1.
2- Electronic Configuration
Objectives:
• Describe the electronic configuration of the atom
i. Define the term 'electron configuration'
ii. Write the electron configurations for the elements of the periodic table
iii. Demonstrate how electron orbitals are filled in accordance with Aufbau
Principle, Pauli's Exclusion Principle and Hund's Rule
1 of 49 © Boardworks Ltd 2005
Activity 1: Draw the electronic arrangement of 12Mg, 6C, and 22Ti
Think- Pair and Share
2 of 49 © Boardworks Ltd 2005
Electronic Configuration: Energy Levels -Shells
How Are Electrons Arranged?
• Electrons are not evenly spread.
• The exist in layers known as shells.
• The arrangement of electrons in these shells is
often called the electron configuration.
1st Shell=K
2nd Shell=L
3rd Shell=M
4th Shell=N
How Many Electrons per Shell?
• Each shell has a maximum number of electrons
that it can hold= 2n2.
The maximum
K:n=1 can hold 2 electrons
L: n=2 can hold 8 electrons
M:n=3 can hold 18 electrons
Which Shells Do Electrons go into?
• Opposites attract.
• Protons are + and electrons are – charged.
• Electrons will occupy the shells nearest the
nucleus unless these shells are already full.
1st Shell: Fill this first
2nd Shell: Fill this next
3rd Shell: And so on
Energy Levels
Bohr’s Model of the Atom (1913)
1.The total energy of the atom is (quantized) ≡ only take certain values ≡ energy
levels of an atom
2.Light is emitted as e- moves from one energy level to a lower energy level
3.The minimum energy state (n=1) is the ground state of the hydrogen atom ≡
corresponding level is called K level
n is called the principal quantum number) = 1,2,3,…
Energy Levels
1.When an atom receives energy from an external source, the
electron moves to a higher energy level (n>1) ≡ atom is
excited
2. The Energy Diagram of the Hydrogen atom is used to
represent its different energy levels. The energy diagram is
obtained from the following relation
En = - (13.6/n2 ) ev
n (principal quantum number) = 1,2,3,…
Bohr’s Model of the Atom (1913)
3.The successive energy levels that appear in the energy
diagram are not evenly spaced distinctly spaced for small
value of n become closer for increasing values of n
nearly superimposed when n is very large
Subshells
Each shell is made up of one or more subshells
All electrons in a subshell have the same energy
Designated s, p, d, f ..
Sublevel energy: s<p<d<f
Timberlake LecturePLUS 2000
SUBSHELL/Sublevels
• The number of subshells located in a shell is
the same as the number of the shell.
e.g. n=1 has one subshell: s
n=2 has 2 subshells: s and p
n=3 has 3 subshells: s, p, and d
n=4 has 4 subshells: s, p, d and f
• The number of the shell to which a subshell
belongs is combined with the letter of the
subshell to clearly identify subshells.
• E.g: n=1 subshell is 1s
n=2 subshells are 2s and 2p
n=3 subshells: 3s, 3p, and 3d
n=4 subshells: 4s, 4p, 4d and 4f
Electrons Allowed
All electrons in the same sublevel have the same energy.
There is a limit to the number of electrons that can fill a
subshell.
s sublevel 2 electrons
p sublevel 6 electrons
d sublevel 10 electrons
f sublevel 14 electrons
Timberlake LecturePLUS 2000
Electron Configuration
List of subshells containing electrons
Written in order of increasing energy
Superscripts give the number of electrons
Example: Electron configuration of neon
number of electrons
1s2 2s2 2p6
main shell subshell
Timberlake LecturePLUS 2000
SUBSHELL FILLING ORDER (not in order)
• The electron configuration of an atom is the
distribution of electrons in the different energy
sublevels.
• Electrons will fill subshells in the order of
increasing energy of the subshells.
• To write the electron configuration of an atom we
fill the energy sublevels successively with electrons
according to Klechkowski’s rule
Electron Configurations
Element Configuration Element Configuration
H Z=1 1s1 He Z=2 1s2
Li Z=3 1s22s1 Be Z=4 1s22s2
B Z=5 1s22s22p1 C Z=6 1s22s22p2
N Z=7 1s22s22p3 O Z=8 1s22s22p4
F Z=9 Ne Z=10 1s22s22p6
1s22s22p5
(2p is now full)
Na Z=11 1s22s22p63s1 Cl Z=17 1s22s22p63s23p5
K Z=19 Sc Z=21 1s22s22p63s23p64s23d1
1s22s22p63s23p64s1
Fe Z=26 1s22s22p63s23p64s23d6 Br Z=35 1s22s22p63s23p64s23d104p5
Note that all the numbers in the electron configuration add up to the atomic
number for that element. Ex: for Ne (Z=10), 2+2+6 = 10
Activity 2:
Time 5 minutes
• Draw the electronic configuration of :
Person 1:27Co:
Person 2: 32Ge :
Person 3: 38Sr:
Person 4: 25Mn
• Form groups 1, 2, 3 and 4 and discuss the answer (2 min)
Learning Check: Quiz (6 min)
H.W.: Moodle: w311-electron-configuration-worksheet
