Question

How can a diatomic molecule be nonpolar? Polar?

Short answer

A diatomic molecule is nonpolar if it has identical atoms and polar if it has different atoms with different electronegativities.

Step-by-step solution

Understand Diatomic Molecules

A diatomic molecule is composed of two atoms. These can be of the same element or different elements. When they are of the same element, it's often referred to as a homonuclear diatomic molecule, and when they are different, it's called a heteronuclear diatomic molecule.

Determine Nonpolarity

For a diatomic molecule to be nonpolar, it must be homonuclear (e.g., \ \(\text{H}_2, \text{O}_2\ \), etc.). In such molecules, the electrons are shared equally between the two atoms, resulting in no net dipole moment.

Determine Polarity

A diatomic molecule is polar when it consists of two different atoms (heteronuclear), and there is a significant difference in electronegativity between them. This difference causes the electrons to be unequally shared, leading to a dipole moment. A common example is \ \(\text{HCl}\ \), where chlorine is more electronegative than hydrogen.

Key concepts

Polarity

Polarity in chemistry refers to the distribution of electric charge around atoms, molecules, or chemical bonds. When discussing diatomic molecules, polarity plays a significant role in determining the molecule's properties.
Polarity arises due to differences in electronegativity between the atoms in a molecule. Electronegativity is the ability of an atom to attract the shared pair of electrons towards itself. In polar molecules, one atom will attract the electrons more strongly than the other, creating a charge separation. This results in a dipole moment, where one end of the molecule is slightly negative, and the other end is slightly positive. A common example of a polar diatomic molecule is hydrogen chloride (HCl), where the chlorine atom is more electronegative than hydrogen, pulling the shared electrons closer to itself.
In contrast, nonpolar diatomic molecules, a concept we'll explore further, have no such charge separation.

Nonpolar Molecules

Nonpolar molecules, such as some diatomic molecules, are characterized by an even distribution of electrical charge. In these molecules, the electrons are shared equally between the two atoms, resulting in no net separation of charge and, consequently, no net dipole moment.
Homonuclear diatomic molecules, like hydrogen ( ext{H}_2 ), oxygen ( ext{O}_2 ), or nitrogen ( ext{N}_2 ), are classic examples of nonpolar molecules. Since both atoms in the molecule are identical, their electronegativities are the same. This means they attract the bonded electrons equally, and there is no preferential charge on one atom over the other.
Because nonpolar molecules lack a dipole moment, they tend to interact weakly with polar substances like water, affecting how they behave in solutions.

Electronegativity

Electronegativity is a fundamental property that explains how atoms interact and form bonds. It is a measure of the tendency of an atom to attract a bonding pair of electrons. The concept of electronegativity helps in understanding the behavior of atoms in molecules, particularly in terms of bond polarity.
Each element has a specific electronegativity value, and these values can vary significantly across the periodic table. The differences in electronegativity between atoms determine the direction and magnitude of the dipole moment in a molecule. The larger the difference in electronegativity, the more polar the bond will be. In the case of heteronuclear diatomic molecules like ext{HCl} , chlorine's high electronegativity results in a polar bond with hydrogen because chlorine attracts the shared electrons more strongly.
Understanding electronegativity is crucial for predicting molecular behavior, especially in terms of interactions and reactivity with other molecules.