Shapes Of Molecules. Flashcards
What a lone pairs?
These are pairs of valent electrons that are not being used in bonding.
What are bonding pairs?
These are the pair of electrons shared by two atoms joined in a covalent bond.
What is the V.S.E.P.R principle?
This sums up the reasons for molecular shapes.
Pairs of electrons take up positions around the central atom so that there is minimum repulsion between them.
Lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion.
Why do lone pairs exert a stronger repulsive force than bond pairs?
Because they are only attracted by one nucleus so the electron clous shape is shorter and fatter than a bonding pair of electrons which is held by two nuclei.
How can we predict the shape of any simple molecule?
By applying three rules:
All pairs of electrons contribute to the overall shape of the molecule by taking up positions as far apart as possible around the central atom
Lone pairs of electrons exert a bigger repulsive force than bonding pairs of electrons
Multiple bonds are regarded as consisting of one electron pair only.
What is the shape and angle present for a molecule with a V.S.E.P.R value of 2?
Shape - linear
Bond angle 180°
What is the shape and angle present for a molecule with a V.S.E.P.R value of 3?
Shape - Triganol planar.
Bond angle - 120°
What is the shape and angle present for a molecule with a V.S.E.P.R value of 4?
Shape - tetrahedral
Bond angle - 109.5°
Exceptions. (Due to presence of lone pairs)
NH₃
Shape - pyramidal
Bond angle - 107°
H₂O
Shape - Bent
Bond angle - 104°
What is the shape and angle present for a molecule with a V.S.E.P.R value of 5?
Shape - trigonal bi-pyramidal
Bond angles - 90° and 120°
What is the shape and angle present for a molecule with a V.S.E.P.R value of 6?
Shape - octahedral
Bond angle - 90°