ELECTRONIC STRUCTURE and PERIODIC LAW
In 19th century scientist tried to classify elements
known at that time. German Julius Lothar Meyer
and Russian Dimitri Ivanovich Mendeleev
independently classified elements according
to the PERIODIC LAW:
ELEMENTS with similar chemical
properties occur at regular (periodic)
intervals when the elements are arranged
in order of increasing atomic numbers.
The arrangement of elements in a
table based on Periodic Law is called
PERIODIC TABLE.
Dimitri Ivanovich Mendeleev
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
GROUPS
PERIODS
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
British scientist Ernest Rutherford proposed
a solar system model for atoms in which
negative electrons moved in circular orbitals
around the positive nucleus.
In 1913 Niels Bohr proposed model of a
hydrogen atom where the single electron could
occupy orbits only at specific distances from
Nitrogen Atom, 14 7N
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nucleus. The addition of energy
would move electrons to higher
(fixed) orbit, whereas electrons
would release energy to move
to a lower orbit
(closer to the nucleus).
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
In 1926 Austrian physicist Erwin Shrödinger (received Nobel Prize in
physics in 1933) proposed QUANTUM MECHANICAL MODEL
where precise paths of electrons cannot be determined accurately,
but only the probability if their location.
The three simplest orbitals
of the hydrogen atom are
depicted on the left in
pseudo-3D, in cross-section,
and as plots of probability (of
finding the electron) as a
function of distance from the
nucleus. The average radius
of the electron probability is
shown by the blue circles or
plots in the two columns on
the right. These radii
correspond exactly to those
predicted by the Bohr model.
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
The location and energy of electrons around a nucleus can be specified
Using three terms: SHELL, SUBSHELL and ORBITAL.
SHELL : a location and energy of electrons around a nucleus that
is designated by a value for n, where n = 1, 2, 3, etc.
SUBSHELL : a component of a SHELL that is designated
by a letter from the group s, p, d and f.
ORBITAL : a volume of space around atomic nuclei in which
electrons of the same energy move.
Groups of orbitals with the same n value
form subshells.
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
Orbital
Symmetry
Node geometry
Spherical
nodes/shell*
Orbitals/set
s
spherical
spherical
n
1
p
cylindrical
around x, y, or z
axis
1 planar - perpendicular to
axis of orbital; remainder
spherical
n-1
3
d
complex
2 planar surfaces diagonal
to Cartesian axis; remainder
spherical
n-2
5
f
complex
complex
n-3
7
* n = the shell, with n = 1 the ground state or lowest possible energy shell. Thus n may have
integral values from 1 - infinity.
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ELECTRONIC STRUCTURE and PERIODIC LAW
single s orbital
in every shell
3 p orbitals
of the same
size and shape
(along X, Y,
or Z axes)
Every orbital
can contain
0, 1 or 2 electrons.
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5 different d orbitals
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
4fx(3x2-y2)
4fx(x2-3y2)
4fyz2
4fxz2
4fxyz
4fz(x2-y2)
4fz3
7 f orbitals - for your aesthetic pleasure!
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
s 12 orbital
electrons
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p
3 orbitals
6 electrons
Chemistry 21A
d
5 orbitals
10 electrons
f
7 orbitals
14 electrons
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
Number of
electrons in the
outermost
occupied
(valence) shell
is the same as
the group
number.
The maximum
number of
electrons in the
valence shell
is 8 and every
period ends with
an element
having 8
electrons in the
valence shell.
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
ELECTRONIC CONFIGURATIONS
Orbitals fill "from the
bottom up" and they
occupy separate
orbitals (spin
unpaired) before
pairing up. The
latter effect is
known as Hund's
rule, and it is a
consequence of the
smaller degree of
repulsion between
electrons when they
can occupy
separate orbitals
which have different
orientations in
space.
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
ELECTRONIC CONFIGURATIONS
The up- and down-arrows represent the
two possible orientations of the
magnetic moment of the electron
(misleadingly known as electron "spin").
Only electrons with opposite magnetic
moments (opposite “spins”) can occupy
the same orbital (Pauli exclusion
principle). It explains why orbitals can
contain only two electrons.
Hund’s rule and Pauli exclusion
principle can be combined: Electrons
will pair with other electrons in an orbital
only if there is no
The placement of the dots around the
empty orbital of the
symbol of the element is a schematic
same energy
representation of electrons in the
available and if there
valence shell, which determine
is one electron with
chemical behaviour of elements.
opposite spin already
They are called Lewis formulas.
Gilbert Newton Lewis in the orbital.
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
ELECTRONIC CONFIGURATIONS
ELECTRONIC
CONFIGURATIONS
H 1s
O 1s2 2s2 2p4
Ne 1s2 2s2 2p6
Mg 1s2 2s2 2p6 3s2 or abbreviated form Mg [Ne]3s2
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
Symbol
Be
Mg
Ca
Sr
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full form
1s2
1s2
1s2
1s2
Chemistry 21A
2s2
2s2 2p6 3s2
2s2 2p6 3s2 3p6 4s2
2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
abbr. form
[He]2s2
[Ne]3s2
[Ar]3s2
[Kr]3s2
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
The last and the highest energy electron found in an element is called
THE DISTINGUISHING ELECTRON.
THE DISTINGUISHING ELECTRON
determines the chemical properties of an element.
If the distinguishing electron is in
an d subshell it is called
TRANSITION
ELEMENT
If the distinguishing electron is in an s or p subshell it is called
REPRESENTATIVE ELEMENT
If the distinguishing electron is in
an f subshell it is called
INNER-TRANSITION
ELEMENT
El Camino College
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
Metals
Located to the
left of the
heavy line
Shiny, ductile
Good
conductors of
heat and
electricity
Metalloids
Have properties somewhat between
those of metals and nonmetals.
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Nonmetals
Located to the right of the heavy line
Dull and brittle, poor conductors,
good insulators
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ELECTRONIC STRUCTURE and PERIODIC LAW
Cl
chlorine
N
Br
I
bromine
iodine
P
Bi
nitrogen
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phosphorus
arsenic
bismuth
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
The atoms sizes are in
picometers (pm = 10-12 m).
Two factors must be taken into
consideration in explaining this periodic
trend
(1) Increasing nuclear charge
(2) Increasing shell
Along a period (left to right) the atomic
number increases while the valence
electrons remain in the same shell. Thus,
due to the increasing nuclear charge
(pulling electrons closer to the nucleus) the
radii of the atoms decrease left to right.
Top to bottom along a group the atomic
number continues to increase. However the
shell increases from shell 1 to shell 2 etc..
The atomic orbitals for each successive
shell get larger and larger - more than
compensating for the increased nuclear
charge. The result is atomic radii increase
top to bottom along a group.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
The ionization energy is the amount
of energy it takes to detach one electron
from a neutral atom.
The equation for the first ionization energy of sodium (I) is shown below:
Na --> Na+ + eThe equation for the second ionization energy (I2) is:
1
2
3
4
5
6
7
Na+ --> Na2+ + e-
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8
H
1312
He
2372
5250
Li
520
7297
11810
Be
899
1757
14845
21000
B
800
2426
3659
25020
32820
C
1086
2352
4619
6221
37820
47260
N
1402
2855
4576
7473
9442
53250
64340
O
1314
3388
5296
7467
10987
13320
71320
84070
F
1680
3375
6045
8408
11020
15160
17860
92010
Ne
2080
3963
6130
9361
12180
15240
Na
496
4563
6913
9541
13350
16600
20113
25666
Mg
737
1450
7731
10545
13627
17995
21700
25662
Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
2M + 2C2H5OH = 2C2H5OM + H2
2M + 2H2O = 2MOH + H2
2Rb + 2H2O = 2RbOH + H2
El Camino College
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Dr. Dragan Marinkovic
ELECTRONIC STRUCTURE and PERIODIC LAW
Abundances of the isotopes
ISOTOPES are atoms that
have the same atomic number
(number of protons) but
different mass numbers
(number of neutrons).
element
Z
symbo
l
A
abundanc
e
mass
excess
hydroge
n
1
H
1
99.9885
7.289
2
0.0151
13.136
3
0.000138
14.931
4
99.999863
2.425
6
7.59
14.086
7
92.41
14.908
helium
lithium
3
He
Li
beryllium
4
Be
9
100
11.348
boron
5
B
10
19.9
12.051
11
80.1
8.668
12
98.93
0
13
1.07
3.125
14
99.632
2.863
15
0.368
0.101
16
99.757
−4.737
17
0.038
−0.809
18
0.205
−0.782
carbon
Greek isos = "equal",
tópos = "site, place"
2
nitrogen
oxygen
6
7
8
C
N
O
The numerical difference between the actual measured mass of an isotope and A is called
either the mass excess or the mass defect (symbol Δ; see table).
El Camino College
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Dr. Dragan Marinkovic