Unit 3 APCHEM

INTRAmolecular bonding

the sharing/transfer of electrons

INTERmolecular bonding

the interactions between particles (atoms, molecules, ions)

What causes state changes?

Changes in intermolecular forces

True or false: Intermolecular bonding isn’t actual bonding

True

5 types of intermolecular forces

• Dipole-dipole attractions

• Ion-dipole attractions

• London dispersion forces

• Dipole induced dipoles

• Ion induced dipoles

Order intermolecular forces from weakest to strongest

• London dispersion forces

• Dipole induced dipoles

• Ion induced dipoles

• Dipole-dipole attractions

• Ion-dipole attractions

Dipole

Molecule with one partially negative and one partially positive pole separated by distance

Dipole-dipole attractions

Polar molecules’ partial charges are attracted

Molecules orient themselves to… (list 2)

1. Minimize repulsion

2. Maximize attraction

Hydrogen bonding

strong dipole-dipole attraction where a Hydrogen is bonded to F,O,N

Why are hydrogen bonds so strong?

• High polarity = stronger attraction

• H is small which allows closeness

• There is a big electronegative difference

Ion-dipole attractions

Attraction between ion and polar molecules

True or false: all dipoles are polar

True

Which is stronger: dipole-dipole or ion-dipole attractions

Ion-dipole

London dispersion forces (LDFs)

weak forces that exist between noble gases and non-polar molecules

True or false: LDFs are seen in everything

True

Why do LDFs occur?

Temporary dipoles

Temporary dipoles

electron imbalances lead to more electrons on one end than the other, leading to partial negativity and partial positivity

How do temporary dipoles effect nearby molecules?

causes a chain reaction

Dipole induced dipoles

A polar molecule (permanent dipole) causes a non-polar molecule to polarize, creating a temporary dipole

Ion induced dipoles

An ion polarizes a non-polar molecule, creating a temporary dipole

Why are attractions involving ions stronger than ones with just dipoles?

Dipoles have a partial charge, whereas ions have a full charge

2 classifications of solids

• Amorphous solids

• Crystalline solids

Amorphous solids

twisted, long chains of molecules; disordered

Crystalline solids

highly organized arrangement of components called a “crystal lattice”

Which solid is the strongest?

Crystalline solids

Ionic solids

ion latice held by Coulombic attraction; low vapor pressures, high MP/BP

When do ionic solids conduct electricity?

When ions are mobile (e.g. when melted or dissolved)

Example of ionic solid

NaCl

Molecular/covalent solids

nonmetal and metal lattices, held by LDF or dipole-dipole attractions; low melting point, no electric conductivity

What is different about the covalent bondings in molecular solids?

strong bondings within molecules, but weak intermolecular bonding

Example of molecular solid

Sucrose

Metallic solids

cation lattices, held by metallic bonds

Example of metallic solid

gold

Covalent network solid

atoms at each lattice point, covalent bonds lead to one large molecule; high MP, poor conductivity

What group of elements are associated with covalent network soilds?

Group 4

Order attractions by strength (weakest to strongest)

• LDF

• Dipole-dipole

• Hydrogen bonding

• Non-polar covalent

• Polar covalent bonding

• Metallic bonding 

• Ionic bonding

• Covalent network solid

True or false: metals have a higher MP/BP than ionics

True

Solid

definite, vibrates in space, tightly packed

Liquid

definite volume, takes shape of container, flowing particles, more spacious than solids

Gas

takes volume/shape of container, particles in constant motion, far apart

Surface tension

a liquid’s resistance to an increase in surface area

Viscosity

a liquid’s resistance to flow

Describe the relation between intermolecular forces, surface tension, and viscosity

Direct

Why are complex molecules more viscous?

Because they tangle up

Endothermic

absorbs heat

Exothermic (think: exit)

releases heat

Vaporization

endothermic process where energy is absorbed and added to break intermolecular bonding

Heat of vaporization

energy required to vaporize a mole of a liquid at 1 atm

Describe the relation between intermolecular forces and heat of vaporization

Direct

Condensation

gaseous molecules/vapor reform a liquid

When is the system at a dynamic equilibrium?

when rate of condensing = rate of evaporating

Vapor pressure

pressure of vapor at equilibrium

Characteristics of a volatile liquid

• Evapores rapidly

• High vapor pressure

What affects vapor pressure & relation

• Molar mass (inverse)

• Intermolecular forces (inverse)

Heating curve

graph of temperature vs. time

What do the

Phase change

Heat of fusion

enthalpy change when solid melts

Relation between intermolecular forces and heat of fusion

direct

Normal melting point

temperature when solids/liquids have same vapor pressure at 1 atm

Normal boiling point

temperature when the vapor pressure of liquid is exactly 1 atm

Relation between intermolecular forces, melting point, and boiling point

Direct

Melting point of noble gases

low

Freezing point when we go down the noble gas group

Decreases

LDF when we go down the noble gas group

Increases

What is directly related to intermolecular forces?

Everything but vapor pressure

Properties of gas

compressible, uniformly fills containers, easily mixes with other gases

Diffusion

mixing of gases

Effusion

passage of a gas through a tiny orifice into an evacuated chamber

Relation between gas weight and rate of effusion/diffusion

Direct

Molar volume

2.24 L of an ideal gas at STP

STP conditions

273.15 K and 1 atp

Units of pressure

atm, mm Hg/torr, pa

How much mmHg is equal to 1 atm?

760

What unit of temperature is used in calculations?

Kelvin

Combined gas law equation

P₁V₁ = P₂V₂

n₁R₁T₁ n₂R₂T₂

What is R when we’re dealing with atm?

0.08206

What is R when we’re dealing with kPa?

8.314

Molecular weight formula

mass (g)/n

Density formula

mass/V

Pressure formula using density and molecular weight

P = dRT/MW

Mole fraction

ratio of moles of a compound in a mixture to total moles in mixture

Partial pressure

mole fraction * total pressure

Pressure formula from Dalton’s Law

P_gas = P_total - P_H2O

4 things the Kinetic Molecular Theory of Gases states

1. volume of gases are negligible (0)

2. particles are in constant motion, collisions caused by pressure

3. particles do not attract or repel each other

4. kinetic energy is proportional to Kelvin of gas

Relation between Kelvin and and motion of gas particles

Direct

Pressure formula

P = sum of particles’ forces striking container walls/surface area in container

Relation between temperature and range of velocities

Direct

Boltzmann Distribution graph

shows speed of gases at a given temperature

Relation between temperature and Boltzmann Distribution curve height/peak

Inverse

When does a gas act most ideally?

Low pressure, high temperatures

As you cool a gas toward condensation temperature…

there are higher attractions between particles

Solute

substance that dissolves

Solvent

substance that does the disolving

Homogenous mixtures

uniform

Heterogenous mixtures

properties vary depending on location

Why is water the universal solvent?

• bent/polar

• electrons unevenly shared = polar

• hydration

• H₂O dissolves polar covalents

Hydration

ionic compounds dissolve

Electrolytes

solutions with extra ions that conduct electricity better

Strong electrolyte-a

highly conductive solution that easily conducts electrical current