The document discusses electron configuration and the rules for filling electron orbitals in atoms. It explains that electrons exist in energy levels called shells, with each shell able to hold a maximum number of electrons according to the formula 2n2, where n is the shell number. Within shells, electrons occupy specific atomic orbitals that have distinct shapes and are grouped into sublevels. The document outlines Hund's rule and the Aufbau principle for determining the order in which orbitals are filled with electrons. Several examples of deducing full electron configurations for different elements are also provided.

1. Electron
configuration
D.M K.M S.H Z.M I.S

2. Contents
Introduction: Learning Objectives
Arrangement of electrons in an atom
2
Atomic orbitals
Electron configuration
Filling rules for electron orbitals
Energy levels and sublevels
Examples and questions

3. Introduction: Learning Objectives
1. Describe the structure of energy levels
2. Define s, p and d orbitals, and describe their
shapes
3. Describe the rules for assigning electrons to
subshells
4. Deduce the electron configuration of an atom
from its atomic number
5. Compare electron configurationsof atom and ion

4. Electrons exist in layers called shells (the shells can also be called energy or principal levels).
The number of shells is depends on the number of electrons.
Arrangement of electrons in an atom. Energy levels
Every shell has certain maximum number of electrons that can contain and it is calculated by
the following formula: 2n2, where n is the order of energy level
1st level holds a maximum of 2 electrons
2nd level holds a maximum of 8 electrons
3rd level holds a maximum of 18 electrons
This electron arrangement is written as 2, 8, 18.

5. What is the electron arrangement for 15P?
15P is a neutral atom with atomic number 15, subsequently it has 15 electrons.
Arrangement of electrons in an atom. Energy levels
15 electrons are distributed to shells starting from nearest to nucleus.
The 1st energy can hold maximum 2 electrons, the 2nd – 8 electrons.
5 electrons will be arranged in the 3rd shell & there are place for 13 more electrons.
3rd level holds 5 electrons out of 18 maximum
2nd level holds 8 electrons
1st level holds 2 electrons
This electron arrangement for 15P is written as 2, 8, 5.

6. Levels themselves divided into sublevels & sublevels consist of certain number of orbitals.
Sublevels are different from one another by number of orbitals and their shape.
Arrangement of electrons in an atom. Energy sublevels & orbitals
There are 4 types of sublevels: s, p, d and f.
Sublevel s p d f
Number of orbitals 1 3 5 7
Shape of orbitals
sphere dumbbell

7. Each orbital can hold TWO electrons.
Maximum Number of Electrons In Each Sublevel
Maximum Number
Sublevel Number of Orbitals of Electrons
s 1 2
p 3 6
d 5 10
f 7 14
Arrangement of electrons in an atom. Energy sublevels & orbitals
The shapes of orbitals show the places where electrons most probably can exist near nucleus.
Orbitals within the a sublevel are located in different directions.

8. 4f
4d
4p
4s
n = 4
3d
3p
3s
n = 3
2p
2s
n = 2
1s
n = 1
Energy
s
s
s
s
p
p
p
d
d f
Arrangement of electrons in an atom. Energy sublevels & orbitals
The 1st energy level has only s sublevel
The 2nd energy level has s and p sublevels
The 3rd energy level has s, p and d sublevels
The 4th energy level has s, p, d and f sublevels
Sublevels also differ from one another by energy.
Sometimes a sublevel of a lower shell might have higher
energy than the sublevels of higher shell. For example, 3d
sublevel of 3rd shell has higher energy than 4s sublevel of
4th shell.

9. • Hund’s Rule
• Within a sublevel, place one electron per orbital
before pairing them.
• “Empty Bus Seat Rule”
• Pauli Exclusion Principle
• Each orbital can hold TWO electrons with opposite spins.
WRONG RIGHT
RIGHT
WRONG
Filling rules for electron orbitals
• Aufbau Principle
• Electrons fill the lowest energy orbitals first.
• “Lazy Tenant Rule”
3d
5s
5p
6p
2s
3s
4s
5s
6s
7s
1s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
1s
2s
2p
3s
3p
4s
4p
4d
6s
7s
6d
4f
5f
5d
Energy

10. Filling rules for electron orbitals
Energy
levels
nucleus Upside-down house
1
2
3
4
5
6
7
s
p d
orbitals
sublevels (flats)
shells
electrons
Remember the row of filling of orbitals!
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 …

11. 1s
2s
3s
4s
5s
6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
1s 2s 2p 3s 3p 4s 3d 4p …
2 2 6 2 6 2 10 6
Electron configuration

12. How to deduce an electron configuration?
Remember the row of filling of orbitals!
Example 1:
Electronformula for 11Na:
Short electron formula: ...3s1
3 – shell; s – sublevel; 1 – number of е– on the outer shell (= number of valence е–)
Example 2:
Electronformula for 16S2-
First: e = Z – C = 16 – (–2) = 18
Then: 1s2, 2s2, 2p6, 3s2, 3p6
2 + 2 + 6 + 1 = 11
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 …
We need to know the number of electrons!
1s2, 2s2, 2p6, 3s1
Z = 11
; e = 11 (because the charge is 0)
*EXCEPTIONS!
24Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
29Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10

13. ➢ As - Arsenic ( Z=33, e=33):
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
Examples and questions
➢ Cu - Copper( Z=29, e=29)
1s2 2s2 2p6 3s2 3p6 4s1 3d10
➢ Cr - Chromium( Z=24 , e=24)
1s2 2s2 2p6 3s2 3p6 4s1 3d5
1s2 2s2 2p6 3s2 3p6 3d6 not 1s2 2s2 2p6 3s2 3p6 4s2 3d4
➢ S - Sulfur ( Z=16, e=16):
1s2 2s2 2p6 3s2 3p4
➢ F - Fluorine ( Z=9, e=9):
1s2 2s2 2p5

14. Thank You!