1. ELECTRON CONFIGURATIONS

2. Early Models of the Atom
Rutherford
Small, massive, positively charged nucleus
nucleus surrounded by electrons
Niels Bohr
Showed electrons occupy orbitals
Orbitals have certain energy levels

3. Electrons Orbit the nucleus
At ground state they occupy lowest energy state
Electrons excited by heating
When cooled electron returns to original orbital releasing energy (light)

4. Energy Levels and Sub-levels
Electron configuration uses numbers and letters to describe position and energy level of electrons present.
Energy level identified by a number that relates to rows in the periodic table. 1, 2, 3 etc.
A letter represents a sub-level. s,p,d or f. First level has 1 sublevel (1s), second has 2 (2s, 2p) , third has three (3s, 3p, 3d).
Each sublevel has a number of orbitals which can hold two electrons. A superscript number identifies specific orbital. S has 1, P has 3, d has 5 and f has 7

5. Orbitals and the Periodic Table

6. Filling Orbitals
Electrons always fill orbitals with the lowest energy first.
1s<2s <2p<3s<3p<4s<3d
Copy Fig 5.2 From the Study guide

7. Orbital filling Diagram
Orbitals are filled so that as many electrons remain unpaired as possible.
High energy level
___
___
___
___
___
Example: Nitrogen 7 electrons 3d
___ 4s
___
___
___ 3p
___
1s2 2s2 2p3 ↑ ↑ ↑ 3s
___
___
___ ↑ ↓ 2p
___ 2s ↑ ↓
Low energy level
___ 1s

8. Energy levels and sub-levels
Main energy level
Sub-levels
Max. no. of electron pairs in sub-level
Max. no. of electrons in sub-level
Max. no. of electrons in main level 1 s 2 8 p 3 6 18 d 5 10 4 f 7

9. Example Lithium with 3 electrons 1s2 2s1 Potassium with 19 electrons
Iron with 26 electrons
1s2
2s2
2p6
3s2
3p6
4s1
1s2
2s2
2p6
3s2
3p6
3d6
4s2

10. Affect of Stability
Full and half filled orbitals have the most stable states.
This can result in a higher level orbital e.g. 3d being filled before a lower level orbital e.g. 4s
E.g. Copper
1s2 2s2 2p2 3s2 3p6 3d10 4s1

11. Ions
When ions are formed electrons are gained (anion) or lost (cation) to form a stable arrangement.
E.g.
P3-, S2-, Cl- & Ar are all
1s2 2s2 2p2 3s2 3p6
They are Isoelectronic

12. Ion Formation Electrons are lost from highest energy levels first.
That means 4s electrons are lost BEFORE 3d electrons

13. Write electron configuration for each of the following atoms:
Practice
Write electron configuration for each of the following atoms:
C Ca
S Ni
Ti Zn
V Cr
Br Cu

14. Give the electron configuration of each of the following ions
Cu Br Mn Ca Ga3+
Complete the following table
Element or ion
Atomic number
No of protons
Mass number
No of neutrons
Charge
Electron configuration 11 23
Fe3+ 30 3+ 16 34
1S2 2S2 2P6 3S2 3P6 28
[Ar] 3d3