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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
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