structure of molecule

1. CHEMISTRY
TOPIC : STRUCTURE OF MOLECULES.

2. WHAT IS CHEMICAL BOND?
 Chemical bond is defined as a
force of attraction between
atoms that holds them together
in a substance.
 Why do atoms form chemical
bond?
 Atoms achieve stability by
attaining nearest noble gas
configuration i.e. ns2, np6 .
 2 or 8 electrons in the valence
shell of an atom is sign of
stability for atoms.

3. WHAT IS OCTET AND DUPLET RULE ?
 Octet rule
 Attaining of 8 electrons in the valence shell of an
atom is called octet rule.
 Duplet rule
 Attaining of two electrons in the valence shell of an
atom is called duplet rule.
 Elements like hydrogen and helium follow duplet
rule.

4. HOW DO ATOMS FOLLOW OCTET RULE?
 An atom can accommodate 8 electrons in its
valence shell in three ways.
 By giving valence shell electrons (if they are less
than three) to other atom.
 By gaining valence shell electron (if the valence
shell has 5 or more than 5 electrons)
 By sharing valence shell electrons.

5. TYPES OF CHEMICAL BOND
 Chemical bonds are of four types:
 Ionic bond
 Covalent bond
 Dative or coordinate covalent bond
 Metallic bond

6. BONDING AND NON BONDING ELECTRONS
 Bonding electrons:
 The valence electrons which are involve in
chemical bonding are termed as bonding electrons.
 Non bonding electron:
 The electrons that belongs to valence shell of an
atom but do not involve in boding is called non
bonding electrons.
 7N= 1s2, 2s2,2p3

7. IONIC BOND
 The type of chemical bond,
which is formed due to
complete transfer of electron
from one atom to another atom
is called ionic bond
 The elements of group 1 and 2
have tendency to lose electron
while group 15 to 17 have
tendency to gain electron.

8. EXAMPLE OF IONIC BOND
 11Na=1s2,2s2,2p6, 3s1
 17Cl=1s2,2s2,2p6, 3s2,3p5
 𝑁𝑎 → 𝑁𝑎+ + 1e- (1s2,2s2,2p6=Ne)
 𝐶𝑙 + 1𝑒
−
→ 𝐶𝑙
−
(1s2,2s2,2p6,3s2,3p6=Ar)
 Na+ + Cl- → NaCl

9. PROPERTIES OF IONIC COMPOUNDS
 Ionic compounds are solid in nature because they
are made up of positive and negative charges .
Theses charges held together with strong
electrostatic force of attraction.
 They have high melting and boiling point
 They are good conductor of heat and electricity in
molten or solution form
 They are mostly crystalline solid
 They are easily soluble in water.

10. COVALENT BOND
 The type of bond, which is
formed due to mutual sharing
of electrons is called covalent
bond.
 Covalent bond form between
atoms of group 13 to group 17.

11. FORMATION OF COVALENT BOND

12. TYPES OF COVALENT BOND
 Depending upon number of bond pair covalent
bond divided in to three types.
 Single covalent bond
 Double covalent bond
 Triple covalent bond

13. SINGLE COVALENT BOND
 When one electron is contributed by each bonded atom
is called single covalent bond.
 Single covalent bond is indicated by a line (-) between
bonded atoms.
 For example HCl, Cl2, CH4

14. DOUBLE COVALENT BOND
 When each bonded atom contributes two electrons, two
bond pair are shared and a double covalent bonds
formed
 The bond pairs are indicated as double line (=) between
atoms
 For example O2, C2H4

15. TRIPLE COVALENT BOND
 When each bonded atom contributes three electrons, three
bond pair are shared and a triple covalent bond formed.
 The bond pairs are indicated as three line (≡) between
atoms.
 For example N2 and C2H2.

16. PROPERTIES OF COVALENT COMPOUNDS
 They have usually low melting and boiling point. But
large molecules with three dimensional pattern are
stable and hard so they have high melting and
boiling point.
 They are bad conductors of heat and electricity but
compounds having polar character show
conductance when dissolve in polar solvent.
 They are insoluble in water but soluble in non
aqueous solution like benzene, ether etc.

17. POLAR COVALENT BOND
 Covalent bond is form
between different type of
atoms ( Hetero-atoms)
 The bond pair of electron
will not be attracted equally.
 There is a difference of
electronegativity between
two covalently bonded
atoms.
 For example HCl, H2O,HF

18. NON POLAR COVALENT BOND
 Covalent bond is form
between same type of
atoms ( Homo-atoms)
 The bond pair of
electron will be
attracted equally.
 For example:
 H2 and Cl2

19. DIFFERENTIATE BETWEEN POLAR AND NON
POLAR COMPOUNDS
 Polar compounds
dissolve in water.
 They are good
conductor of heat and
electricity when
dissolve in polar
compounds
 Non polar compounds
do not dissolve in
water.
 They are bad
conductors of heat and
electricity
Polar compounds Non polar compounds