If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# VSEPR for 4 electron clouds

In this video, we apply VSEPR theory to molecules and ions with four groups or “clouds” of electrons around the central atom. To minimize repulsions, four electron clouds will always adopt a tetrahedral electron geometry. Depending on how many of the clouds are lone pairs, the molecular geometry will be tetrahedral (no lone pairs), trigonal pyramidal (one lone pair), or bent (two lone pairs). Created by Jay.

## Want to join the conversation?

• at it is easy to understand how the unpaired electrons repel the hydrogens attached to nitrogen so that a trigonal pyramidal shape is achieved. But what forces drive the formation of a tetrahedral shape for methane? Why doesn't it assume a flat plane? Wouldn't that create the greatest distance among the hydrogens?
• If it assumed a flat plane, then the angles between the Hs would be 360°/4 = 90°.
A tetrahedral shape allows the angles between the Hs to be 109.5°, greater than the 90° that a flat plane would allow.
• At , how do you know that the lone pairs on oxygen are adjacent to each other, instead of having one above and one below and the hydrogens forming a 180 degree angle with the oxygen?
• In compounds such as Methane, seen drawn at , all of the 4 bonding electron clouds are a 109.5 degrees from each other. Since water also has 4 electron clouds, it will take the same shape, except with unbonding electron clouds taking the place of two of those bonding electron clouds. So the angle between the hydrogen atoms will always be ~109.5 degrees (104.45, to be presice, due to reasons he stated) and the structure will always be bent/angular, you'll just be looking at if from a different angle depending on where the lone pairs were placed.
• Why do lone pair of electrons occupy more space than bond pairs?
• The lone pair of electrons are situated more closer to the central atom than the bonding electron. Hence, they have more repulsion and thus, occupy more space than bond pairs.
• At and two previous other times, how do you calculate the angles between the hydrogens?
• So if the center has electrons that aren't bond to any other atom is also counted as a electron cloud.
• how is trigonal pyramidal different from tetrahedral? A tetrahedron IS a triangular pyramid.
• A tetrahedron is a triangular pyramid but a triangular pyramid is not necessarily a tetrahedron(the regular polygon), so you're right but by using both terms it gives you just that little bit more precision in describing the shapes.
• How do you predict how much the lone pairs of electrons will push the hydrogens in water? Like, how do they know that the Lone pairs reduce the angle from 107º to 104.5º and not to 100º or 105.5º?
(1 vote)
• They can measure the bond angles by techniques like X-ray spectroscopy.
• what is the basic concepT to understand the VSEPR THEORY....??
(1 vote)
• The basic concept is that electrons repel each other and will try to get as far away from each other as possible.
• At , how is it that 109.5 separates all the clouds better on a single plane compared to 90?
• But it isn't on a single plane, it's in 3D space. 109.5 degrees just happens to be the maximum angle when you have 4 equal groups.

If you need proof then Jay did do a mathy video that proves this on here, might be easier just accept it for what it is.
• Bond angles are given at 2;40,, at and at but there is no mention of how they are determined/calculated or their importance to a given molecule's structure. In fact, in over an hour of VSEPR there is no mention whatsoever of why a molecule's shape is important.... does anyone know?
• Molecular shape is used in determining the stability of the molecule and how it can bond with other molecules; this becomes more relevant in the section on hybrid orbitals and hybridization.
• How do we determine the bond angles of the different shapes?
(1 vote)
• First consider the shape you're determining the bond angles of. An easy example is the angle of a trigonal planar shape. All angles are 120 degrees because they only occupy one plane and must add up to 360. Here are some common bond angles, a lot of it is simply memorization.

`1 Axis Shapes` - These form a bond with one other atom and are considered to have "no shape" or bond angle. They are sometimes referred to as linear as well.

`2 Axis Shapes` - These are all linear (they only form bonds with two other atoms), therefore they all have bond angles of 180 degrees. These are "sp" hybridized.

`3 Axis Shapes` - Forming bonds with three different atoms. These are "sp2" hybridized. The different 3 axis shapes are:
Trigonal Planar (120 degrees) [3 single bonds]
Trigonal Planar (120 degrees) [2 single bonds] [1 double bond]
Bent/V-Shaped (104.5 degrees) OR (90<x<120 degrees) [1 lone pair] [1 double, 1 single bond]
No shape [2 lone pairs] [1 double bond]

`4 Axis Shapes` These are "sp3" hybridized.
Tetrahedron (109.5 degrees) OR (90<x<120 degrees) [4 single bonds]
Trigonal Pyramidal (107.5 degrees) OR (90<x<120 degrees) [1 lone pair] [3 single bonds]
Bent/V-Shaped (104.5 degrees) OR (90<x<120 degrees) [2 lone pairs] [2 single bonds]
No shape [3 lone pairs] [1 Single Bond]