Chemistry 2 prelims

Solids

Fixed shape regardless of container

Particles’re closed together and held rigidly in place

Movement of solid particles - vibration, stretching, and rotation

Liquid

Adopts the shape of a container to the extent of its volume

Forms an upper surface

Particles're close together but are free to move around each other

Gases

Adopts container shape and fills it

Particles're far apart and move randomly

High kinetic energy

Compelling and predictable properties common to all

Gas Property 1

Gas volume changes significantly with pressure

• Solid and liquid volumes aren't greatly affected by pressure

• Pressure and volume are inversely proportional

Gas Property 2

Gases expand when heated (due to high energy) and shrink when cooled

• The volume change is 50 to 100 times greater for gases than for liquids and solids

Gas Property 3

Gases move freely / spread out and occupy all the space they can

Gas Property 4

Gases have relatively low densities

• Even in large containers, the amt of gas particles're relatively iow

Gas Property 5

Gases form a solution in any proportions

• They're freely miscible with each other

Kinetic Molecular Theory of Gases

Applies specifically to an ideal gas

5 postulates

Ideal gas

DNE

Imaginary gas whose behavior perfectly fits all assumptions of the KMT

Postulate 1

Gases consist of very large numbers of tiny spherical particles that’re far apart from each other compared to their size (lots of empty space)

Postulate 2

Gas particles are in constant rapid motion in random directions

Explains why gases move quickly

Postulate 3

Collisions between gas particles and container walls are elastic collisions

Elastic Collisions

Particles bounce off each other and don't lose energy when they collide

Colliding energy is conserved (remains the same)

Postulate 4

There are no forces of attraction or repulsion between gas particles

Postulate 5

The avg kinetic energy of gas particles is dependent upon the temp of the gas

Hotter = faster, cooler = slower: directly proportional

Pressure

Amt of force applied for each unit of area

Amt of force applied by the gas molecules against the walls of its container

P = f/a - force/area

Atmospheric pressure

Arises from the force exerted by atmospheric gases on the Earth's surface

Decreases with altitude (higher location = lower pressure)

Currently, the atmosphere is applying 14.7 lb/s² or 14.7 psi to the Earth's surface

Our body has 1 atm

1 atm is equal to

1.01325 × 10⁵ Pa

101.325 kPa

760 mmhg

760 torr

14.7 lb/s² or 14.7 psi

1.01325 Bar

Boyle's Law

P₁V₁ = P₂V₂

Pressure and volume are inversely proportional

Proposed by Robert Boyle in 1662

The volume of a gas at constant temp varies inversely with the pressure exerted on it

Less space (decreased volume) → more chances for gas and container wall collision → increased pressure

Charles' Law

V₁/T₁ = V₂/T₂

Proposed by Jacques Charles in 1780

The volume occupied by a fixed amt of gas is directly proportional to its absolute temp at constant pressure

Increased temp → increased KE → increase in space between gas particles → volume increase

The temperature should always be in Kelvin

Avogadro's Law

V₁/n₁ = V₂/n₂

Proposed by Amadeo Avogadro in 1880

The volume of a gas is directly proportional to the amt of gas at constant temp and pressure

Gases occupy all the space they occupy → volume increase → more gases need to occupy all available spaces

Avogadro's hypothesis

At a given pressure and temp, = volumes of all gases contain = number of moles/particles

At standard pressure and temp (STP, 0°C/273K and 1atm), the volume of 1 mole of any gas will occupy the same volume of 22.4L

1 mole = 22.4L (molar volume)

Ideal Gas Law

PV = nRT

For a specific amt of gas, the product of pressure and volume is directly proportional to the absolute temp

All gases have the same # of gas molecules when under equal volume, temp, and pressure

Universal Gas Constant (R)

Determined by using values at STP (273K, 22.4L, 1mol, 1atm)

PV/nT

= 0.08205 L*Atm / k*Mol

Diffusion

Gradual movement/mixing of diff gases by random molecular motion and collision in response to the diff concentration

Effusion

Gas escapes from a container through a hole of diameter considerably smaller than the free mean path of the molecules

Graham's Law of Effusion

The ratio of the rates of effusion for 2 gases is equal to the square root of the inverse ratio of the gases’ molar masses

Rate of effusion is inversely proportional to the square root of its molar mass

The time of effusion is directly proportional to the square root of its molar mass

relationship that closely approximates the rate of effusion

Light gases diffuse and effuse much more rapidly than heavier gases

Graham's Law of Effusion formulas

Tip: make gas A the lighter gas

Rate_A/Rate_B = √(M.M._B/M.M._A)

t_A/t_B = (M.M._A/M.M._B)

DALTON’S LAW OF PARTIAL PRESSURE

total pressure in a mixture is the sum of the partial pressures(exerted by an indiv gas) of the component gases.

higher partial pressure = more amt of gas molecules

partial pressure isn’t affected by types of gas (ex: 2molecs N + 2molecs O = 4molecs O2)

partial pressure is proportional to mole fraction

History of the Atomic Model

John Dalton

JJ Thomson (Plum Pudding Model)

Ernest Rutherford (Nuclear Model, Gold Foil Experiment)

Bohr Model - electron orbits, disproved due to Heisenberg’s Uncertainty Principle

Schrodinger (Quantum Mechanical Model Electron Cloud or Planetary Model) - orbitals; probable but uncertain positions of electrons

Quantum Mechanical Model

elements with only a few electrons still have many orbitals

Electron Configuration

shorthand way of determining the probable location of the electrons of an atom

nl^#

nl^#

n - energy lvl where the electrons are found

l - subshell where the electrons are found

# - # of electrons found in the energy lvl/subshell

atomic orbital

specified by 3 quantum #s

PRINCIPAL QUANTUM NUMBER (n)

Describes the size of the orbital

Indicates relative size of the orbital & relative distance of the electron from the nucleus.

symbolizes/corresponds to the atom’s energy level or shell occupied by the electron/atomic nucleus.

larger value = greater the distance from the nucleus and greater size of an atom

Integral value(+): 1, 2 , 3 ,4 , 5, 6, 7, ...

electron’s distance from the nucleus is directly proportional to the energy of the electron n is also a measure of the orbital

nearest energy lvl to the nucleus is K (followed by L,M,N)(?)

ANGULAR MOMENTUM QUANTUM NUMBER (l)

Describes the shape of the orbital

= to an integer from 0 to (n – 1)

indicates the sub energy levels of the atom and the relative shape and characteristics of the orbital

corresponds to the subshell or sublvl occupied by the electron

MAGNETIC QUANTUM NUMBER (m_l)

prescribes the three-dimensional orientation of the orbital in the space around the nucleus

value is -(l) to +(l), amt of possible m_l = number of orientations

indicates the spacial orientation of the orbital

MAGNETIC SPIN QUANTUM NUMBER (m_s)

Direction where the electron is spinning.

Determine if atom can produce a magnetic field

only possible values are +½ and -½ (because each orbital can only have at most one of each spin direction)

#

maximum number of electrons the l can hold