Valency

1
Valency (???)
2
Valency of different elements

• Valency (historical meaning) - no. of bonds to be
  formed by an atom.
• Historically, the values are deduced (??) from
  the formulas of some chemicals.e.g. H2O, CH4,
  HCl, NH3, H2, HF, H2S, PH3, SiH4, HBr, Cl2

3
Valency deduction exercise

• Deduce the valency of each kind of atom from the
  following formulas.H2O, CH4, HCl, NH3, H2, HF,
  H2S, PH3, SiH4, HBr, Cl2

4
Valency deduction exercise

• Deduce the valency of each kind of atom from the
  following formulas.H2O, CH4, HCl, NH3, H2, HF,
  H2S, PH3, SiH4, HBr, Cl2

5
Valency deduction exercise

• Deduce the valency of each kind of atom from the
  following formulas.H2O, CH4, HCl, NH3, H2, HF,
  H2S, PH3, SiH4, HBr, Cl2

6
Valency of some atoms
7
? Is there any connection (??) between the
position of an element in the periodic table and
the valency of the atom ?
8
Positions of the first 20 Elements
9
Positions of the first 20 Elements
10
? Is there any connection (??) between the
position of an element in the periodic table and
the valency of the atom ?
11
? Is there any connection (??) between the
position of an element in the periodic table and
the valency of the atom ?

• YesExcept H, the valency of an atom is the same
  as (8 group no.) of the atom. i.e. Extra no. of
  electrons required to fill the outermost shell.

12
Valency of different elements

• Valency - no. of bond to be formed

13
Real meaning of valency (???)
14
Real meaning of valency

• Valency of chlorine 1Formula of chlorine
  molecule Cl2

15
Covalent bond formation by electron sharing
co- means together jointly -valent means
outermost shell A non-metal atom can form bond by
sharing outermost shell electrons with another
atom.
16
Electrostatic nature of covalent bond
17
No. of electrons to be shared

• No. of electrons to be shared No. of electrons
  required to fill the outermost shell 8 - no.
  of electrons present 8 - group no.
• Exception H has only 1 electron to share.

18
No. of electrons to be shared

• No. of electrons to be shared by group VII atom
  e.g. F, Cl, Br, I 8 - 7 1
• No. of electrons to be shared by group VI atom
  e.g. O, S 8 - 6 2
• No. of electrons to be shared by group V atom
  e.g. N, P 8 - 5 3
• No. of electrons to be shared by group IV atom
  e.g. C, Si 8 - 4 4

19
No. of electrons to be shared

• Each electron to be shared can be considered as a
  hand to join with other atoms.
• For a stable molecule, all hands have to be held
  together i.e. all atoms have completely filled
  outermost shell.

20
Real meaning of valency

• Valency of an atom no. of bond to be formed
  no. of electrons to be shared 8 group no.