Exam 1: Periodic Trends and Electrochemistry

Niels bohr propose that

electrons only occupy certain orbits of specific energy

The energy of electrons

quantized

Atoms and molecules have certain allowable

discrete energy levels

n

orbit or energy level

As n increases

distance from the nucleus increase and energy levels get closer in proximity

Emission

higher energy level to lower

Absorption

lower energy level to higher

Bohr model significance

electrons exist in energy levels and as electrons transition between levels, energy is exchanged

Limitation of Bohr model

only applicable for one electron systems and describes them in specific orbits (exact position)

De Broglie

a moving particle like electron also has wave-like properties

Heisenberg uncertainty principle

It is impossible to simultaneously know both the position and momentum of an electron and the more we know about one the less we know about another

Schrodinger equation incorporates

particle and wave behavior

Principal quantum number

n is referred to as an energy level or shell

n designates

size and energy

Angular momentum quantum number

l is referred to as subshell

l designates

the shape

l allowed values

from 0 to n-1

s

0

p

1

d

2

f

3

magnetic quantum number

m(l) and refers to the orbital

m(l) designates

the orientation in space

m(l) allowed values

-l to l

Magnetic spin quantum number

m(s) describes the spin of an electron within an orbital

m(s) values

-1/2 or 1/2

Node

a point in which the probability of finding electron density in an atom is zero

Node on a standing wave

where the amplitude is 0

Total number of nodes for an orbital

n-1

planar node

aka angular, dictated by orbital shape and equal to l

radial

spherical, dictated by l and n and equal to n-l-1

Crossing the x-axis in a wave function

indicates change in phase and presence of node

radial probability distribution function

the number of times curve touches x-axis is the number of radial nodes (origin does not count)

Subshells within the same shell

degenerate or of the same energy

electrostatic interactions

energy levels are split in system with less than an electron

energy increases as

n and l increase

an orbital’s shape significantly

impacts its penetrating ability and the distribution of electron density.

angular nodes reduce an electron’s

access to nucleus and influence its energy levels.

the degree of penetration is significant for

s-orbital, but is attenuated for p and d orbitals

penetration of electrons into the inner shell reduces

the magnitude of the shielding they experience and increases their ability to shield to shield other electron

z

nuclear charge and number of protons in the nucleus that influences the energy levels of electrons.

Zeff

the actual magnitude of the positive charge that is “experienced” by an electron in an atom

Z vs Zeff

electrons are simultaneously attracted to nucleus, but repelled one another

Shielding

partial obstruction of nuclear charge by other electron

Zeff formula

Z- sigma

sigma

number of core electrons

Core electrons are most effective at shielding

valence electrons

Electrons in a lower shell of the same subshell type

are very effective at shielding (1s is good at shielding 3s)

electrons in the same shell but different subshell type are

less effective at shielding one another but lower energy subshells can provide some shielding to higher energy electrons

electrons within the same subshell

do not shield one another

Aufbau principle

place electrons in lowest energy orbitals first

Pauli exclusion principle

no two electrons can have the same four quantum numbers

Hund’s rule

the most stable arrangement of electrons in degenerate orbitals is the one in which parallel spins are maximized

Cr exception

4s1 3d5 instead of 4s2 3d4

Copper exception

4s1 3d1

Mo exception

5s1 4d5

Ag exception

5s1 4d10

Au

6s1 5d10

periods

rows

groups (families)

column

Electron configurations for s and p block cations

remove electron from the highest energy valence orbital

electron configurations for anions

add electron to the lowest energy available orbital

electron configuration for d block cations

remove electron from the highest n orbital

electron configuration for d block anions

lowest available orbitals first

In the ground state the ns subshell is lower in energy

than the (n-1)d subshell

As the number of core electron remains constant

the number of valence electrons and Zeff increases

Zeff trends

increase from left to right and top to bottom

n trends

decreases from left to right, increases from top to bottom

The lanthanide contraction

the poor shielding properties of the f orbitals do not compensate for the increasing nuclear charge; therefore the 5d valence electrons experience a higher than predicted Zeff

Cation radius

smaller than parent atom

Cation characteristics

decrease electron repulsions, sometimes reduction in n, increase in p:e ratio

Anion radius

larger than parent

Anion characteristics

increased electron repulsions, decreased p:e

Isoelectronic series

members have the same number of electrons but different nuclear charges

Charges in isoelectronic series

as nuclear charges increase, ions become smaller

Ionization energy

the minimum energy required to remove an electron from an atom (or ion) in the gas phase

IE trends

increase from left to right, decreases top to bottom

large positive values with IE

difficult to remove electrons

small positive values with IE

easier to remove electrons

At some point it becomes nearly impossible to remove another electron

which means the noble gas electron configuration has been attained

As Z increase, the system becomes more stabilized

due to lower orbital energies and orbitals contract (max electron probability moves closer to the nucleus)

Electron affinity

the energy released when gaseous atom/ion accepts an electron

Energy in EA is negative

when adding an electron is easy and favorable

E in Ea is positive

when adding an electron is difficult

EA trends

increase from left to right and decreases from top to bottom

EA anomalies

Li, Be, C,N, noble gases

Electronegativity

the ability for an atom to draw shared electron density towards itself in a chemical bond

EN trends

increases from left to right and decrease top to bottom

most EN elements

F, O, N, Cl, Br, I, C, S, H

oxidation number of F

-1

oxidation state of oxygen

-2 unless with itself and or a higher element

hydrogen

+1, -1 with metal

group 1A ox state

+1

Group 7a ox state

-1

group 2a ox state

+2

Redox reaction

a chemical reaction in which electrons are transferred from one reactant to another

Redox reactions must be balanced

mass and charge

Oxidation

loss of electron leads to more positive ox state

Reduction

gain of electron leads to more negative ox state

reducing agent

the species that donates electron to reduce another species; becomes oxidized