE increases as T increases, larger range of kinetic energies larger pressures

Deviations from Ideal Gas Law

All Real Gases DO NOT Behave Ideally when Under HIGH P

OR at LOW T

V adjustment for Gases Under High Pressure

Ideal gas equation assumes that molecules do not have their own volumes

V in PV = nRT is the volume of empty space in the container

The volumes of gas particles are negligible when compared to the overall volume of the container at relatively low pressure This is due to the fact that they are very small and very far apart 

At High P, molecules are compressed into a much smaller volume of space and the volue occupied by the molecules becomes significant 

P adjustment for gases under high P (low V)

When gas particles are very close together, the pressure exerted may be less that what the ideal gas equation would predict

Neighboring molecules exert forces of attraction on one another when they are very close together

Such forces pull a gas molecule in the direction opposite to its motion

This reduces the pressure resulting from impacts with the walls of the container 

Gases do not behave ideally at low T 

ideal gas law assumes that gases experience no intermolecular forces of attraction

At High T, the KE of gas particles overcome any IMF

At Low T, gas particles move slower and are closer together

Attractions between molecules exist under these conditions 

Non Ideal Behavior and Condensation

Increase as the distance between particles decreases 

This can lead to condensation at sufficiently low T or very high P

This applies to all gases, even those with relatively weak IMFs

When a gas is approaching the point where condensation will occur, the forces of attraction are at a maximum

This results in the largest possible decrease in measured pressure, and therefore a large deviation from ideal behavior

Suspension

A heterogeneous mixture of 2 or more substances

Macroscopic properties are different at different locations within the sample

Solution of Homogeneous Mixture

A mixture of 2 or more substances

Macroscopic properties do not vary within the sample

Components cannot be separated by filtration 

Components can be separated by methods that alter IMFs

Components are larger enough to scatter the light 

Solvent

Thee substance that is more plentiful in a solution

Solute

The substance that is less plentiful in a solutions

Types of solutions

Liquid-Liquid, Solid-Liquid (polar solvents most of the time), Gas-Liquid, Gas-solid, Solid-Solid

Like dissolves

Like (Solubility), HIGHER TEMPERATURE INCREASE SOLUBILITY (except with gases)

Pressures only applies to gas-liquid solutions

If cation-anion attractions are stronger than the ion-dipole attraction,

the compound will not be soluble

How to determine solubility in water

charges, lower charges = higher likelihood of solubility

Filtration

Particle Size

Distillation

boiling points

Chromatography

polarity

Concentration

M = mol solute/L of soln.