What are Diatomic Molecules? (2023)

Diatomic molecules are molecules with two atoms in their structure. They can be two atoms attached to a nucleus or two atoms attached to more than one nucleus (heteronuclear).

The world of the very small dictates the qualities exhibited by the world of the very large. This "little world" is inhabited by atomic and subatomic particles.

Atoms can be thought of as Lego pieces; They are combined in different ways to do different things. So the same Lego bricks can build a boat or a bridge as atoms can build a blade of grass or a giraffe.

When two or more atoms join together, they form a molecule. The number of atoms in a molecule denotes the prefix, therefore a molecule containing two atoms is said to be diatomic.

There are different types of diatomic molecules. Let's start this discussion with a better understanding of how a molecule works.

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molecules

Molecules are the constituents of matter; They are the smallest particles that exhibit the chemical properties of the element to which they belong. Molecules can be homonuclear, meaning they can be made up of atoms of only one chemical element (for example, hydrogen (H₂)), or they can be heteronuclear, meaning they can be a chemical compound with atoms of more than one element (for example, water (H₂Ö)).

Molecules are formed when two or more atoms are held together by chemical bonds. This bond represents a permanent attraction between molecules, ions and atoms. This bond can be the result of the attraction of oppositely charged ions or the sharing of electrons between two atoms.

Atoms are stable when their outer shell is full or empty. To be considered full, it must have 8 electrons in the outer shell called the octet. When this is not the case, atoms combine to gain or lose an electron from another atom or share pairs of electrons with another atom.

This transaction of electrons gives way to chemical bonds:

ionic compound

This bond occurs when electrons are completely transferred from one atom to another. This creates two ions, the atoms that have gained one or more electrons are called anions (negatively charged) and those that have lost one or more electrons are called cations (positively charged).

Take the case of NaCl (table salt). Chlorine contains 7 electrons in its outer shell and needs one to complete its octet. Sodium has 1 electron in its outer shell, which it donates to chlorine to form an ionic bond.

Covalent bond

A covalent bond occurs when two atoms share pairs of electrons; it is also the strongest of chemical bonds. This exchange of electrons helps the atoms reach their stable state.

There are two main types of covalent bonds: nonpolar and polar covalent bonds. Nonpolar or purely covalent bonds are formed between atoms that have the same electronegativity and therefore share electrons equally. This is observed for atoms with an electronegativity difference of less than 0.4.

When the electronegativity difference is between 0.4 and 1.7, the bond becomes polar. In this case, the electrons spend more time, on average, in the atom with the higher electronegativity. For example, in water (H2O), on average, electrons are associated with oxygen (O) most of the time, giving it a partial negative charge and hydrogen (H) a partial positive charge.

diatomic molecules

Molecules with two atoms of the same or different chemical elements are called diatomic. Almost all diatomic elements are gases (eg, hydrogen, nitrogen) at room temperature. Some elements become diatomic at higher temperatures.

Diatomic molecules of nitrogen (78%) and oxygen (21%) make up the majority of Earth's atmosphere. At an interstellar level, the diatomic molecule of hydrogen is the most abundant in the entire universe.

Types of Diatomic Molecules

Diatomic molecules can be two atoms sharing a nucleus, usually composed of the same element, or two atoms in two nuclei of two different elements.

Homonuclear Diatomic Molecules

Also read:What is the difference between a molecule and a compound?

Homonuclear molecules consist of atoms of a single element. The only elements that form diatomic molecules at room temperature are gases. These are:

Hydrogen – H₂

Hydrogen is abundant throughout the universe. A hydrogen atom consists of a single valence electron in its outer shell. To become stable, the hydrogen atom needs one more electron to complete its shell. It does this by sharing a proton with another hydrogen atom through a nonpolar covalent bond, making it a diatomic molecule.

Nitrogen – N₂

Nitrogen is the most prominent element in Earth's atmosphere. A nitrogen atom consists of 5 valence electrons in its outermost shell. To create a stable compound, two nitrogen atoms bond together and share three electrons from the opposite atom, leaving 8 electrons in the bottom shell. This becomes a diatomic nitrogen molecule with nonpolar covalent bonds between the two atoms.

oxygen-o₂

Oxygen is readily found in Earth's atmosphere, as well as in the general composition of the universe. An oxygen atom consists of 6 valence electrons in its outermost shell. It shares two electrons with another oxygen atom through a nonpolar covalent bond to become a stable diatomic molecule.

Flúor – F₂

Fluorine is a highly toxic glowing gas with a pungent odor that exists as a diatomic molecule at room temperature. The outermost shell of a fluorine atom contains 7 valence electrons. It shares an electron with another fluorine atom through a nonpolar covalent bond to become stable and form a diatomic fluorine molecule.

Cloro – Cl₂

Chlorine is a highly reactive element that is greenish-yellow in color and exists as a gas at room temperature. It consists of 3 electron shells and has 7 electrons in its outermost shell. It shares an electron with another chlorine atom through a nonpolar covalent bond to form a stable diatomic chlorine molecule.

brom-br₂

At room temperature, bromine is a reddish-brown liquid. When the temperature increases, this element forms diatomic molecules and becomes a gas. The outermost shell consists of 7 electrons and needs one to stabilize and form Br._2.

iodine - I₂

At room temperature, iodine exists as a purple-black, nonmetallic solid. Similar to bromine, forms a diatomic I₂molecule when heated. An iodine atom shares an electron with another atom to complete its octet and become stable.

Heteronuclear Diatomic Molecules

Atoms that combine with atoms of other elements to become stable and form diatomic molecules are heteronuclear. Many elements can combine to form these heteronuclear diatomic molecules under favorable conditions.

Some examples are:

Clorwasserstoff – HCL

This is a colorless gas at room temperature and forms white fumes (hydrochloric acid) on contact with the atmosphere. A hydrogen atom has one electron in its outermost shell and chlorine has 7, so they form a covalent bond to complete the octet and become a stable diatomic molecule.

Carbon Monoxide - CO

Carbon monoxide is a flammable gas that is odorless, colorless, and tasteless. It is slightly less dense than air. Carbon has 4 and oxygen has 6 valence electrons in the outermost shell. Atoms form a triple bond to become stable, thus becoming a heteronuclear diatomic molecule.

Nitric Oxide - NO

Nitrous oxide is a colorless gas. A nitrogen atom has 5 valence electrons in the outermost shell and oxygen has 6, so they combine to form stable diatomic molecules. One electron is left unpaired, making nitric oxide a free radical.

Also read:What is the octet rule?

Finally

Some of the most abundant and common elements on our planet are diatomic molecules. Diatomic molecules, ranging from the homonuclear to the heteronuclear categories, represent a stable state for elements due to the strong chemical bonds that form between valence electrons.

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