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 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 m s = +1/2 and down for m s = -1/2. Example So the orbital diagram for Hydrogen (Z=1) is as follows:

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 :

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 P 3 orbital 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 ↓↓.

Ex : (N=2) 1S 2 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 29 Cu and 24 Cr comment in your answer? Answer 29 Cu (At.no.= 29) 29 Cu 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3d 9 Less stable xxxxx So One electron from 4S 2 migrates to 3d 9 to be completely filled 3d 10 which is more stable Then 29 Cu 1S 2 2S 2 2P 6 3S 2 3P 6 4S 1 3d 10 more stable √√√√√ Completely filled >> partially filled 29 Cu 18 [Ar] 4S 1 3d 10

24 Cr 1S 2 2S 2 2P 6 3S 2 3P 6 4S 2 3d 4 Less stable xxxxx 24 Cr 1S 2 2S 2 2P 6 3S 2 3P 6 4S 1 3d 5 more stable √√√√√ half filled >> partially filled 24 Cr 18 [Ar] 4S 1 3d 5

Write the electronic configuration of O +, O, O -, O -2 & what are the valence shell electrons of O? Answer 8 O 8 O + = O-e - = 8-1= 7 e - s O + 1S 2 2S 2 2P 3 8 O - = O+e - = 8+1= 9 e - s O - 1S 2 2S 2 2P 5 O -2 1S 2 2S 2 2P 6 v.s.e of oxygen 8 O are 6 e - s

Quiz time

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

Student Question

Define and give example Valence shell electrons Write the electronic configuration of 29 Cu and 24 Cr 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

Assignments Group A and B Moemen Mohamad El-said Abeer Salah Farida 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

R ECOMMENDED TEXTBOOKS : 1-Raymond Chang. Chemistry. 10th ed Zumdehl. International edition. 2009