Chemistry 101
Prof. Hammon
CH. 8 – PERIODIC PROP. OF THE ELEMENTS
Electron Configuration – tells us where the electrons are
located for specific elements.
Rules for Writing Electronic Configurations:
1. Fill lowest energy orbitals first. (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p,
5s, 4d, 5p, 6s) (Aufbau Principle)
1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
6d
2. Only 2 electrons per orbital (Pauli exclusion principle).
Opposite spins
Spin Quantum number (ms):
Values for ms are +½ (arrow up) or – ½ (arrow down)
Helium Orbital diagram
1s
(He: 2 electrons)
4f
5f
Chemistry 101
Prof. Hammon
He electron config.:
1s2
(e- represented by superscript)
Quantum #s for 2 electrons in Helium:
n
1
1
l
0
0
ml
0
0
ms
+½
-½
3. Don’t pair electrons in equal energy orbitals until you have to
(Hund’s Rule).
Nitrogen: 7 electrons
N Orbital diagram
1s
2s 2px 2py 2pz
N electron config.: 1s22s22p3
Example: Write orbital diagram & electron configuration for:
Element # of e-
e- config.
Orbital diagram
K
Write the set of 4 quant #s that represent the last e- added to K
n
l
ml
ms
Chemistry 101
Prof. Hammon
Noble Gas Shorthand Electron Configurations (Inner Electron
Configuration):
K
Write electron configurations for:
F
F-
K+
Chemistry 101
Prof. Hammon
For transition metal ion remove ns electrons before (n-1)d
electrons.
Fe
Fe2+
Zn
Zn2+
Paramagnetic: Atom contains unpaired electrons. Attracted to
a magnetic field.
Diamagnetic: Atom contains paired electrons only. Not
attracted to a magnetic field.
Is iron paramagnetic or diamagnetic?
Is zinc paramagnetic or diamagnetic?
Chemistry 101
Prof. Hammon
Valence Electrons – electrons in the outer most shell (the one
with the highest principle quantum #)
Core Electrons – electrons not in the outermost shell
i.e.
Phosphorus (P) electron configuration
1s22s22p63s23p3
Core e-
valence e-
Determine the valence and core electrons for calcium.
Determine the valence and core electrons for gallium (Ga).
Exception: Transition Metals with d orbitals that are not
completely filled. The electrons in the outermost d orbitals are
counted as valence e-.
Determine the valence and core electrons for titanium (Ti).
Chemistry 101
Prof. Hammon
Electron Configurations & the Periodic Table
 Elements in a family (column) have the same # of valence
electrons. Column # corresponds to # of valence electrons.
 Row # corresponds to highest shell (principle quantum #).
The highest quantum # increases by 1 as move down column.
 Columns 1A & 2A have s block outer shell electron config.
 Columns 3A-8A have p block outer shell electron config.
 Transition metals have d block electron config.
 Lanthanides & Actinides have f block electron config.
To write Electron Configurations from the periodic table:
1) Write core electron configuration as proceeding noble gas in
brackets.
2) Write valence electrons by assigning highest principal
quantum # as row # & determine # of e- in s, p, d or f blocks.
3) For elements containing d electrons, the principle quantum #
is equal to the row # minus 1.
4) For elements containing f electrons, the principle quantum #
is equal to the row # minus 2.
Chemistry 101
Prof. Hammon
Write the electron configuration for selenium using the periodic
table.
Write the electron configuration for titanium using the periodic
table.
Write the electron configuration for europium (Eu) using the
periodic table.
Chemistry 101
Prof. Hammon
THE OCTECT RULE
 Atoms and ions are most stable when they have a complete
outer shell of eight electrons.
(Noble-Gas wanna-be’s)
i.e.
Na 1s22s22p63s1 (outer shell has ___e-)
Na+ +
Na
Na+
i.e.
e-
1s22s22p6 (outer shell has ___ e-)
[Ne]
O
1s22s22p4 (outer shell has ___ e-)
O
+
O2-
2e-
O2-
1s22s22p6 (outer shell has ___ e-)
[Ne]
Octet Rule (some reasons why it is not a perfect rule):
1. Hydrogen can only acquire 2 electrons.
2. The octet rule can’t be applied to transition elements
because they are too far removed from a noble gas
structure.
Chemistry 101
Prof. Hammon
Goodyear Blimp vs. the Hindenburg
•
•
Hindenburg
Hydrogen – Reactive and Flammable
Goodyear Blimp
Helium – Inert (non-reactive) and Inflammable
Periodic Law:
When elements are arranged in order of increasing atomic
number, certain sets of properties recur periodically.
Example: Hydrogen behaves like Li and Na & Helium behaves
like Ne and Ar (inert gases).
Why is hydrogen more reactive than helium?
Chemical properties are mostly determined by valence electrons.
 Atoms with 8 valence electrons are stable.
 Alkali metals are reactive with one valence electron (if lose
electron will have noble gas electron configuration).
Why are halogens reactive?
Chemistry 101
Prof. Hammon
PERIODIC TRENDS
Atomic Size: how far the outermost electrons are from the
nucleus determines the size of the atom.
 Atomic size increases as you move down a family of the
periodic table.
 Atomic size decreases as you move right across a period of
the periodic table.
Is Ca or Ba larger?
Effective Nuclear Charge increases as you move across a row of
the periodic table resulting in decrease of atomic size.
Z effective (effective nuclear charge): the amount of positive
charge an outermost electron experiences.
Slater’s Rule
Z = nuclear charge of atom (#of protons)
S = Shielding: the amount of positive charge blocked by other
electrons.
Chemistry 101
Prof. Hammon
Shielding (S):
Actual percent of shielding experienced by outermost electron is
dependent on # of e- & location of other electrons.
Principle Quantum #
same n
n-1
n-2 (or lower)
Shielding
35%
85%
100%
S=[# of e- in same n ___ x (0.35)] + [# of e- in n-1__ x (0.85)] + [# of e- in n-2(or <)__ x (1.00)]
Calculate Zeff for Aluminum
Al electron config.:
S = [# of e- in same n ___ x (0.35)] + [# of e- in n-1___ x (0.85)] + [# of e- in n-2 ___ x (1.00)]
S = _____
Z= ____
Zeff = Z – S
Chemistry 101
Prof. Hammon
Calculate Zeff for Silicon
Si electron config.:
S=
Z= ____
Zeff = Z – S
Calculate Zeff for Phosphorous
P electron config.:
Ion Size
Cations are always smaller than the atoms they come from.
Anions are always larger than the atoms they come from.
Chemistry 101
Prof. Hammon
PERIODIC TRENDS
Ionization Energy (I.E.): energy required to remove an electron
from an atom in the gaseous state.
1st Ionization Energy: energy required to remove 1st electron.
2nd Ionization Energy: energy required to remove 2nd electron.
 Ionization energy increases as you move to the right across a
row (period) of the periodic table. (Zeff increases so harder to
remove electrons)
 Ionization energy decreases as you move down a column
(family) of the periodic table. (electrons farther from nucleus
are easier to remove)
Does Mg or Cl have a higher ionization energy?
I.E. Exception: I.E. for oxygen (1300 kJ/mol) is less than
nitrogen (1400 kJ/mol).
 It is easier to remove an electron from oxygen than nitrogen
due to electron-electron repulsion.
Chemistry 101
Prof. Hammon
Electron Affinity (E.A.): energy associated with gaining an
electron by an atom in the gaseous state.
 Electron Affinities become more negative as you move to the
right across a row of the periodic table. (adding an electron
becomes more exothermic)
 Electron Affinities become more negative as you move up
group 1A metals. (adding an electron becomes more
exothermic)
Does Li or K have a more negative electron affinity?
E.A. Exception: Fluorine in halogen trend for E.A.
 E.A. is less negative for F (-328 kJ/mol) than Cl (-349
kJ/mol), because electrons are entering a smaller more
densely packed F atom that leads to electron–electron
repulsion.