Group the following as linear and non-linear molecules : H2O, HOCl, BeCl2, Cl2O

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Q. Group the following as linear and non-linear molecules : H2O, HOCl, BeCl2, Cl2O

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Concept understanding — VSEPR Theory

VSEPR Theory: Why Molecules Have the Shapes They Do

Imagine you're in a crowded room. Everyone wants their personal space. If you're standing with a few friends, you'll naturally spread out so no one is too close to anyone else. That's exactly what happens inside a molecule.

The Core Intuition

Electron pairs are negatively charged. They repel each other. In a molecule, the electron pairs around a central atom will arrange themselves as far apart as possible — just like those people in the room. This simple idea is the entire foundation of VSEPR (pronounced "ves-per") Theory.

Note

VSEPR stands for Valence Shell Electron Pair Repulsion. The name tells you exactly what it's about: the repulsion between electron pairs in the valence shell.

The Precise Statement

VSEPR Theory states that the geometry around a central atom is determined by minimizing the repulsion between all electron pairs (both bonding and lone pairs) in its valence shell.

Two key points to hold onto:

All electron pairs repel — whether they are shared (bonding pairs) or unshared (lone pairs).
Lone pairs repel more strongly than bonding pairs. A lone pair is "fatter" — it's only attracted to one nucleus, so it spreads out more and pushes harder on its neighbours.

How to Predict Shape in 3 Steps

Step 1: Count the total electron pairs around the central atom.

Add the number of atoms bonded to the central atom plus the number of lone pairs on it. This gives you the steric number.

Step 2: Arrange those pairs as far apart as possible.

This gives you the electron-pair geometry — the shape if you pretend all pairs are identical.

Step 3: Replace lone pairs with "invisible" space.

The actual molecular geometry is the shape formed by the atoms alone, ignoring lone pairs.

The Common Geometries at a Glance

Steric Number	Electron-Pair Geometry	Lone Pairs	Molecular Geometry	Example	Bond Angle
2	Linear	0	Linear	$\text{CO}_2$	180°
3	Trigonal planar	0	Trigonal planar	$\text{BF}_3$	120°
3	Trigonal planar	1	Bent	$\text{SO}_2$	~119°
4	Tetrahedral	0	Tetrahedral	$\text{CH}_4$	109.5°
4	Tetrahedral	1	Trigonal pyramidal	$\text{NH}_3$	~107°
4	Tetrahedral	2	Bent	$\text{H}_2\text{O}$	~104.5°
5	Trigonal bipyramidal	0	Trigonal bipyramidal	$\text{PCl}_5$	90°, 120°
6	Octahedral	0	Octahedral	$\text{SF}_6$	90°

Watch out

A common mistake: thinking that $\text{NH}_3$ is tetrahedral. It has tetrahedral electron-pair geometry, but because one position is a lone pair, the molecular shape is trigonal pyramidal. The bond angle is 107°, not 109.5°.

Why Lone Pairs Squeeze Bond Angles

Take water ( $\text{H}_2\text{O}$ ). The central oxygen has 4 electron pairs: 2 bonding (to H atoms) and 2 lone pairs. The ideal tetrahedral angle is 109.5°. But the two lone pairs push harder on the bonding pairs, compressing the H–O–H angle to about 104.5°.

In ammonia ( $\text{NH}_3$ ), there's only one lone pair, so the compression is less — the H–N–H angle is about 107°. …

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VSEPR theory predicts molecular shape from electron-pair repulsion. Linear molecules have a bond angle of $180^\circ$ ; non-linear molecules have bent or angular shapes. Linear: BeCl₂; Non-linear: H₂O, HOCl, Cl₂O.

The key to classifying a molecule as linear or non-linear lies in its central atom’s electron-pair geometry. VSEPR (Valence Shell Electron Pair Repulsion) theory tells us that electron pairs — whether bonding or lone — arrange themselves as far apart as possible to minimise repulsion. The shape you actually see (the molecular geometry) depends only on the positions of the atoms, ignoring lone pairs.

Let’s examine each molecule one by one.

H₂O (Water)

Oxygen is the central atom. It has 6 valence electrons; two are used in single bonds with hydrogen, leaving two lone pairs. That gives 4 electron domains around oxygen — a tetrahedral electron-pair geometry. The molecular geometry, however, is bent (or V-shaped) because the two lone pairs push the hydrogen atoms closer together. The bond angle is about $104.5^\circ$ , not $180^\circ$ . So water is non-linear.
HOCl (Hypochlorous acid)

Here oxygen is again central, bonded to H and Cl. Oxygen has 6 valence electrons; it uses two for the O–H and O–Cl bonds, leaving two lone pairs. That’s again 4 electron domains — tetrahedral electron-pair geometry — and the molecular geometry is bent. The H–O–Cl angle is roughly $103^\circ$ . So HOCl is non-linear.
BeCl₂ (Beryllium chloride)

Beryllium is the central atom. It has only 2 valence electrons, both used in single bonds with two chlorine atoms. There are no lone pairs on Be. That gives exactly 2 electron domains, which arrange linearly with a bond angle of $180^\circ$ . The molecular geometry is linear. So BeCl₂ is linear.
Cl₂O (Dichlorine monoxide) …

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Q.Group the following as linear and non-linear molecules : H2O, HOCl, BeCl2, Cl2O

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Q.Group the following as linear and non-linear molecules :
H2O, HOCl, BeCl2, Cl2O

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