Electron Pair Repulsion Theory & Molecular Shapes

Flashcards covering charge clouds, VSEPR theory, repulsion hierarchy, ideal molecular shapes and bond angles, lone-pair effects, and the distinction between charge clouds and orbitals.

What is meant by a “charge cloud” in an atom or molecule?

A region of space where there is a high probability of finding an electron due to its rapid movement.

State the basic idea of electron-pair repulsion (VSEPR) theory.

Electron pairs in the outer shell of a central atom repel each other and position themselves as far apart as possible, determining molecular shape.

Differentiate between bonding pairs and lone pairs of electrons.

Bonding pairs are shared between two atoms to form a bond, whereas lone pairs are non-bonding electrons localized on a single atom.

Compare the relative repulsion strengths of electron pairs in a molecule.

Lone pair–lone pair > lone pair–bonding pair > bonding pair–bonding pair.

Give the shape and bond angle for a molecule with two charge clouds around its central atom.

Linear; bond angle 180° (e.g., CO₂).

Give the shape and bond angle for a molecule with three charge clouds around its central atom.

Trigonal planar; bond angle 120° (e.g., BF₃).

State the shape and all bond angles for a molecule with five charge clouds.

Trigonal bipyramidal; bond angles 90° and 120° (e.g., PCl₅).

How does the presence of one lone pair change the ideal tetrahedral bond angle?

Each lone pair reduces the ideal 109.5° by about 2.5°, giving ~107° (as in NH₃).

What is the molecular geometry and approximate bond angle of H₂O, and why?

Bent (V-shaped) with bond angle ~104.5° because two lone pairs on oxygen compress the angle from the tetrahedral value.

Explain why double or triple bonds count as one ‘charge cloud’ in VSEPR counting.

Regardless of the number of shared electrons, a multiple bond occupies one region of electron density, so it is counted as a single charge cloud.

Why do electron pairs adopt 3-D arrangements rather than remain in a plane?

Electrostatic repulsion forces negatively-charged electron pairs to maximize separation in three dimensions for minimum repulsion energy.

Distinguish between the terms ‘charge cloud’ and ‘orbital’.

A charge cloud is a broad region where electrons are likely to be found (bonding or lone pairs), whereas an orbital is a specific quantum-mechanical wavefunction describing an individual electron’s probable location.