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Polyatomic Molecule

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What are Polyatomic Molecules?

Polyatomic molecule is a very important topic of the inorganic chemistry branch. In this branch, polyatomic meaning is the most commonly asked term. Let us discuss the polyatomic meaning first. Polyatomic molecules are molecules that are composed of more than two elements or atoms.

This article has covered all the important points and concepts of the polyatomic molecule topic like polyatomic molecules examples, definition of polyatomic molecules, and different types of polyatomic molecules. Generally, polyatomic molecules are also known as compounds. 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

  • Nonpolar polyatomic molecules

  • Polar Polyatomic Molecules

In 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.

  • Non-Polar Polyatomic Molecules

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

  • Linear polyatomic molecules

  • Non-linear polyatomic molecules

  • Linear Polyatomic Molecules

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.

  • Non-linear Polyatomic Molecules

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.

N H3 + 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.

Molecular Chemistry

Molecular chemistry or molecular physics, depending on the focus, is the study of molecules. Molecular chemistry is concerned with the laws that regulate the interaction of molecules that result in the formation and breakage of chemical bonds, whereas molecular physics is concerned with the laws that govern their structure and properties. A molecule is a stable system (bound state) made up of two or more atoms in molecular sciences. Molecules have fixed equilibrium geometries—bond lengths and angles—around which they oscillate in a constant loop of vibrational and rotational motions.

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A pure material is made up of molecules with the same geometrical structure on average. The chemical formula and structure of a molecule are the two most important factors in determining its properties, particularly reactivity.

Did You Know?

  • All noble gases are an example of monoatomic gas.

  • In polyatomic molecules, the atoms are bounded by the covalent bonds.

FAQs on Polyatomic Molecule

1. What are molecular and empirical formulas?

Different molecules are identified by their molecular formula, which reflects the exact number of component atoms. Different isomers, on the other hand, can have the same atomic composition while being different molecules. The empirical formula is not always similar to the molecular formula; for example, the molecular formula for acetylene is given as C2H2, whereas, the simplest integer ratio of elements is CH.

2. Why do polyatomic ions have such a high reactivity?

New compounds and elements are formed as a result of reactions. A transfer of electrons is usually involved in the production of new material. Because polyatomic ions have a charge, they can either donate or accept electrons. As a result, they are highly reactive, as they may readily acquire or donate electrons.

3. Why are there positive and negative charges on polyatomic ions?

They're ions, after all. Ions have the charges by definition, and there are only two types of charges: positive and negative.

The charge is present in monatomic and polyatomic ions because the ion has more (negative) or fewer (positive) electrons than protons.