What it does
Why is water bent but carbon dioxide straight? Why is ammonia a pyramid? VSEPR (valence shell electron pair repulsion) answers it with one idea: the electron pairs around a central atom push each other as far apart as they can. This page lets you add bonded atoms and lone pairs with big + and − buttons and see the 3D shape at once. Drag the picture to turn it; the orange arc marks a bond angle.
It follows the Class 11 Chemistry chapter on chemical bonding and molecular structure (VSEPR theory and hybridisation), and it is a good way to picture the carbon compounds of Class 10 too. For the full symmetry of a shape, go on to the point group; to turn real molecules from a file, use the molecule viewer.
How to use it
- Pick a Molecule from the list (NH₃ is first), or press + and − under Bonded atoms and Lone pairs to make your own AXₙEₘ.
- Read the shape name, the arrangement of the electron pairs, the ideal bond angle and the hybridisation under the picture.
- Untick Show lone pairs to see only the atoms: that is what the shape name describes.
- In Count the pairs from a formula, choose a central atom, the outer atom, how many there are and the charge. The tool counts the electrons left on the central atom, step by step, and Show this shape above draws it.
- In Check yourself, choose the shape of four molecules or ions and press Check for the worked answers.
Worked example: ammonia, NH₃
Nitrogen has 5 valence electrons. Three single bonds to hydrogen use 3 of them, so 2 are left: one lone pair. Electron pairs = bonded atoms + lone pairs = 3 + 1 = 4, so the pairs point to the corners of a tetrahedron and nitrogen is sp³. The atoms make a trigonal pyramidal shape. The lone pair pushes harder than the bonds, so the bond angle is less than 109.5° (measured about 107°). Press − on Bonded atoms and + on Lone pairs and you get water: 2 + 2 = 4 pairs, still sp³, now bent.
Shapes at a glance
| Pairs | Lone pairs | Shape | Ideal angle | Hybrid |
|---|---|---|---|---|
| 2 | 0 | linear | 180° | sp |
| 3 | 0, 1 | trigonal planar, bent | 120° | sp² |
| 4 | 0, 1, 2 | tetrahedral, pyramidal, bent | 109.5° | sp³ |
| 5 | 0, 1, 2, 3 | trigonal bipyramidal, see-saw, T-shaped, linear | 90°, 120° | sp³d |
| 6 | 0, 1, 2 | octahedral, square pyramidal, square planar | 90° | sp³d² |
Tips
- Multiple bonds count once. In CO₂ each C=O double bond is one “pair direction”, so carbon has 2, and CO₂ is linear.
- Lone pairs in a trigonal bipyramid go round the middle (equatorial), where they have fewer close neighbours. That is why SF₄ is a see-saw and XeF₂ is linear.
- Polar or not? If all the outer atoms are the same and the shape is symmetric (linear, trigonal planar, tetrahedral, square planar, octahedral), the bond dipoles cancel.
FAQ
Why does the counter treat O as using 2 electrons? Oxygen usually forms a double bond to the central atom, so the central atom spends 2 electrons on it. Hydrogen and the halogens use 1, nitrogen 3.
What happens with an odd number of electrons, like NO₂? The single leftover electron still takes up space, so it counts as a domain; the molecule is a radical.
Is this an official NCERT tool? No. It is a free fibub page written to help with these chapters. Your choices stay on your device.
Where the numbers come from
- VSEPR rules (pairs spread as far apart as possible; lone pair repulsion greater than bond pair repulsion; lone pairs equatorial in a trigonal bipyramid) and the shape names are general chemistry, written fresh for fibub.
- Ideal angles worked out from the geometry of each arrangement (tetrahedral angle = arccos(−1/3) ≈ 109.47°). The measured angles for NH₃ (about 107°), H₂O (about 104.5°) and SO₂ (about 119°) are the rounded values quoted in general chemistry teaching.
- Checked: all 18 example molecules and 52 practice species give the shapes in the standard VSEPR table (AX₂ to AX₆ with up to 3 lone pairs).
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
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Last updated 2026-11-09.