Beginner Topic 125 of 1102 Bonding & Molecular Structure
Lone Pairs
Pairs of valence electrons not involved in bonding that occupy space around an atom.
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In-depth explanation of Lone Pairs
A lone pair is a pair of valence electrons that belongs to one atom and is not used in bonding. Lone pairs occupy more space than bonding pairs because they are held by only one nucleus and so spread out more. This extra repulsion compresses the angles between neighbouring bonds and influences the overall shape of a molecule. Lone pairs also determine polarity and allow atoms such as nitrogen and oxygen to act as Lewis bases, donating to protons or metal ions. They are shown explicitly in Lewis structures and in VSEPR counting.
Going deeper: Lone Pairs
Key ideas: To count lone pairs on an atom: valence electrons minus the number of bonds it forms (for neutral atoms obeying the octet). Oxygen with 2 bonds has 2 lone pairs, nitrogen with 3 bonds has 1, and a halogen with 1 bond has 3. Lone pairs count as electron domains in VSEPR, and they are the nucleophilic or basic sites in a molecule.
Common mistakes and connections: A common mistake is leaving lone pairs off a drawing, which hides the geometry and the reactivity, or failing to count them as a domain. Another is believing lone pairs and bond pairs repel equally. Connects to VSEPR angle deviations, Lewis basicity and coordinate bonds.
Visualization of Lone Pairs
Oxygen in water carries two lone pairs besides its two O-H bonds. Lone pairs take more room than bonding pairs and squeeze the H-O-H angle below 109.5 degrees. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Water has two lone pairs on oxygen, which makes the molecule bent with an H-O-H angle of 104.5 degrees.
Frequently asked questions about Lone Pairs
What is Lone Pairs?
Pairs of valence electrons not involved in bonding that occupy space around an atom.
Is Lone Pairs a beginner, intermediate or advanced topic?
Lone Pairs is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Lone Pairs?
Study these earlier topics in Bonding & Molecular Structure first: Lewis Dot Symbols, Lewis Structures, Single Double and Triple Bonds.
What comes after Lone Pairs?
The next topics in Bonding & Molecular Structure are Formal Charge and Resonance.
Can I practise Lone Pairs with quizzes?
Yes. The interactive lesson includes a self-check question on Lone Pairs, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Where Lone Pairs fits in Bonding & Molecular Structure
Lone Pairs is topic 10 of 104 in Bonding & Molecular Structure.