Homonuclear Diatomic Molecules

Homonuclear diatomic molecules are composed of two identical atoms and are relatively simple in structure. Molecular orbital theory, a method for describing the behavior of electrons in a molecule, can be used to understand the bonding and properties of these molecules. Understanding the properties of homonuclear diatomic molecules is essential for understanding the behavior of more complex molecules and materials. In this article, we will look into what are homonuclear diatomic molecules, their examples, etc.

What are Homonuclear Diatomic Molecules?

Homonuclear diatomic molecules are composed of two identical atoms. They exhibit a nonpolar bond and are characterized by their simplicity in structure. They play a fundamental role in molecular orbital theory, where atomic orbitals from each atom combine to form molecular orbitals. Understanding homonuclear diatomic molecules is crucial for predicting properties like bond order, bond length, and bond energy. These molecules are essential in chemistry as they serve as building blocks for more complex compounds and materials, providing insights into chemical bonding and reactivity.

Forces between Homonuclear Diatomic Molecules

The force between homonuclear diatomic molecules depends on several factors, including the nature of the bonding between the atoms, the distance between the molecules, and any external influences such as temperature and pressure. The different types forces that exist between homonuclear diatomic molecules are:

• Covalent Force
• Vanderwaals Force
• London Force
• Dipole-Dipole Interaction

Examples of Homonuclear Diatomic molecules

Homonuclear diatomic molecules are composed of two identical atoms, while heteronuclear diatomic molecules are composed of two different atoms. Here are some examples of homonuclear diatomic molecules:

Hydrogen (H₂)

Hydrogen (H₂) is the most abundant diatomic molecule in the universe, and it is composed of two hydrogen atoms. The bond in H₂ is a covalent bond where the electrons are shared equally between the two hydrogen atoms. The bond order of H₂ is 1, indicating a single bond between the two hydrogen atoms. A H₂ molecule has two electrons

MOT electronic configuration:

(σ1s)²

Number of electrons in Bonding = 2

Number of electrons in Antibonding = 0

Bond order = (Number of electrons in Bonding – Number of electrons in Antibonding)/2 = (2-0)/2 = 1

Hydrogen (H₂) is a homonuclear diatomic molecule with two electrons in the σ bonding molecular orbital and none in the σ* antibonding molecular orbital. Therefore, the bond order of H₂ is 1, and it is diamagnetic, meaning it is not attracted to a magnetic field.

Oxygen (O₂)

Oxygen (O₂) is a colorless, odorless, and tasteless gas that makes up about 21% of the Earth’s atmosphere. The bond in O₂ is a double bond, indicating a strong bond between the two oxygen atoms. A O₂ molecule has 16 electrons

MOT electronic configuration:

(σ1s)²(σ*1s)²(σ2s)²(σ*2s)²(σ2p_z)²(π2p)⁴(π*2p)²

Number of electrons in Bonding = 10

Number of electrons in Antibonding = 6

Bond order = (Number of electrons in Bonding – Number of electrons in Antibonding)/2 = (10-6)/2 = 2

Bond order: 2

Oxygen (O₂) is a homonuclear diatomic molecule with four electrons in the σ bonding molecular orbital, four electrons in the π bonding molecular orbital, and two electrons in the π* antibonding molecular orbital. Therefore, the bond order of O₂ is 2, and it is paramagnetic, meaning it is attracted to a magnetic field.

Nitrogen (N₂)

Nitrogen (N₂) is a colorless, odorless, and tasteless gas that makes up about 78% of the Earth’s atmosphere. The bond in N2 is a triple bond, indicating a strong bond between the two nitrogen atoms. A N2 molecule has 14 electrons.

MOT electronic configuration:

(σ1s)²(σ*1s)²(σ2s)²(σ*2s)²(π2p)⁴(σ2p)²

Number of electrons in Bonding = 10

Number of electrons in Antibonding = 4

Bond order = (Number of electrons in Bonding – Number of electrons in Antibonding)/2 = (10-4)/2 = 3

Bond order: 3

Nitrogen (N₂) is a homonuclear diatomic molecule with four electrons in the σ bonding molecular orbital, four electrons in the π bonding molecular orbital, and two in the σ* antibonding molecular orbital. Therefore, the bond order of N₂ is 3, and it is diamagnetic.

Fluorine (F₂)

Fluorine (F₂) is a pale yellow gas that is highly reactive and toxic. The bond in F₂ is a single bond, indicating a weak bond between the two fluorine atoms. A F2 molecule has 18 electrons

MOT electronic configuration:

(σ1s)²(σ*1s)²(σ2s)²(σ*2s)²(σ2p_z)²(π2p)⁴(π*2p)⁴

Number of electrons in Bonding = 10

Number of electrons in Antibonding = 8

Bond order = (Number of electrons in Bonding – Number of electrons in Antibonding)/2 = (10-8)/2 = 1

Bond order: 1

Fluorine (F₂) is a homonuclear diatomic molecule with four electrons in the σ bonding molecular orbital, four electrons in the π bonding molecular orbital, and two in the σ* antibonding molecular orbital and four electrons in the π* antibonding molecular orbital. Therefore, the bond order of F₂ is 1, and it is diamagnetic.

Lithium (Li₂)

Lithium molecule (Li₂) is a homonuclear diatomic molecule, which is composed of two identical lithium atoms. A Li2 molecule has six electrons.

MOT electronic configuration:

σ1s² σ*1s² σ2s²

Number of electrons in Bonding = 4

Number of electrons in Antibonding = 2

Bond order = (Number of electrons in Bonding – Number of electrons in Antibonding)/2 = (4-2)/2 = 1

The bond order of Li₂ is (4-2)/2 = 1.

This means the bond between the two lithium atoms is relatively weak, and the molecule is expected to be unstable. However, Li₂ molecules have been observed in the vapor phase, indicating they can exist under certain conditions.

The magnetic behavior of diatomic molecules depends on the number of unpaired electrons in the molecule. Since Li₂ has no unpaired electrons, it is expected to be diamagnetic, meaning it is not attracted to magnetic fields.

Difference between Homonuclear and Heteronuclear molecules

The difference between Homonuclear and Heteronuclear molecules are as follows:

Characteristic	Homonuclear Diatomic Molecules	Heteronuclear Diatomic Molecules
Composition	Composed of two identical atoms of the same element	Composed of two different atoms of different elements
Electronegativity	Atoms have the same electronegativity	Atoms have different electronegativities
Bond Type	Can have single, double, or triple bonds	Can have ionic or covalent bonds
Symmetry of Atoms	Atoms are the same	Atoms are different
Examples	Hydrogen (H2), Nitrogen (N2), Oxygen (O2)	Hydrochloric acid (HCl), Carbon monoxide (CO)

Magnetic Properties of Homonuclear Diatomic Molecules

Homonuclear diatomic molecules can exhibit different magnetic properties depending on factors such as the electronic configuration and the nature of the bond between the atoms. The magnetic properties of homonuclear diatomic molecules can be categorized into two main types:

Paramagnetic Properties

• Paramagnetic substances have unpaired electrons in their molecular orbitals, which results in the presence of magnetic moments.
• In homonuclear diatomic molecules, if the molecule has one or more unpaired electrons, it exhibits paramagnetic behavior.
• For example, molecules like oxygen (O₂) have unpaired electrons in their molecular orbitals, making them paramagnetic.

Diamagnetic Properties

• Diamagnetic substances have all their electrons paired up in their molecular orbitals, resulting in the absence of magnetic moments.
• In homonuclear diatomic molecules, if all electrons are paired, the molecule exhibits diamagnetic behavior.
• For example, molecules like nitrogen (N₂) in their ground state have all electrons paired, making them diamagnetic.

FAQs on Homonuclear Diatomic molecules

What are homonuclear diatomic molecules?

Homonuclear diatomic molecules are molecules composed of two atoms of the same element bonded together, like O₂ (oxygen gas) or N₂ (nitrogen gas).

What are the seven homonuclear diatomic molecules?

The seven homonuclear diatomic molecules are hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂).

What is the difference between homonuclear and heteronuclear diatomic molecules?

Homonuclear molecules consist of two atoms of the same element, while heteronuclear molecules, like CO (carbon monoxide), contain two different elements bonded together.

What is the molecular orbital theory?

Molecular orbital theory explains how electrons are distributed in molecular orbitals formed by the overlapping of atomic orbitals during bond formation

What is the bond length of a molecule?

The bond length of a molecule refers to the distance between the nuclei of the bonded atoms, representing the equilibrium distance where the attractive and repulsive forces between the atoms are balanced.

Is He₂ molecule possible?

The bond order of He₂ molecule is zero. Hence, He₂ molecule doesn’t exist.