The document discusses electron configurations, which describe the arrangement of electrons in an atom's orbitals. It notes that electrons occupy specific orbitals and that orbitals are grouped into shells. It then provides examples of the full and abbreviated electron configurations for the first 20 elements, showing how many electrons occupy each orbital. The document also outlines the steps for writing abbreviated electron configurations using the noble gas of the same period.

1. Electron Configuration
An atom’s electron configuration is a shorthand
notation that shows the number and
arrangement of electrons in its orbitals.

2. Bohr-Rutherford diagram for sodium
Each circle is known as an orbit. They are numbered 1,2,3…..
There are obribitals located in each orbit.

3. Orbit Orbital Electron holding
capacity
1 s s=2
2 s,p p=6
3 s,p,d d=10
4 s,p,d,f f=14

5. Element
Electron configuration
1.Hydrogen 1s1
2.Helium 1s2
3.Lithium 1s2
2s1
4.Beryllium 1s2
2s2

6. 5.Boron 1s2
2s2
2p1
6.Carbon 1s2
2s2
2p2
7.Nitrogen 1s2
2s2
2p3
8.Oxygen 1s2
2s2
2p4

7. 9.Fluorine 1s2
2s2
2p5
10. Neon 1s2
2s2
2p6
11.Sodium 1s2
2s2
2p6
3s1
12.Magnesium 1s2
2s2
2p6
3s2
13.Aluminum 1s2
2s2
2p6
3s2
3p1

8. 14.Silicon 1s2
2s2
2p6
3s2
3p2
15.Phosphorous 1s2
2s2
2p6
3s2
3p3
16.Sulfur 1s2
2s2
2p6
3s2
3p4
17.Chlorine 1s2
2s2
2p6
3s2
3p5

9. 18.Argon 1s2
2s2
2p6
3s2
3p6
19.Potassium 1s2
2s2
2p6
3s2
3p6
4s1
20. Calcium 1s2
2s2
2p6
3s2
3p6
4s2

10. Abbreviated electron configuration
Follow these steps to write abbreviated electron
configurations.
Step 1:Find the symbol for the element on a
periodic table.
Step2: Find the symbol for the closest noble gas
the is located in one row above and put the
symbol in square bracket.
For example for iron the closest noble gas will be
[Ar]

11. Step3: Continue writing electron
configuration starting with the period
number of the element followed by s.
For iron abbreviated electron
configuration will be
[Ar]4s2
3d6
18 + 2+ 6= 26