INTRODUCTION TO CHEMICAL BONDS
Definition: A chemical bond is defined as a force that acts between two or more atoms to hold them together as a stable molecule.
Main types of bond:
1. Ionic or electrovalent bond,
2. Covalent bond,
3. Coordinate covalent bond
Forth type of bond:
Metallic bond: The type of bonding which holds the atoms together in metal crystal.
Valence electron: The electrons in the outer most energy level in an atom that takes part in chemical bonding are called valence electrons. Bonding electrons: The valence electrons actually involved in bond formation are called bonding electrons. Octet rule: In chemical bond formation, atoms interact- (i) by losing, (ii) by gaining or (iii) by sharing electrons to acquire a stable noble gas configuration. He (2) 2
Ne (10) 2, 8
Ar (18) 2, 8, 8
Kr (36) 2, 8, 18, 8
Xe (54) 2, 8, 18, 18, 8
Rn (86) 2, 8, 18, 32, 18, 8
The tendency for atoms to have eight electrons in the outer shell is known as Octet rule.
Definition: The electrostatic attraction between the cation (+ve ions) and anions (-ve ions) produced by electron transfer constitutes an ionic or electrovalent bond.
Conditions for formation of ionic bond:
1) Bond formations occur between the metal and nonmetal. Metal is donor and nonmetal is acceptor. 2) Net lowering of energy:
To form a stable ionic compound, there must be a net lowering of the energy. For example- formation of NaCl molecule (a) Na ― e → Na+ ―119 kcal
(b) Cl + e → Cl‾ +85 kcal
(c) Na+ + Cl‾→ Na+ Cl‾ +187 kcal
Net energy released, 187 + 85 ― 119 = 153 kcal
This causes lowering of energy of the process, hence ionic bond formed.
3) Electro negativity difference between the atoms
Na → 0.9
Cl → 3.0
Difference, 3.0 ― 0.9 = 2.1
Hence ionic bond will form.
Factors that govern the formation of ionic bond:
1) Ionization energy,
2) Electron affinity,
3) Lattice energy
Some examples of ionic bond:
Characteristics of ionic compounds:
1) solids at room temperature
2) high melting and boiling points
3) hard and brittle,
4) soluble in water but insoluble in organic solvents,
5) conductors of electricity,
6) don’t exhibit isomerism
7) undergo ionic reactions which are fast.
Definition: The attractive force between atoms created by sharing of an electron-pair.
Conditions for formation of covalent bond:
1) Bond formations occur between two same or different nonmetals. 2) Equal electronegativity
3) Equal sharing of electrons
Some examples of covalent compounds:
Examples of multiple covalent bonds:
Characteristics of covalent compounds:
1) Gases, liquids or solids at room temperature,
2) Low melting points and boiling points,
3) Soft, much readily broken,
4) Insoluble in water but soluble in organic solvents,
5) Non-conductors of electricity,
6) Exhibit isomerism,
7) Undergo molecular reactions which are generally slow
COORDINATE COVALENT BOND
Definition: A covalent bond in which both electrons of the shared pair come from one of the two atoms (or ions). Examples:
Definition: A metallic bonding is the electrostatic force of attraction.
Electric conductivity: By displacement of electron as a result of voltage at both ends.
Heat conductivity: By absorbing heat energy and increasing vibrational motion of electron which collide with adjacent electron and transfer energy
Ductility (that can be made into thin wire) and Malleability (can be pressed into different shapes without breaking):
When hydrogen (H)...
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