1. CHEMICAL BONDING

2. CHEMICAL BOND
What is a chemical bond? The force which holds the atoms together within a molecule is called a chemical bond. Why do atoms combine? To become stable and to attain the electronic configuration of nearest noble gas in the periodic table.

3. Elements want to achieve the stable electronic configuration of the nearest noble gas
Atoms tend to gain, lose or share electrons until they are surrounded by 8 electrons
Octet Rule

4. Valence Electrons
The electrons involved in bonding are called valence electrons.
Valence electrons are found in the incomplete, outermost orbital shell of an atom.
We can represent the electrons as dots around the symbol for the element.
These pictorial representations are called Lewis Structures or Lewis Dot Structures.

5. Lewis Symbols and the Octet Rule

6. Chemical Bond Formation
There are three types of chemical bonds
Ionic Bond - electrostatic attraction between ions of opposite charge (NaCl).
Covalent Bond - sharing of electrons between two atoms (Cl2).
Coordinate Bond – a combination of covalent and electrovalent bond.

7. IONIC BOND
The number of electrons donated or accepted by the valence shell of an atom of an element-so as to achieve stable electronic configuration is called-electrovalency.
Transfer of electrons
From metal to non-metal
Results in the formation of ions
Ions are held together by strong electrostatic force of attraction.

8. Ionic Bonding Formation of NaCl Sodium loses an electron to become Na+
Chlorine gains an electron to become Cl-
Na+ has an Ne electron configuration and Cl- has an Ar configuration

11. COVALENT BOND
The number of electron pairs-which an atom shares with one or more atoms-of the same or different kind to achieve stable electronic configuration is called covalency.
Mutual sharing of electrons
Between non-metallic elements
Formation of non-ionized molecules
(absence of ions)

12. Covalent Bonding Multiple Bonds
It is possible for more than one pair of electrons to be shared between two atoms (multiple bonds)
One shared pair of electrons - single bond (H2)
Two shared pairs of electrons - double bond (O2)
Three shared pairs of electrons - triple bond (N2)
- In the above examples shared pair of electrons are equally distributed and is known as Non-polar bonds.

14. Bond Polarity and Electronegativity
Electrons in a covalent bond may not be shared evenly.
Electronegativity – The ability of an atom in a molecule to attract electrons to itself.
- The periodic trend for electronegativity is up and to the right across the periodic table.

15. Bond Polarity and Electronegativity

16. Bond Polarity and Electronegativity
A chemical bond between elements with large differences in eletronegativity will shift the electrons to the atom with the higher electronegativity.
The positive end (or pole) in a polar bond is represented + and the negative pole -.
This is called a polar covalent bond.
If the electronegativity difference is small, the bond is nonpolar; if it is large, it is a polar bond.

17. Polarity of Molecule

18. Polar Covalent Bonds: Unevenly matched, but willing to share.

19. Polarity of Molecule
Water molecule is polar where shared pair of electrons are unequally distributed between hydrogen and oxygen.
The atom which attracts electrons more strongly develops a – slight negative charge.

20. Polarity of Molecules
Dipole Moments of Polyatomic Molecules

21. METHANE
A molecule of methane is non-polar whereas all the four bond C-H bonds in the molecule are polar.
Reason: The net effect of the polarity of four bonds, taking into account their directions, is zero.

22. COORDINATE BOND
Coordinate bond or Dative bond is formed by sharing of two electrons between two atoms where both the electrons of the shared pair are contributed by one atom and another atom merely participates in sharing.

23. Formation of Hydronium ion
The hydrogen ion (H+) in hydronium ion shares one lone pair of electrons of the oxygen atom of water molecule. This results in the formation of H3O+ ion.

24. Formation of Ammonium ion
The hydrogen ion (H+) in ammonium ion shares one lone pair of electrons of the nitrogen atom of ammonia molecule. This results in the formation of NH4+ ion.

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