CHEMICAL BONDING

A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds.

IONS

An ion is an electrically charged species.A positively charged ion is called cation,while a negatively charged ion is called anion.A cation contains less electrons than a normal atom while an anion contains more electron than a normal atom.

e.g., cation Na⁺,H⁺,Mg²⁺ and anion Cl^-,F^-,I^-.

The metal atom lose electron to form cations and non-metal atom accept electrons to form anions.There is no charge in atomic number or number of protons when an atom forms ion.

ISOELECTRONIC SPECIES

Species having the same number of electrons but different nuclear charge are known as isoelectronic species.They also have same bond order.

TYPES OF CHEMICAL BOND

CHEMICAL BONDING

ELECTROVALENT BOND OR IONIC BOND

The bond is formed by the transfer of electrons from one atom to another.

These bonds are formed between metals and non-metals.

Properties of electrovalent compounds are

(a) These are usually crystalline solids.

(b) These have high melting point.

(d) These are insoluble in organic solvents like alcohol etc.

(e) If the electronegativity difference of two atoms is 1.7,the bond between them is fifty per cent ionic.

SOME ELECTROVALENT COMPOUNDS

NAME	FORMULA	IONS PRESENT
Aluminium oxide (Alumina)	Al₂O₃	Al³⁺,O^2-
Ammonium chloride	NH₄Cl	NH₄⁺ and Cl^-
Calcium chloride	CaCl₂	Ca²⁺ and Cl^-
Calcium nitrate	Ca(NO₃)₂	Ca²⁺ and NO₃^-
Copper sulphate	CuSO₄	Cu²⁺ and SO₄^2-
Magnesium chloride	MgCl₂	Mg²⁺ and Cl^-
Magnesium oxide	MgO	Mg²⁺ and O^2-
Potassium chloride	KCl	K⁺ and Cl^-
Sodium chloride	NaCl	Na⁺ and OH^-
Sodium hydroxide	NaOH	Na⁺ and OH^-

COVALENT BOND

This bond is formed by the sharing of electrons between two atoms.

When a non-metal combines with another non-metal, a covalent bond is formed.

The bond formed between the atoms of the same elements is also a covalent bond.

Covalent bonds are of three types:

Single covalent bond (by sharing of one pair of electrons)

Double covalent bond (by sharing of two pairs of electrons)

Triple covalent bond (by sharing of three pairs of electrons)

Properties of covalent compounds are:

These are usually liquids or gases,having usually low melting point and boiling point.

These do not conduct electricity and are insoluble in water but dissolve in organic solvents.

These show stereoisomerism because covalent bond is directional in nature.

SOME COVALENT COMPOUNDS

NAME	FORMULA	ELEMENTS PRESENT
Alcohol (Ethanol)	C₂H₅OH	C,H and O
Ammonia	NH₃	N and H
Acetylene (Ethyne)	C₂H₂	C and H
Carbon dioxide	CO₂	C and O
Carbon disulphide	CS₂	C and S
Carbon tetrachloride	CCl₄	C and Cl
Cane sugar	C₁₂H₂₂O₁₁	C,H and O
Ethane	C₂H₆	C and H
Ethylene	C₂H₄	C and H
Glucose	C₆H₁₂O₆	C,H and O
Methane	CH₄	C and H

COORDINATE BOND

This type of bond is formed by one sided sharing of one pair of electrons between two atoms.

The atom having completed octet which provides the electron pair for sharing is known as donor.

The other atom which accept the electron pair is called the acceptor atom.

HYDROGEN BOND

This bond is electrostatic force of attraction between hydrogen atom covalent bonded to a highly electronegative atom and any other electronegative atom which is present in the same or different molecules.

It is mainly of two types:

Intermolecular H-bonding (e.g., H₂O,HF,NH₃ molecule)

Intramolecular H-bonding (e.g.,o-nitrophenol)

Molecules having O-H,N-H or H-F bond show abnormal properties due to H-bond formation.