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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
