General Chemistry

Faculty of Allied Medical Sciences

(MGGC-101)&(GRGC-101)

Supervision:Prof.Dr.Shehata El-Sewedy

Dr.Fatma Ahmed

Electron Configuration and

periodicity

Outcomes By the end of this lecture, the

students will be able to1-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 :

1S1denotes the principle quantum number n

denotes the numer of electrons in the orbital or subshell

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 one1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f4s<3d in energy so 4s filled firstYou 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 > half filled > partially filled orbital orbital orbital

More stable 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 ↓↓.

1 S2gives the number of electrons in the orbital electrons in S orbital= 2

gives the principle quantum no. (n)

1 so n=1 i.e k2 so n=2 i.e L3 so n=3 i.e M gives the Angular

quantum no. (l)

where l=0 i.e S orbital, m=0 l=1 i.e P orbital m=+1,0,-1 l=2 i.e d orbital m=+2,+1,0,-1,-2

He4

2

Ex:

(N=2) 1S2

For first electron n=1, l=0, m=0, S= + 12

For second electron n=1, l=0, m=0, S= - 12

5-Valence shell electrons (outer most shell)It’s the electrons in the last shell in the atom

He4

21S2 v.s.e

C6

12 1S2 v.s.e2S2 2P2

f irst shell

second shell

Ex

6-Electronic configuration according to nobel gases (inert gases)

2He 1S2

10Ne 1S2 2S2 2P6

18Ar 1S2 2S2 2P6 3S2 3P6

36Kr 1S2 2S2 2P6 3S2 3P6 4S2 3d10 4P6

ExWrite 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 filled29Cu 18[Ar] 4S1 3d10

24Cr 1S2 2S2 2P6 3S2 3P6 4S2 3d4 Less stable xxxxx

24Cr 1S2 2S2 2P6 3S2 3P6 4S1 3d5 more stable √√√√√

half filled >> partially filled24Cr 18[Ar] 4S1 3d5

Write the electronic configuration of O+, O, O-, O-2 & what are the valence shell electrons of O?Answer

8O

2S2 2P4

v.s.e

1S2

8O+ = O-e- = 8-1= 7 e-s O+ 1S2 2S2 2P3

8O- = O+e- = 8+1= 9 e-s O- 1S2 2S2 2P5

O-2 1S2 2S2 2P6

v.s.e of oxygen 8O are 6 e-s

Quiz time

Write the electronic configuration of 29Cu and 24Cr comment in your answer?

Student Question

Define and give exampleValence shell electrons

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?

Hund’s rule states

AssignmentsGroup A and B

Moemen Mohamad El-saidAbeer SalahFarida Maher

Homogenous mixture in industrial world

Ahmad Rada Kamel – Ahmad Mohamad Abd El Salam- Ahmad El Said- Ahmad Alaa

Molecular Formula

Sara Lotfy- Shimaa Saied – Esraa Sameh-Ahmad Shadra-Ibrahim El-Habet- Ibrahim El Said

Elemental analysis

Mohamad Ramadan - Mohamad Nabil- Mahmoud Hamdi- Abd El Rahman Abd El-Moneim –Yossef Gamal- Mohamad Shabaan -

Physical properties in Chemistry

RECOMMENDED TEXTBOOKS:

1-Raymond Chang. Chemistry. 10th ed. 20092-Zumdehl. International edition. 2009