Chem 209 Lecture 1
Chem 209 Lecture 1
Chem 209 Lecture 1
Atomic Structure
Prof. Jet G. Guerrero, R.Ch, M.Sc.
Inorganic Chemistry
If organic chemistry is considered to be the
chemistry of carbon, then inorganic chemistry
is the chemistry of all elements except carbon.
Inorganic chemistry is not simply the study of
elements and compounds; it is also the study of
physical principles.
The Nuclide
atomic number, Z
number of protons in the nucleus
mass number, A
number of protons and neutrons in the nucleus
A Z = # of neutrons
Isotopes
Nuclides of the same element
Same number of protons and electrons; but
Different number of neutrons
Different mass numbers.
e.g.
Allotropes
Allotropy is the property of some chemical
elements to exist in two or more
different molecular forms.
e.g.
diamond, graphite, and buckminsterfullerene (C 60)
S6, S8, and polycatenasulfur (Sx)
Drill #1: Ar
1. Calculate the value of Ar for naturally occurring
Cu if the distribution of isotopes is 69.2% 63Cu
and 30.8% 65Cu; accurate masses are 62.93 and
64.93.
2. What is the ratio of 63Cu:65Cu?
Drill #1: Ar
63Cu:65Cu is 2.25:1.
Mass Spectroscopy
Capable of separating and detecting individual
ions even those that only differ by a single
atomic mass unit.
Molecules containing different isotopes and has
difference in molecular form can be
distinguished.
Mass Spectroscopy
Separates isotopes
MS plots A/e not AR or atomic weight
Separates allotropes
MS plots M/e not MR or average molar mass
intensity/wavelength/temperature
relationship
where ,
Plancks constant, h = 6.626 x 10-34 J.s
= frequency ( in Hz or s-1)
c = 2.998 x 10 10 cm/s
= wavelength
Lyman series, n = 1
Balmer series, n = 2
Paschen, Brackett and Pfund series, n = 3, 4 and
5 respectively.
24
Name
Values
Principal
1, 2, 3,
Role
from R(r)
Angular
Momentum
0, 1, 2, ,
(n-1)
from
A (, )
Describes angular
dependence and
contributes to the energy
(shape)
ml
Magnetic
0,1, 2,
from
A (, )
Describes orientation in
space (direction)
ms
Spin
(1/2)
where
A(, )
A2(, )
Determines the shape of an atomic orbital.
It is ALWAYS POSITIVE.
Signs (+ or -) were assigned for lobes for
convenience.
Important in orbital interactions during bonding.
A2(, )
A2(, )
Contour Plots
contour lines indicate lines along which the
function is constant
1s:
Contour Plots:
2pz
2 lobes.
The probability to find the electron at a certain position is highest
in these lobes.
2 colors = 2 different signs. Changes in the sign of a wave function
are very important, because they are related to the energy of the
wave function
Contour Plots:
3dxy
4 lobes.
Opposite lobes have the same sign, neighboring lobes
have opposite sign.
The isosurfaces on which a wave function is zero, are
called nodal planes . In general the energy increases
when the number of nodal planes increases.
There are two nodal planes. One is the xz- and the
other the yz-plane.
The upper and lower lobe resemble the lobes of a p function, except both lobes
have the same sign. The middle lobe is a torus with an opposite sign to that of
the upper and lower lobe. The nodal planes for 3dz2 are two cones.
Spin-orbit coupling
L = Orbital angular momentum =
with 2l +1 possible vector directions
S = Spin angular momentum =
J = Total angular momentum =
with 2j+1 possible vector orientations
J is inner quantum number with values l+s and
l-s.
Shielding Effect
An electron in a 2s or 2p atomic orbital experiences the
effective charge, Zeff, of a nucleus partly shielded by the
1s electrons.
2p orbital penetrates the 1s orbital less than a 2s orbital
does
2p electron is shielded more than a 2s electron.
occupation of the 2s atomic orbital gives a lower energy
system
E(2s) < E(2p).
E(3s)< E(3p) < E(3d)
E(4s) < E(4p) < E(4d) < E(4f)
Exchange Energy, e
- Arises from purely quantum mechanical consideration
- Depends on the number of possible exchanges between two
electrons with the same energy and spin.
- Negative in energy.
Drill!!
for p5
Drill!!
for p5
One configuration only.
- Example: Scandium
Multielectron System
Two effects are considered:
Electron-electron repulsion
Spin-pairing energy
Spin-pairing energy
refers to the energy associated with paired electrons sharing one
orbital and it's affect on the molecules surrounding it.
Two types:
Paramagnetic and diamagnetic
e-e repulsion
Results from the coulomb repulsion (c) of like
charges
For transition metal valence electrons (VE),
e-e repulsion >>>>>>> spin-pairing energy
72
a 4s electron
and
a 3d electron is:
Hence,
Ionization Energy
1st IE is internal energy change, E, or potential
energy change, U at Zero K
E(g) -> E+(g) + e
2nd IE E+(g) -> E2(g) + e is also the 1st IE of ion E+
E(g) -> E2+(g) + 2e
Ionization Energy
IE = IE = IE1 + IE2
It is BEST used for H like atoms because e-e
repulsion and e pairing reduces IE and the
Energy, E, becomes no longer n dependent.
Slaters Rules
Electrons in groups higher than e considered
contributes NOTHING to S
For ns or np e considered
Other e in same group contribute 0.35 each
Each e in n-1 grpcontribute 0.85
Each e in n-2 group contribute 1.0
For nd or nf e considered
Other e in same group contribute 0.35 each
All other e below the group contribute 1.0 ea
1s22s22p63s23p63d1
Zeff = Z S
Zeff = Z S
= 19 [8(0.85) + 10 (1.00)
= 2.20
Based on Z* alone, MORE STABLE.
= 18 (1.00)
= 1.00
Ionization Energy
Z* or Zeff = Z S
S is screening or shielding constant
Ionization Energy
Drill!!
Which electron will ionize first in Mn (Z=25),
4s2 or 3d5?
Drill!!
Which electron will ionize first in Mn (Z=25),
4s2 or 3d5?
ANSWER: 4s2
Drill!!
What is the 1st, 2nd, and 3rd ionization energy of
Ca (Z=20)?
Electronegativity
Mulliken: M = (IE + EA)/2
Paulings relative scale sets 4.0 to F, which relates to bond enthalpies.
For atoms A and B,
96.5 kJ/mol (PA PB)2 = B(A-B) + (1/2)[B(A-A)+B(B-B)]
P= 1.35 M1/2 - 1.37
Allred and Rochow
-Relates to Z*/r2
Drill!!
For 1s2 2s2 2p6 3s2 3p6 4s2
Find: 1st IE, EA, electronegativity.
Drill!!
For 1s2 2s2 2p6 3s2 3p6 4s2
Find: 1st IE, EA, electronegativity.
1st IE = (13.6(2.85)2/16) = 6.9eV
EA = 6.044
Estimates off due to e-e repulsions and E not
only dependent on n in multielectron cases.
Drill!!
For 1s2 2s2 2p6 3s2 3p6 4s2
Find: 1st IE, EA, electronegativity.
Atomic Radius
Van der Waals radius
- the radius of an imaginary hard sphere which can
be used to model the atom for many purposes.
Covalent radius
- Dependent on valency and coordination number
Ionic radius
- Dependent on oxidation state
Polarizability,
Ability to distort a neighboring field.
High polarizability or softness if separation of frontier
orbitals is small.
Low polarizability or hardness, , if separation of frontier
orbitals is high.
Polarizability increases rapidly with an increase in atomic
size
Due to dispersion forces
Polarizability
Hard-Soft distinction
Reactions are more favorable for hard-hard and
soft-soft interactions
Polarizability
Hard acids and bases
Relatively small, compact and nonpolarizable
d electrons are NOT available for bonding
Hard acids are cations with large + charges (3+ or larger)
Soft acids
Larger and more massive the atom, the softer it is
Due to shielding
d electrons are readily available for bonding (+1
cations)
Polarizability
Soft-soft: HOMO and LUMO energies are much
closer
Hard-hard: stronger, depends on a larger range
of electrostatic force
Absolute hardness, = 1/2 (I-A)
where I = IE and A = EA, both in eV.
Softness , = -1
Spectral Terms:
total spin angular momentum (S)
(2S+1) is the multiplicity of the
S is the total spin quantum number.
2S+1
corresponds to a
singlet
doublet
triplet
quartet
Spectral Terms:
total orbital angular momentum (L)
L
corresponds to a
Spectral Terms:
total angular momentum (J)
J = L+S, , |L-S|
where S = total spin angular momentum
L = total orbital angular momentum
Based on LS or Russell-Saunders coupling
RussellSaunders Coupling
also known as the spin-orbit coupling and LS
coupling
in light atoms (generally Z < 30), electron
spins si interact among themselves so they combine to
form a total spin angular momentum S.
The same happens with orbital angular momenta li,
forming a total orbital angular momentum L.
S and L are to be added together and form a total
angular momentum J.
Spectral Term Symbol
LJ
2S+1
Drill!!
Determine the ground spectral term for:
1. Fluorine (Z=9)
2. Beryllium (Z=4)
3. Lithium (Z=3)
Drill!
Determine the ground spectral term for:
1. Fluorine (Z=9) 2P3/2 or 2P1/2
2. Beryllium (Z=4) 1S0
3. Lithium (Z=3) 2S1/2
Spectral Terms
Consider C (Z=6): 1s22s22p2
Using the same methods,
L = 0, 1, 2 (S, P, D)
S = 0 (if spin-paired) or 1 (parallel spin)
2S+1 = 1 or 3, respectively.
It may seem that J = L+S, , |LS| = 0, 1, 2, 3.
But no. Because then there will be 2 electrons with
n=2, l=1, ml =1, , ms =+1/2. This CANNOT be.
violates Paulis principle.
Drill!!
How many microstates do the following have:
1. d2
2. p6
3. f5
Drill!!
How many microstates do the following have:
1. d2 = 45
2. p6 =1
3. f5 =2002
127
and
ms
1
-1
-1
-2
ms
1
ml
-1
-1
ms
1
-1
-1
-1
-2
1 =1
s =-20, 2s+1
L = 2; L+SL-S = 2
1D2
ms
1
ml
-1
-1
ml
ms
1
-11
-1
-1
-1
-2
-1
ms
-1
1 =1
s =-20, 2s+1
s = 0,-22S+10= 1
L = 2; L+SL-S = 2 L = 0 1S0
1D2
ms
1
-1
-1
-2
ms
1
-1
-1
-2
s = 1, 2s+1 = 3
L=1P
L-S..L+S = 0,1,2
3
P0, 3P1, 3P2
Drill!!!
Try to use the array method for the excited state
of Li: 1s1 2s1 2p1
Draw the rest of the possible configurations.
e.x.
Drill!!!
Excited Li
1s1 2s1 2p1
Drill!!!
Drills.
Find the spectral terms for:
1. d2
2. f2
3. f3
4. d3 and d7
142
d2
143
f2
144
f3
Drills.
Find the spectral terms for:
1. d2
2. f2
3. f3
2
4. d3 and d7
H 2G 4F 2D 2P 4S
Photoelectron Spectroscopy
In a PES experiment, an atom or molecule is irradiated
with electromagnetic radiation of energy E, causing
electrons to be ejected from the system.
Each electron possesses a characteristic binding energy
and must absorb an amount of energy equal to, or in
excess of, this binding energy if it is to be ejected.
The energy of an ejected electron is that in excess of the
binding energy assuming that E is greater than the
binding energy.
Excess energy of electron = E (binding energy of
electron)
Photoelectron Spectroscopy
Since the excess energy can be measured and E is
known, the binding energy can be determined.
Koopmans theorem relates the binding energy of
the electron to the energy of the atomic or
molecular orbital in which it resides.
This relationship allows photoelectron
spectroscopy to be used to estimate the energies
of occupied orbitals, and, thus, obtain
information about the ordering of orbitals in a
particular atomic or molecular species.
149
We write: 2J+1= 15 (1 + 3 + 5 + 5 + 1)
E(C)average = (1/15)(E(3P0)) + (3/15)(E(3P1)) +
(5/15)(E(3P2)) +
(5/15)(E(1D2)) + (1/15)(E(1S0))
VOIE = IE - Eave
152
Radioactivity
A nuclide is radioactive if it decomposes to form
a different nuclide.
Types of emission:
-particle
Basically, an electron.
Energy: (0.03-5) x 10-13 J
-particle
Energy: (6-16) x 10-13 J
Its emission lowers the atomic number by two
and the mass number by four.
Example:
-radiation
same range as -particle, but has greater
penetrating power
Very short wavelength very high energy
Energy: 1 mol 3.6 x 108kj/96.35 eV/kj= ca. in MeV
Nuclear Transformations
Neutrino
Near zero mass; uncharged
Accompany the emission from the nucleus of a positron
Antineutrino
Near zero mass; uncharged
Accompany the emission from the nucleus of an electron
Variable energy
161
Nuclear Properties of
Elements
Drills!
Write the nuclear reactions.
1. Carbon-14 undergoes decay
2. Technietium-99m undergoes isomeric
transition, producing a gamma emission.
3. Carbon-11 decays by positron emission.
4. Radon-222 undergoes decay to form Polonium218.
5. Rubidium-81 undergoes decay by electron
capture.
Drills!
Write the nuclear reactions.
1. Carbon-14 undergoes decay
2. Technietium-99m undergoes isomeric
transition, producing a gamma emission.
3. Carbon-11 decays by positron emission.
4. Radon-222 undergoes decay to form Polonium218.
5. Rubidium-81 undergoes decay by electron
capture.
166
Artificial Isotopes
Made by the bombarding the nuclei with highenergy neutrons or positively charged particles
The use of neutrons (uncharged)= more effective
No electrostatic repulsion by the nuclei.
Artificial Isotopes
Bombardment of nuclei with slow/thermal neutrons.
formed by fission of
and their kinetic energy is
reduced by elastic collisions with low atomic number
nuclei (e.g. ,
) during passage through graphite or
deuterium oxide (heavy water).
Energy: 0.05eV.
Example:
169
Nuclear Fission
Branching chain reaction
If this involves a quantity of
larger than a
171
Drill!!
Drill!!
Ans.
175
Use of Radio-isotopes
Nuclear Medicine
used in some forms of tomography
for diagnosis, treatment, and research
Agriculture
radiation is used to stop the sprouting of root crops after
harvesting, to kill parasites and pests, and to control the
ripening of stored fruit and vegetables
176
Use of Radio-isotopes
Food preservation
used to produce high-yield crops, disease and weather resistant
varieties of crops, to study how fertilizers and insecticides work, and
to improve the production and health of domestic animals
Mining Industry
examine welds, to detect leaks, to study the rate of wear, erosion and
corrosion of metals, and for on-stream analysis of a wide range of
minerals and fuels.
177
Heart
201Tl (, t1/2 = 73h, 78-80keV)
Thyroid
125I (, t1/2 = 13h, 159keV)
178