Illustrated · 2 min
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Learn About Electron Lone Pairs and Bonding Pairs
Review Electrons
Electrons are negatively charged parts of atoms. Electrons exist in a space surrounding the nucleus or center of the atom. The outermost electrons of an atom are called valence electrons. They participate in chemical reactions and form bonds. Electrons are usually found in pairs. The electrons are distinguished from each other by their spins. The two types of spins are called "spin-up" and "spin-down". In the quantum mechanical model, they have a quantum number of plus or minus one-half. This allows them to obey the Pauli Exclusion Principle and the Aufbau Principle.
Defining Lone Pairs and Bonding Electron Pairs
The valence electrons of an atom can contain up to eight electrons. But, there are exceptions depending on if the element has access to the d-orbitals. When atoms form bonds with other atoms, a molecule or compound is created. The bonds between atoms are made up of electrons from the valence electrons. The valence electrons of the atoms can either participate in bonding or not. These two electron distinctions are:
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Lone pairs - electrons that do not participate in bonding also called non-bonded pairs.
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Bonding Pairs - electrons shared with another atom to create a bond, also known as a covalent bond.
These are examples of chemical species and their electrons drawn in a dot structure. Here we can see the electrons defined as lone pairs and bonding pairs.
Image source: By Cassie Gates
In the picture above, we see molecules drawn as their lewis dot structure. The first molecule is the organic compound methane. It has four carbon-hydrogen single bonds that complete the octets. So, it has zero lone pairs. Next, we see diatomic fluorine. It only needs one single bond to complete its octet. So, it has six lone pairs. Three on each fluorine. Finally, we have the noble gas, neon. It already has a full octet. So it has four lone pairs.
Remember that when two electrons are shared, this is called a single covalent bond. A single covalent bond is also a sigma bond. The sharing of four electrons creates double bonds. A triple bond is made of six shared electrons. Double and triple bonds contain both sigma and pi bonds.
Note that when we talk about lone or bonding electrons, we refer to covalent bonds. Ionic bonds have a transfer of electrons to produce ions. So, we don't think in terms of electron pairs.
Importance of Bonding Pairs and Lone Pairs
The valence shell electron pair repulsion model (VSEPR) model relies on the idea that electron pairs repel each other. This causes bonding and lone pair electrons to stay as far away from each other as possible. The electron pair repulsion gives rise to the geometry of the molecules and compounds. Make sure to check out VSEPR Theory and molecular geometry to learn more!
