CHEMISTRY FORM 44 CHEMISTRY 9

LESSON 5

How many square can fit inside the space?

?

How about this space?

?

According to Bohr’s Theory, the following theories were deduced.Electrons surrounding nucleus similar like

planetsurrounding sunElectrons are filled inside the orbitals called shells.Electrons filling in the shell from the lowest energy

level to the highest energy level (from the closet shell to the further shell)

Number of electrons occupied can be determined by using the formula 2n2

– 1st shell [2(1)2 = 2] – 2nd shell [2(2)2 = 8] – 3rd shell [2(3)2 = 18] – 4th shell [2(4)2 = 32]

So, let’s together draw and write the electron arrangement for the first 2oth elements

1

HHydrogen

1

Electron arrangement : 1

4

HeHelium

2

Electron arrangement : 2

7

LiLithium

3

Electron arrangement : 2 . 1

9

BeBeryllium

4

Electron arrangement : 2 . 2

11

BBoron

5

Electron arrangement : 2 . 3

12

CCarbon

6

Electron arrangement : 2 . 4

14

NNitrogen

7

Electron arrangement : 2 . 5

16

OOxygen

8

Electron arrangement : 2 . 6

19

FFluorine

9

Electron arrangement : 2 . 7

20

NeNeon

10

Electron arrangement : 2 . 8

23

NaSodium

11

Electron arrangement : 2 . 8 . 1

24

MgMagnesium

12

Electron arrangement : 2 . 8 . 2

27

AlAluminium

13

Electron arrangement : 2 . 8 . 3

28

SiSilicon

14

Electron arrangement : 2 . 8 . 4

31

PPhosphorous

15

Electron arrangement : 2 . 8 . 5

32

SSulphur

16

Electron arrangement : 2 . 8 . 6

35.5

ClChlorine

17

Electron arrangement : 2 . 8 . 7

40

ArArgon

18

Electron arrangement : 2 . 8 . 8

39

KPotassium

19

Electron arrangement : 2 . 8 . 8 . 1

40

CaCalcium

20

Electron arrangement : 2 . 8 . 8 . 2

RememberThe last number in each written electron

arrangement is named as valance electronFrom the number of valence electron, we can

conclude which group in the Periodic Table the element belongs to

Also, from the count of number, we can tell which Period in the Periodic Table does it belong to

Valance electron 1 2 3 4 5 6 7 8

Group 1 2 13 14 15 16 17 18

Count X 2 . X 2 . 8 . X 2 . 8 . 8 . X

Period 1 2 3 4