Isotope Formulae,
Electron
Configurations &
Orbital Diagrams
Isotope Formulae
•  Provide element’s symbol
•  Mass number
– mass# = #p+ + #n
– written as a superscript to the left
•  Atomic number
– atomic# = #p+ or #e– written as a subscript to the left
Isotope Formulae
Mass#
X
Atomic#
Carbon has two naturally occurring isotopes:
carbon-12 and carbon-13
12
C
6
13
C
6
Isotope Formulae
Give the isotope formula for each of the
following:
1. Hydrogen with 2 neutrons
2. Fluorine with 9 neutrons
3. Uranium with 143 neutrons
3
H
1
18
F
9
235
U
92
Valence Electron(s)
•  The electron(s) farthest from
the nucleus or in the outermost
energy level.
Aufbau Principle
•  Comes from German word
meaning “to build”
•  Electrons will occupy lower
energy orbitals first
Pauli Exclusion
Principle
•  An atomic orbital can hold at
most two electrons.
•  If an atomic orbital holds two
electrons, they must have
opposite spins.
Hund’s Rule
•  When filling atomic orbitals of
equal energy, place electrons
with parallel spins in the
orbitals first. Then, place the
oppositely spinning electrons
in to the orbitals.
Electron Configurations
•  Also describe where electrons
live within an atom
•  It’s like a translation of
quantum numbers.
•  They give the energy level,
atomic orbital, and number of
electrons residing in the
orbital and energy level.
Electron Configurations
•  Energy level
– May be any positive integer
– Just like the principal quantum
number
Electron Configurations
•  Atomic Orbital or Sublevel
– Represented by letters: s, p, d, f
– Translates azimuthal number
and magnetic number
– s is the same as l = 0
– p is the same as l = 1
– d is the same as l = 2
– f is the same as l = 3
Electron Configurations
•  Number of Electrons
– in either an atomic orbital or a
sublevel
– max of 2 in the s sublevel
– max of 6 in the p sublevel
– max of 10 in the d sublevel
– max of 14 in the f sublevel
Electron Configurations
•  Use the periodic table to guide
you in writing electron
configurations.
•  Find the link between 2,6,10,
and 14 and the periodic table.
Electron Configurations
•  Hydrogen
energy
level
1
1s
sublevel/
orbital
# of
electrons
Electron Configurations
•  Write the e- configurations of the
next 9 elements (through Ne).
He…1s2
Look
at
the
sum
2
1
Li… 1s 2s
of the superscripts…
2
2
Be… 1s 2s
B… 1s22s22p1
Electron Configurations
C…
2
2
3
N… 1s 2s 2p
O… 1s22s22p4
F… 1s22s22p5
2
2
2
1s 2s 2p
Ne…1s22s22p6
Electron Configurations
•  Shorthand configurations are
written by assuming that you can
let the symbol of the noble gas
preceding the valence electrons
represent the e- configuration to
that point.
Electron Configurations
…shorthand
2
He…1s
Li…
Be… [He]2s2
2
1
B… [He]2s 2p
2
2
C… [He]2s 2p
1
[He]2s
Electron Configurations
…shorthand
N…
O… [He] 2s22p4
F… [He] 2s22p5
2
3
[He]2s 2p
Ne…[He] 2s22p6
Electron Configurations
…shorthand
1
Na… [Ne]3s
Si… [Ne] 3s23p2
Cl… [Ne] 3s23p5
Ar… [Ne] 3s23p6
Electron Configurations
…shorthand
2
Ca…[Ar]4s
Sc… [Ar] 4s23d1
Mn…[Ar] 4s23d5
Se… [Ar] 4s23d104p4
Electron Configurations
…shorthand
I…
La… [Xe] 6s25d1
Ce…[Xe] 6s25d14f1
2
10
5
[Kr] 5s 4d 5p
Hg…[Xe] 6s24f145d10
Exceptional Electron
Configurations…shorthand
2
4
Cr… [Ar] 4s 3d
1
5
[Ar] 4s 3d
Cu…[Ar] 4s23d9 [Ar] 4s13d10
Mo…[Kr] 5s24d4 [Kr] 5s14d5
Ag…[Kr] 5s24d9 [Kr] 5s14d10
Orbital Diagrams
•  Show the electron configuration
while illustrating the Aufbau
Principle, Pauli Exclusion
Principle, and Hund’s Rule
•  Place energy on the y-axis
•  Use lines to represent orbitals
•  Use up and down arrows to
indicate spin
Orbital Diagrams (template)
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for H
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for He
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for Be
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for C
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for O
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Orbital Diagram for P
3px
3py
3pz
2py
2pz
3s
E
2px
2s
1s
Wrap-Up
•  Write the electron configuration
for nitrogen.
•  Write the orbital diagram for
nitrogen.