CHEM EXAM 4

Valence Bond Theory

• electron density of the valence electrons is localized between bonding atoms

• Located in half filled orbitals that overlap to form molecular bonds

Molecular Orbital Theory

• the electron density of valence electrons is delocalized within the molecule

• Occupy molecular orbitals that spread throughout entire molecule

Valence electrons of the atoms in a molecule reside in

Quantum-mechanical atomic orbitals (s, p, d, f orbitals)

Number of standard atomic orbitals added together equals

The number of hybrid orbitals formed

Combinations of standard atomic orbitals added together determine

Shapes and energies of the hybrid orbitals formed

The type of hybridization that occurs is

The one that yields the lowest overall energy for the molecule

Sigma Bond

• electron density between two atoms

• Can be formed from hybridization or unhybridized atomic orbitals

• Single bonds

Pi Bonds

• electron density found above and below plane of the bond

• Formed from unhybridized p or d orbitals

• Double bonds have one

• Triple bonds have two

Paramagnetic

• Magnetic properties

• If MO diagram has unpaired electrons

Diamagnetic

• no magnetic properties

• If MO diagram had all paired electrons

Bond order =

# of bonding electrons - # of antibonding electrons / 2

Intermolecular forces

Weak attractions between molecules

Ion ion attractions

• ionic compounds

• Cation and anions

• Metal and non metal

• Strongest and highest melting/boiling point

Dipole dipole interactions

Polar molecule interactions

Hydrogen bonding

Type of dipole dipole only possible if H is bonded to F, O, or N

Dispersion forces

• weakest force

• Only force of attraction for Nonpolar molecules

Higher the mass

Stronger the intermolecular force (if they are from the same species)

Surface tension

A liquids resistance to increase in its surface area

Decreased Surface Tension

Increased temperature

The stronger the intermolecular force

The greater the energy required to increase the liquids surface area/tension

Capillary Action

Spontaneous rising of a liquid through cohesive and adhesive forces

Cohesive Forces

Hold liquid molecules together

Adhesive Forces

Attract the outer molecules of the liquid to the containers inner surface

Viscosity

Measure of a liquids resistance to flow

As Viscosity decreases

Temperature increases

As viscosity increases

The size of the molecule increases

Solubility

Like dissolves like

Ionic compounds will dissolve in

Polar solvents

Rate of Vaporization increases

Temperature increases

Rate of vaporization increases

Surface area increases

Rate of vaporization increases

Decreased intermolecular strength

Condensation is an

Exothermic process

Vaporization is an

Endothermic process

Dynamic Equilibrium

When two opposite processes reach the same rate so that there is no gain or loss of material

Boiling point

Vapor pressure = external pressure

Higher boiling point

Stronger intermolecular force

Evaporation

Liquid to gas

Condensation

Gas to liquid

Sublimination

Solid to gas

Deposition

Gas to a solid

Molecular solids

Covalent compounds

Ionic solids

Ionic compounds/ cation and anion

Nonbonding atomic solid

Noble gases

Metallic atomic solids

Metals

Network covalent atomic solids

Diamond, graphite or quartz

Amorphous solids

• Plastic or glass

• No regular geometric pattern over a long range

Solvent

Component in larger amounts

Solute

Component in a smaller amount

For solute and solvent to mix

Must overcome all solute-solute attractive forces and some solvent-solvent

When delta H solution is positive

Indicates endothermic process

When delta H solution is negative

Indicates Exothermic process

Solubility can be expressed as

Grams of solute/ 100 grams of Water

Unsaturated

• Solvent contains less than the maximum amount of solute

• Under the line

Saturated

• Solvent contains the maximum amount of a solute at a specific temperature

• On the line

Supersaturated

• solution contains more solute than is supposed to be possible for a given quantity of a solvent

• Over the line

Solubility increases in solids and liquids with

Increasing temperatures (endothermic)

Solubility decreases in gases with

Increasing temperatures (Exothermic)

Nonelectrolytes

• 1 mole will equal 1 particle ( “i” = 1)

• Covalent compounds

Strong electrolytes

1 mole will equal 2 or more particles of the mole (“i” is greater than or equal to 2)

Osmosis

Passage of solvent molecules from a less concentrated solution to a more concentrated solution

The level of the solution with the higher solute concentration will

Rise

Hypertonic

• Higher concentration

• Higher osmotic pressure

Hypotonic

• Lower concentration

• Lower osmotic pressure

Hemolysis (Hypotonic)

RBCs swell and may burst

Crenation (hypertonic)

RBCs will shrink in size