Molecular Geometry: The Full VSEPR Shapes Chart

The VSEPR chart

Here is the whole thing on one page: every standard VSEPR class from two electron domains up to six, with the shape it produces and the angle that goes with it. Domains is bonds plus lone pairs on the central atom. Class is the same information written in AXE notation. The example column gives a real molecule and its measured angle, which is usually a degree or two off the ideal because lone pairs push harder than bonds.

Three things worth noticing before you memorise anything:

• The electron geometry column depends only on the domain count. Four domains always arrange themselves tetrahedrally, no matter how many are lone pairs.
• The molecular shape column is what changes. Lone pairs are invisible, so each one you add renames the shape without moving the domains.
• Linear appears twice, at the top and again at AX₂E₃. Three lone pairs in a trigonal bipyramid all take the roomy equatorial seats, which pushes the two atoms to opposite poles and opens the angle back out to a full 180°.
• The ideal domain angle is the angle between domains, and it too depends only on the count. The angle in brackets in the example column is what is actually measured between the atoms. The two drift apart as you go down the chart, and that gap is the lone pairs doing their work.

What VSEPR theory says

The idea behind VSEPR (Valence Shell Electron Pair Repulsion) is simple: negative charges repel, so the groups of electrons around a central atom push each other as far apart as they can. Whatever 3D arrangement keeps those groups farthest apart is the shape the molecule takes. To use it you only need one thing: an accurate Lewis structure that tells you how many electron groups surround the central atom.

The number VSEPR actually cares about is the count of electron domains: every bond plus every lone pair on the central atom. A key rule: a double or triple bond still counts as one domain, because the extra electrons share the same direction in space. So:

electron domains = bonding regions + lone pairs on the central atom

For carbon dioxide (CO₂) the central carbon has two double bonds and no lone pairs, giving 2 domains and a linear, 180° shape.

Electron geometry is not molecular shape

This is the distinction that costs the most marks, and the chart above makes it visible: two columns, two different answers, from the same molecule.

Electron geometry names the arrangement of all the domains. Molecular geometry, the molecular shape, names the arrangement of the atoms only. A lone pair still occupies space and still does the pushing, but it is not an atom, so it does not get counted when the shape is named.

Water (H₂O) is the standard case. The oxygen has 2 bonds plus 2 lone pairs, giving 4 domains, so the electron geometry is tetrahedral. Erase the two lone pairs and what is left is three atoms in a V, so the molecular shape is bent. Both answers are correct; they answer different questions. If a question does not say which it wants, it wants the molecular shape.

Reading AXE notation

AXE notation is shorthand for the two numbers you counted:

• A is the central atom.
• X is an atom bonded to it, and the subscript is how many.
• E is a lone pair on the central atom, and the subscript is how many.

So AX₂E₂ means two bonded atoms and two lone pairs, which is water. AX₄ means four bonded atoms and nothing else, which is methane. Some textbooks use B where others use X and call the same system ABE notation, so AB₂E₂ and AX₂E₂ are the same molecule; a few write AB₄L for four bonds and a lone pair. The letters differ, the counting does not.

The notation is useful precisely because it throws the chemistry away. AX₄E is a seesaw whether it is SF₄ or anything else with four bonds and one lone pair. The By domain count mode in the tool above works this way round: set the two numbers, get the class, the shape and a real molecule that has it.

How lone pairs change the shape

This is the heart of the topic. Three molecules all have four electron domains, yet their shapes differ because of lone pairs:

• CH₄ (methane): 4 bonds, 0 lone pairs → AX₄ → tetrahedral, 109.5°
• NH₃ (ammonia): 3 bonds, 1 lone pair → AX₃E → trigonal pyramidal, 107°
• H₂O (water): 2 bonds, 2 lone pairs → AX₂E₂ → bent, 104.5°

A lone pair is held by just one atom, so it billows outward and pushes harder than a bonding pair (which is pinned between two nuclei). Each lone pair you add squeezes the remaining bonds a little closer together, shaving the angle down step by step. The geometry name describes only the atoms you can see, even though the lone pairs are doing the steering.

The same pattern runs through the five- and six-domain rows, just with more shapes to name. Take the octahedral SF₆ at a clean 90°, swap one fluorine for a lone pair and you get square pyramidal BrF₅ at 84.8°; swap a second and the two pairs move opposite each other, above and below, flattening the rest into square planar XeF₄ back at exactly 90°.

From domains to the angle

Once you know the domain count, the ideal angles follow a fixed menu: 2 domains → 180°, 3 → 120°, 4 → 109.5°, 5 → 90° and 120° (trigonal bipyramidal), 6 → 90° (octahedral). Lone pairs then nudge the observed angle below the ideal, with two exceptions you can see in the chart: when the lone pairs are symmetric enough to leave the atoms exactly opposite (AX₂E₃, 180°) or exactly square (AX₄E₂, 90°).

The central atom’s hybridization tracks the same count (sp for 2 domains, sp² for 3, sp³ for 4, sp³d for 5, sp³d² for 6), which is why valence electrons and the Lewis dot picture feed straight into the shape. Shape, in turn, decides whether bond dipoles cancel, which sets a molecule’s overall polarity.

Every molecule here, and its shape

If you came looking for one specific answer, it is in this table. Each row is a molecule you can also open in the tool above and in the Lewis structure and molecule builder lessons, so the picture, the dot structure and the number always agree.

Everything here has a single central atom and no overall charge. That is the honest limit of this model: it will not answer for a polyatomic ion like NH₄⁺ or CO₃²⁻, and it will not answer for a molecule with two or more central atoms, such as ethene (C₂H₄) or ethanol. VSEPR still works on those, but you apply it to each central atom separately, and the chart above tells you what each one does.

Using this with a class

Have students draw the Lewis structure first, count the domains out loud, and predict the shape before checking. Two drills that work: give them the molecule and ask for the class, then give them the class and ask for a molecule. The second is harder, and it is the one the domain-count mode is built for. Compare CH₄, NH₃, and H₂O side by side to watch the angle shrink as lone pairs appear. The widget is free to embed on your own site or LMS using the snippet below.