The Valence covering Electron Pair Repulsion (VSEPR) Theory can be provided to guess the shapes of molecules based on the number of electron pairs roughly the central atom.

You are watching: In the vsepr theory what is repelling what

Therefore we must be familiar with drawing dot-and-cross diagrams for an easy molecules first before we can apply VSEPR theory correctly.

1. Basic Shape

As electron pairs are negatively charged and also will repel every other, the electron pairs about the central atom will take on a form that will minimise repulsion between them.

So based on the total variety of electron pairs, there room a few distinct basic shapes and also bond angle that we require memorise.

2 electron bag - linear3 electron pairs - trigonal planar4 electron pairs - tetrahedral5 electron bag - trigonal bipyramidal6 electron bag - octahedral

VSEPR simple shape

2. Actual Shape

The actual shape relies on the number of link pairs and also lone pairs around the main atom.

In VSEPR Theory, single bond, double bond and also triple bond are all treated as one bond pair each.

When we name the form of an really molecule, we do not take it the lone pair right into consideration yet the lone pair still exerts a repulsion and affects the form of the molecule.

Also, the repulsion involving a lone pair is better than repulsion entailing a link pair, therefore the existence of a lone pair will decrease the bond angles as it will certainly squeeze the bond pairs closer together.

An calculation that is useful to determine the bond edge without memorising is for every lone pair, the link angle will certainly decrease by 2 degree.

2 electron pairs

2 bond bag + 0 lone pair = linearVSEPR actual form 2 electron pairs

3 electron pairs

3 bond bag + 0 lone pair = trigonal planar2 bond pairs + 1 lone pair = bentVSEPR actual shape 3 electron pairs

4 electron pairs

4 bond pairs + 0 lone pair = tetrahedral3 bond pairs + 1 lone pair = trigonal pyramidal2 bond pairs + 2 lone pairs = bentVSEPR actual shape 4 electron pairs

5 electron pairs

5 bond pairs + 0 lone pair = trigonal bipyramidal4 bond bag + 1 lone pair = see-saw3 bond pairs + 2 lone bag = T-shape2 bond bag + 3 lone bag = linearVSEPR actual shape 5 electron pairs

6 electron pairs

6 bond bag + 0 lone pair = octahedral5 bond pairs + 1 lone pair = square pyramidal4 bond bag + 2 lone pairs = square planar3 bond pairs + 3 lone pairs = T-shape2 bond bag + 4 lone pairs = linearVSEPR actual form 6 electron pairs

For the in-depth step-by-step discussion on exactly how to identify shapes that molecules using VSEPR Theory, check out this video!

Topic: chemical Bonding, physical Chemistry, A Level Chemistry, Singapore

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