Faculty of Allied Medical Sciences
General
Chemistry
(MGGC-101)&
(GRGC-101)
Electron
Configuration and
periodicity
Supervision:
Prof.Dr.Shehata El-Sewedy
Dr.Fatma Ahmed
Outcomes
By the end of this lecture, the
students will be able to
1-Understand the electron configuration
2-learn to rules used to build the electron
configuration in many-electron atoms
3- To know valence shell electrons
4-Recognize Pauli exclusion principle
An “electron configuration” of an atom is a
particular distribution of electrons among
available subshells.
Orbital diagram: a diagram used to show how
the orbitals of a subshell are occupied by electrons.
Each orbital is represented by a box and each
group of orbitals is labeled by its subshell notation.
Electrons are represented by arrows:
up for ms = +1/2 and down for ms = -1/2.
Example
So the orbital diagram for Hydrogen (Z=1) is as follows:
1S
It is convenient to have a shorthand notation
for representing the electron configuration.
This is done by writing the symbol of each
orbital occupied by an electron with a
superscript to indicate the number of electrons
occupying that orbital. Thus, for hydrogen, the
electron configuration is :
denotes the numer of electrons
in the orbital or subshell
denotes the principle
quantum number n
1
1S
denotes the angular
quantum number l
Rules used to build the electron configuration in many-electron
atoms
Three rules govern the arrangement of electrons in atoms:
1-The Aufbau Principle - (means building-up in
German):
Electrons are added to sublevels of lower energy then to the
higher one
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s,
5f
4s<3d in energy so 4s filled first
You need not memorize this order. As you will see, it can be
easily obtained:
Order for Filling Atomic Subshells
2-Hund’s rule states degenerated orbitals (orbitals of same
energy) are filled singly with electrons first (unpaired) with
parallel spin rather than pairing to avoid repulsion between
electrons
Ex P3 orbital
Un stable
Un stable
Stable
3-Order of stability
Completely filled
orbital
> half filled
orbital
More stable
> partially filled
orbital
less stable
4-Pauli exclusion principle states that no two electrons in the same
atom have the same values of all four quantum no.∴ an orbital will have
maximum of 2 electrons.
↑ unpaired electron
↑↓ paired electrons and not ↑↑ or ↓↓.
Ex
(N=2)
1S2
For first electron n=1, l=0, m=0, S= +
For second electron n=1, l=0, m=0, S= -
5-Valence shell electrons (outer most shell)
It’s the electrons in the last shell in the atom
Ex:
6-Electronic configuration according to nobel gases (inert gases)
Ex
Write the electronic configuration of 29Cu and 24Cr comment in your answer?
Answer
29Cu
(At.no.= 29)
29Cu
1S2 2S2 2P6 3S2 3P6
4S2 3d9
Less stable
xxxxx
So
One electron from 4S2 migrates to 3d9 to be completely filled 3d10 which is more
stable
Then
29Cu
1S2 2S2 2P6 3S2 3P6 4S1 3d10
more stable
Completely filled >> partially filled
1
10
29Cu 18[Ar] 4S 3d
√√√√√
24Cr
1S2 2S2 2P6 3S2 3P6 4S2 3d4
24Cr
1S2 2S2 2P6 3S2 3P6 4S1 3d5
half filled >> partially filled
1
5
24Cr 18[Ar] 4S 3d
Less stable
more stable
xxxxx
√√√√√
Write the electronic configuration of O+, O, O-, O-2 & what are the valence shell electrons of O?
Answer
8O
= O-e- = 8-1= 7 e-s
8O = O+e = 8+1= 9 e s
O-2
v.s.e of oxygen 8O are 6 e-s
8O
+
O+ 1S2 2S2 2P3
O- 1S2 2S2 2P5
1S2 2S2 2P6
Quiz time
Write the electronic configuration of 29Cu
and 24Cr comment in your answer?
Student Question
Define and give example
Valence shell electrons
Hund’s rule states
Write the electronic configuration of 29Cu and 24Cr
comment in your answer?
Write the electronic configuration of O+, O, O-, O-2 & what are
the valence shell electrons of O?
Assignments
Group A and B
Homogenous mixture in
industrial world
Moemen Mohamad El-said
Abeer Salah
Farida Maher
Molecular Formula
Ahmad Rada Kamel –
Ahmad Mohamad Abd El SalamAhmad El Said- Ahmad Alaa
Elemental analysis
Sara Lotfy- Shimaa Saied – Esraa
Sameh-Ahmad Shadra-Ibrahim ElHabet- Ibrahim El Said
Physical properties in Chemistry
Mohamad Ramadan - Mohamad
Nabil- Mahmoud Hamdi- Abd El
Rahman Abd El-Moneim –Yossef
Gamal- Mohamad Shabaan-
RECOMMENDED TEXTBOOKS:
1-Raymond Chang. Chemistry. 10th ed.
2009
2-Zumdehl. International edition. 2009