Chem 2 Exam 1 UARK

VSEPR Theory

helps explain and predict molecular geometry around the central atom

Electron Groups

bonding groups (single, double, and triple bonds each count as one bonding group) and lone pairs of electrons

2 b, 0 lp

Linear

3 b 0 lp

Trigonal planar

2 b 1 lp

Bent

4 b 0 lp

Tetrahedral

3b 1 lp

trigonal pyramidal

2 b 2 lp

bent

5 b 0 lp

Trigonal bipyramidal

4 b 1 lp

Seesaw

3 b 2 lp

T-shaped

2 b 3 lp

Linear

6 b 0 lp

Octahedral

5 b 1 lp

Square pyramidal

4 b 2 lp

Square planar

The 4 most electronegative atoms from highest to lowest

1. F

2. O

3. N/Cl

Most likely result in a non-polar molecule

Linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral

Most likely results in a polar molecule

Bent, trigonal pyramidal, seesaw, t-shape, and square pyramidal

Two geometries that are exceptions and result in nonpolar molecules

Square planar (4 b 2 lp) and Linear (2 b 3 lp)

Solids can be __________

crystalline or amorphous

Amorphous solids have

no long-range order

Crystalline solids have

long-ranger order, regular ordered structure

The changes between states

Intermolecular forces are _______ molecules

BETWEEN

Bonds are _____ molecules

within

Bonds are _____

stronger than intermolecular forces

Dispersion Forces

Between all neutral particles, only intermolecular force between nonpolar molecules

increasing with increasing surface area and size

Dipole-dipole forces

between polar molecules

Hydrogen bonding

between particles w N-H, O-H, F-H bond

strongest intermolecular force in a pure substance

Ion-Dipole force

between polar molecule and ion ex. NaCl (aq)

only occur in mixtures

Hydrogen bonding…

increases the boiling point and melting point of molecules

Like dissolves like, so

polar solvents dissolve polar or ionic solutes

nonpolar solvents dissolve nonpolar solutes

As molar mass increases,

boiling point, melting point, and viscosity increase

As intermolecular forces increase

boiling point, melting point, viscosity, and surface tension increase

Vaporization

the process by which thermal energy can overcome intermolecular forces and produce a state change from liquid to gas

The rate of vaporization increases with

increasing temp, surface area, and decreasing strength of intermolecular forces

Volatile

liquids that vaporize easily

Nonvolatile

liquids that do not vaporize easily

Vaporization is

endothermic (+)

Heat of vaporization of enthalpy of vaporization means

the heat required to vaporize 1 mole of liquid to gas

increases with increasing intermolecular forces

Dynamic equilibrium

rate3 of condensation = rate of vaporization

Vapor pressure

pressure of a gas in dynamic equilibrium with its liquid

depends on temp and intermolecular forces

When a system in dynamic equilibrium is disturbed,

the system responds so as to minimize the disturbance and return to a state of equilibrium

Boiling point

temp at which the liquid’s vapor pressure equals the external pressure

Normal boiling point

the temp a which the vapor pressure equals 1 atm

As elevation increases,

the boiling point of water decreases

Once the boiling point of a liquid is reached,

additional heating only causes more rapid boiling; it does not raise the temp of the liquid above its boiling point

Clausius-Clapeyron equation

compares vapor pressure at two different temperatures

Supercritical fluid

neither a liquid nor gas

Critical temperature

the temp at which the transition to a supercritical fluid occurs T_c

Critical Pressure

the pressure at which the transition occurs P_c

Sublimation

transition from solid directly to gas

ex. dry ice at room temperature

Deposition

transition from gas directly to solid

Melting or fusion

transition from solid to liquid

Freezing

transition from liquid to solid

Heat of fusion, or enthalpy of fusion

the heat required to melt 1 mole of a solid

requires intermolecular forces to be partially overcome

generally increases with increasing intermolecular forces

fusion is positive b/c melting in endothermic

Heating Curve for water

Three main regions of phase diagram

Curves in Phase diagram

Triple point

set of conditions at which three states are equally stable and in equilibrium

Critical point

represents the temp and pressure above which a supercritical fluid exists

If the fusion curve has a positive slope,

the solid state is more dense

If the fusion curve has a negative slope,

the liquid state is more dense

Crystalline solids

Molecular solids, Ionic solids, and Atomic solids

Molecular solids

composite units are molecules

low melting point

ex. ice

Ionic solids

composite units are cations and anions

high melting points

ex. table salt, NaCl

Atomic solids

nonbonding, metallic, and network covalent

Nonbonding

held together by dispersion forces

low melting point

ex. solid xenon

Metallic

held together by metallic bonds

variable melting points

ex. gold

Network covalent

held together by covalent bonds

high melting points

ex. quartz

Solubility

the amount of solute that will dissolve in a given amount of solvent

Aqueous solutions have what as the solvent

water

Type of Solutions

Entropy

a measure of energy randomization or energy dispersal in a system

increases when the gases mix

spontaneous process

Intermolecular forces exist between

solvent-solute

solvent-solvent

solute-solute

Solvent-solute interactions > solvent-solvent and solute-solute then

solution genrally forms

Solvent-solute interactions = solvent-solvent and solute-solute then

Solution generally forms

Solvent-solute interactions < solvent-solvent and solute-solute then

Solution may or may not form, depending on relative disparity

Common Polar solvents

Water (H20), Acetone (CH3COCH3), Methanol (CH3OH), and Ethanol (CH3CH2OH)

Common Nonpolar solvents

Hexane (C6H14), Diethyl ether (CH3CH2OCH2CH3), Toluene (C7H8), Carbon Tetrachloride (CCl4)

Miscible

when two liquids form a homogeneous solution in all proportions

Enthalpy of solution

overall enthalpy change of solution formation

Know this?

Heats of hydration

energy change that occurs when 1 mole of the gaseous solute ions are dissolved in water

exothermic for ionic compounds

Heats of Hydration…

Know this?

Saturated solution

has exactly the maximum amount of solute that can be dissolved in the solvent

Unsaturated solution

has less than the maximum amount of solute that can be dissolved in the solvent

Supersaturated solution

more than the maximum amount of solute that cen be dissolved in the solvent

Solubility decreases with

increasing temperature

Solubility increases with

increasing pressure

Henry’s Law

Molarity (M)

amount solute ( in mole)/ volume solution (in L)

mol/L

Morality (m)

amount solute (in mole)/ mass solvent (in kg)

mol/kg

Percent by mass

multiplications factor = 100 %

Mole fraction (x)

amount solute (in mol)/ total amount of solute and solvent (in mol)

Parts per million by mass (ppm)

multiplication factor = 10⁶

Parts per billion by mass (ppb)

multiplication factor = 10⁹

If given molarity (M),

assume 1 L solution

If given molality (m)

assume 1 kg solvent