Shapes Of Molecules And Ions Flashcards
What is electron pair repulsion theory?
A model used in chemistry for explaining and predicting the shapes of molecules. Electrons have a negative charge so electron pairs repel each other. Applies to ions too
Why is electron repulsion theory useful?
The electron pairs surround a central atom determine the shape of the molecule or ion
The electron pairs repel one another so they are arranged as far as possible from each other, minimises repulsion and hold bonded atoms in a definite shape.
Different numbers of electron pairs give different shapes.
How to draw in 3D
Solid line, bond on plane
Wedge, bond out of plane
Dashed line, bond into plane
Compare the strengths between bonded pairs and lone pairs in terms of repulsion
2 bonded pairs are less repulsive than 2 lone pairs.
What is the bond angle?
The angle between the bonded pairs of electrons
What is the rule for bond angles
The bond angle is reduced from 109.5 minus 2.5 for every lone pair in molecules with 4 electron shapes.
What shape do you get?
4 bonded pairs/regions
0 lone pairs
Tetrahedral
109.5
What shape do you get?
3 bonded pairs/regions
1 lone pairs
Pyramidal
107
What shape do you get?
2 bonded pairs/regions
2 lone pairs
Non linear
104.5
What shape do you get?
2 bonded pairs/regions
0 lone pairs
Linear
180
What shape do you get?
3 bonded pairs/region
0 lone pairs
Trigonal planar
120
What shape do you get?
6 bonded pairs/regions
0 lone pairs
Octahedral
90
