Halides in Chemistry – Definition, Types, and Examples

The binary compounds of halogens with other elements of the periodic table are called halides. Example NaCl, AlCl₃, CCl₄.

Classification of halides on the basis of nature of bonding:

There are three types of halides in this respect:

1. Ionic halides
2. Bridge type halides or polymeric halides
3. Covalent halides.

Ionic Halides.

Those halides in which there is ionic bond between the metal and the halogen are called ionic halides.

General formula:

\[
MX
\]

Formation Example:

\[
Na + \frac{1}{2}Cl_2 \rightarrow NaCl
\]

Here, sodium donates one electron to chlorine → Na⁺ + Cl⁻.

Explanation:
The metals of the group number I-A and II-A are sufficiently electropositive. They have low ionization energy values and hence can create the ionic bonds with F₂, Cl₂, Br₂ and l₂. Anyhow, the salts of bromides and iodides are less ionic than those of fluorides and chlorides.

General properties of ionic halides:

1. They are hard crystalline substances like NaCl.
2. They have high melting and boiling points.
3. They have three dimensional lattices consisting of discrete ions.
4. They have lattice energies, but the lattice energies of the fluorides are maximum, This is due to very small size of the fluoride ion.
5. They are soluble in H₂O.
6. They are insoluble in organic solvents.
7. They allow the electrical current to pass through them in the solution state and molten state.
8. The order of melting and boiling points is as follows: metal fluorides > metal chlorides > metal bromides > metal iodides

Polymeric halides.

Those halides which have the polymeric structure and have partially ionic bonding along with the layer of chain lattices.
Explanation:
The element like Be, Ga and Al form polymeric halides. The properties of these halides are intermediate between ionic and covalent halides.

Covalent Halides.

Those halides in which the bonds are produced due to the sharing of electrons between halogens and the other elements are called covalent halides.

General formula:

\[
E X_n
\]

where E = non-metal or metalloid, X = halogen.

Explanation:
The electronegative elements or non-metals of the periodic table are mostly responsible for such type of halides. Metalloids also give the covalent halides. For example, the elements of the group IV-A, V-A and VI-A give covalent halides.

General property of covalent halides:

1. They are mostly soluble in H₂O, but less than those of ionic halides.
2. Some of these are gases, some are liquids and majority are solids.
3. Their melting and boiling points are less than those of ionic halides.
4. Physical properties of covalent halides are influenced by the size and polarizability of the halogen atoms.
5. Iodides have the largest sizes. They have greater polarizabilities. Greater the van der waals forces higher the melting points and boiling points than other covalent halides.

Comparison Table: Ionic vs Covalent vs Polymeric Halides

Property	Ionic Halides	Covalent Halides	Polymeric Halides
Bond Type	Electrovalent	Covalent	Covalent + Coordinate
Formation	Metal + Halogen	Non-metal + Halogen	Electron-deficient halides
State	Solid	Gas/Liquid	Solid
Solubility	Soluble in water	Insoluble in water	Slightly soluble
Conductivity	Conducts in molten state	Non-conductor	Non-conductor
Hydrolysis	Stable	Often hydrolyzed	Partially hydrolyzed
Examples	NaCl, KBr, MgCl₂	CCl₄, SiCl₄, PCl₃	Al₂Cl₆, BeCl₂, Ga₂Cl₆

Conclusion.

Ionic Halides → They have strong electrostatic forces, high melting points, and are good conductors in their molten form.

Covalent Halides → They have weak forces, are volatile, and often hydrolyze.

Polymeric Halides → They have a bridged structure, intermediate properties, and are found in electron-deficient compounds.

These three halide types together show how the nature of bonding and atomic size control the physical and chemical behavior of compounds formed with halogens.

Frequently Asked Question.