Answer to Question #310356 in Inorganic Chemistry for Almas

Question

Write a detail note on Polyatomic Molecule

Answer 1

Polyatomic molecules are molecules that are composed of more than two elements or atoms. Polyatomic atoms combine with different kinds of forces and form the compound.

Polyatomic Molecules Examples

Some of the polyatomic molecules examples are given below:

Glucose

Carbon dioxide

Sulphur dioxide

Sulphur tetrafluoride

Hexane

Propane

Sulphuric acid

Nitric acid

Phosphoric acid

Types of Polyatomic Molecule

Classification Based on the Polarity of the Molecule

Polar polyatomic molecules, the atoms of different electronegativities are present. The electronegativity difference is high between the atoms of these polar polyatomic molecules. Examples of polyatomic elements of polar types are nitric acid, sulphuric acid, and phosphoric acid.

In nonpolar polyatomic molecules, the atoms of similar electronegativity are present. The electronegativity difference is very low or zeroes in these nonpolar polyatomic molecules. Examples of nonpolar polyatomic molecules are ozone, carbon dioxide, and methane.

Classification Based on the Shape of the Molecule

Polyatomic molecules that are linear in shape are known as linear polyatomic molecules. The atoms in these linear molecules are arranged in a straight line (at an angle of 180 degrees). At the central atom of linear geometry polyatomic molecules, the electron pair has sp hybridization. Carbon dioxide (O=C=O) and beryllium hydride H-Be-H are examples of linear electron pairs and molecular geometry.

Compounds of non-linear polyatomic geometry are known as nonlinear polyatomic molecules. This means that the atoms in these molecules aren't organized in a straight line, and the molecules aren't linear. The hybridization of the atomic orbitals of the atoms in the molecule determines the shape of these molecules. Methane, ozone, benzene, phosphene, and the water molecule are nonlinear polyatomic examples.

Molecular Orbital of Polyatomic Molecules

In the polyatomic molecules, the orbitals of peripheral atoms combine to form group orbitals. Now, these group orbitals combine with orbitals of the central atom to form molecular orbitals. Let us take the example of BeH₂.

In BeH₂ two hydrogen atoms (peripheral atoms) combines with the beryllium atom (central atom).

H + H → H₂

Here in the above reaction, H has a single orbital and the orbital of the H₂ molecule is known as the group orbital. Now, this group orbital will combine the orbital of beryllium to form the molecular orbital of the BeH₂.

H₂ + Be → BeH₂

The correct combinations can be obtained by considering matching algebraic signs of the orbitals of the central atom and peripheral atoms. Such combinations are known as symmetry-adapted linear combinations. In short, symmetry-adapted linear combinations can be written as SALCs. The above molecular orbital formation of the beryllium dihydride represents that the two hydrogen atoms combine with the beryllium to form beryllium dihydride. It is a triatomic linear molecule.

Electronic Configurations of Atoms

Electronic configuration of hydrogen (H) = 1s¹.

Electronic configuration of beryllium (Be) = 1s², 2s².

As we know in beryllium dihydride, the beryllium is taken as a central atom and hydrogen atoms are taken as a side or peripheral atom.

Polyatomic Charged Molecules

The charged polyatomic molecules are known as polyatomic ions. The ion is an entity that consists of a charge. Ions are generally formed by the loss or gain of an electron. They attain the noble gas configuration and extra stability by converting into ions. Let us see this with some examples.

Cl + e^- → Cl^-

In the above reaction, the chlorine atom gains an electron and forms a charged entity. This single charge entity is known as a monatomic ion. The negative charge is present on chlorine atoms.

H₂O → H⁺ + OH^-

In the above reaction, the water molecule dissociates to form a hydronium ion and hydroxyl ion. The hydroxyl ion (OH^-) represents the diatomic ion.

NH₃ + H⁺ → NH₄⁺

Ammonium ion (NH₄⁺) is an example of a polyatomic ion. The positive charge present in the ammonium ion is distributed on the whole molecule. A polyatomic ion is a charged entity that is composed of several atoms bound together.

Polyatomic Molecules Properties

Polyatomic molecules are made up of three or more atoms in a stable structure (bound state).

Different molecules are identified by their molecular formula, which reflects the exact number of compositional atoms.

The empirical formula and the molecular formula are often, but not always, the same.

Electrically neutral groups of three or more atoms are held together by covalent bonds in polyatomic molecules. Molecules differ from ions in that they do not have an electrical charge.