Writing Electron Configurations
Electron Configurations of Atoms
in their Ground State
The electron configuration is a listing of the sublevels in order
of filling with the number of electrons in that sublevel
written as a superscript.
Kr = 36 electrons = 1s22s22p63s23p64s23d104p6
primary
energy
levels
sublevels
Electron Configurations of Atoms
in their Ground State
The electron configuration is a listing of the sublevels in order of filling
with the number of electrons in that sublevel written as a superscript.
Kr = 36 electrons = 1s22s22p63s23p64s23d104p6
A short-hand way of writing an electron configuration:
Rb = 37 electrons = 1s22s22p63s23p64s23d104p65s1 = [Kr]5s1
Order of Sublevel Filling
in Ground State Electron Configurations
Start by drawing a diagram
putting each energy shell on
a row and listing the sublevels,
(s, p, d, f), for that shell in
order of energy (left-to-right
Next, draw arrows through
the diagonals, looping back
to the next diagonal
each time
1
H
1s1
3
Li
1s22s1
2
He
1s2
4
Be
1s22s2
5
6
7
8
9
10
B
C
N
O
F
Ne
1s22s22p1 1s22s22p2 1s22s22p3 1s22s22p4 1s22s22p5 1s22s22p6
H: 1s1
He: 1s2
Li: 1s22s1
Be: 1s22s2
1s
2s
2p
3
Li
1s22s1
4
Be
1s22s2
5
6
7
8
9
10
B
C
N
O
F
Ne
1s22s22p1 1s22s22p2 1s22s22p3 1s22s22p4 1s22s22p5 1s22s22p6
B: 1s22s22p1
C: 1s22s22p2
N: 1s22s22p3
O: 1s22s22p4
F: 1s22s22p5
Ne: 1s22s22p6
1s
2s
2p
Practice — write the full ground state orbital diagram
and electron configuration of potassium.
K Z = 19, therefore 19 e−
Based on the order of sublevel filling, we will need the first six sublevels
↿⇃
↿⇃ ↿⇃ ↿⇃ ↿⇃
↿⇃ ↿⇃ ↿⇃ ↿⇃
↿
1s
2s
3s
4s
s sublevel holds 2 e−
p sublevel holds 6 e−
d sublevel holds 10 e−
f sublevel holds 14 e−
2p
3p
Therefore the electron configuration is
1s22s22p63s23p64s1
Electron Configuration & the Periodic Table
Example: Write the full ground state orbital diagram
and electron configuration of manganese
Mn
Z = 25, therefore 25 e−
Based on the order of sublevel filling, we will need the first seven sublevels
↿⇃
↿⇃ ↿⇃ ↿⇃ ↿⇃
↿⇃ ↿⇃ ↿⇃ ↿⇃
↿⇃
1s
2s
3s
4s
s sublevel holds 2 e−
p sublevel holds 6 e−
d sublevel holds 10 e−
f sublevel holds 14 e−
2p
3p
↿ ↿ ↿ ↿ ↿
3d
Therefore the electron configuration is
1s22s22p63s23p64s23d5
Electron Configuration & the Periodic Table
The Group number corresponds to the number of
“valence electrons” for representative elements.
The length of each “block” is the maximum number of
electrons the sublevel can hold.
The Period number corresponds to the principal
energy level of the valence electrons.
What does the following electron
configuration mean?
1s22s22p63s23p64s23d104p2
1s22s22p63s23p64s23d104p2
1s22s22p63s23p64s23d104p2
1s22s22p63s23p64s23d104p2
Ge
32e
Valence Electrons
Electrons residing in the
HIGHEST PRINCIPAL ENERGY LEVEL
Core and Valence Electrons
Core and Valence Electrons
Na
Cl
Be: 1s22s2
Si: 1s22s22p63s23p2
O: 1s22s22p4
Cl: 1s22s22p63s23p5
Shapes of Atomic Orbitals
d orbitals
f orbitals
Why are Atoms Spherical?
Periodic Trends
Atomic Radii
Ionization Energy
Metallic Character
Shielding
In a multi-electron system, electrons are simultaneously
attracted to the nucleus and repelled by each other.
Outer electrons are shielded from nucleus
by the core electrons.
The shielding causes the outer electrons to not experience
the full strength of the nuclear charge and they are not
held as tightly (or “as close”) to the nucleus.
Periodic Trends: Atomic Size is Influenced by Two Factors
#1: As you move to the right across a period in the
periodic table, atomic size decreases.
#2: As you move down a column in the periodic
table, atomic size increases.
Trend in Atomic Radius – Main Group
Periodic Trends: Atomic Size is Influenced by Two Factors
#1: As you move to the right across a period in the
periodic table, atomic size decreases.
The atomic size of an atom is determined by the distance
between the outermost electrons and the nucleus.
The size of an orbital depends on the principal quantum number.
With each step across a period, the number of protons in the
nucleus is increasing.
This increase in the number of protons results in a greater pull on
the electrons from the nucleus, causing atomic size to
decrease.
Periodic Trends: Atomic Size Has Two Factors
#2: As you move down a column in the periodic
table, atomic size increases.
As you move down a column in the periodic table, the highest
principal quantum number, n, increases.
Since the size of an orbital increases with increasing principal
quantum number, the electrons that occupy the outermost
orbitals are farther from the nucleus as you move down a
column.
Periodic Trends in Atomic Radius
Trend in Atomic Radius
Practice – Choose the atom in each pair with the larger radius
N or F
C or Ge
N or Al
Al or Ge
C or O
Li or K
C or Al
Se or I
Ionization Energy
the energy required to remove an
electron from an atom
General Trends in 1st Ionization Energy
The larger the effective nuclear charge on the electron,
the more energy it takes to remove it.
The farther the most probable distance the electron is
from the nucleus, the less energy it takes to remove it.
1st IE decreases down the group.
1st IE generally increases across the period
Valence electrons are easier to remove than core electrons.
General Trends in 1st Ionization Energy
Choose the atom in each pair with the
larger first ionization energy
Al or S
As or Sb
N or Si
O or Cl
Mg or P
Ag or Cu
Ca or Rb
P or Se
Metallic Character
Metallic character is how closely an element’s
properties match the ideal properties of a metal.
Metals tend to lose electrons in their chemical
reactions, while nonmetals tend to gain
electrons.
As you move across a period in the periodic table,
ionization energy increases, which means that
electrons are less likely to be lost in chemical reactions.
Metallic character decreases as you move to the
right across a period and increases as you
move down a column in the periodic table.
Choose the more metallic element in each pair
Sn or Te
P or Sb
Ge or In
S or Br
Mg or Al
Si or Sn
Br or Te
Se or I