- On moving from left to right in a period, the number of valence electrons in elements increases from 1-8.
III period elements:
|
At.no.
|
11
|
12
|
13
|
14
|
15
|
16
|
17
|
18
|
|
Symbol
|
Na
|
Mg
|
Al
|
Si
|
P
|
S
|
Cl
|
Ar
|
|
e-.Confgn
|
2,8,1
|
2,8,2,
|
2,8,3
|
2,8,4
|
2,8,5
|
2,8,6
|
2,8,7
|
2,8,8
|
|
Valenc.e-
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
The first element in every period has 1
electron and the last element in every period has 8 valence
electrons(Except He in the first period). - The valency of elements increases from 1 to 4 and then decreases to 0
|
III elements
|
Na
|
Mg
|
Al
|
Si
|
P
|
S
|
Cl
|
Ar
|
|
Valency
|
1
|
2
|
3
|
4
|
3
|
2
|
1
|
0
|
The valency of an element: The no. of
electrons lost or gained (or shared) by one atom of an element to
achieve the nearest electron configuration, gives us the valency of
the element. Thats why, S has 2 valency, instead of
6 and Cl has 1 instead of 7.
-
On moving from left to right in a
period, the size of the atoms decreases, due to large positive charge
on the nucleus , the electrons are pulled in more close to the
nucleus and the size of the atom decreases. -
On moving from left to right in a
period, the metallic character of elements decreases and non metallic
character increases. This is because the tendency of atoms to lose
electrons decreases and to gain electrons increases. - On moving from left to right in a
period, the chemical reactivity first decreases and then increases.
- On moving from left to right in a
period, the basic nature of oxides decreases and acidic nature of increases.
|
