VSEPR Flashcards
What is VSEPR used for?
Predicting the geometry of main group compounds with attached ligands
What can VSEPR not be used for?
Transition metals
What is the first step of VSEPR?
Decide on the connectivity of the molecule
Which atom is always the central one?
the least electronegative one
What is the second step of VSEPR?
Draw a lewis structure for the molecule and ignore the lone pairs
What is the third step of VSEPR?
Count the electrons in pairs in the valence shell of the central atom
How do we count the electrons in the valence shell of the central atom?
- Count its own valence shell electrons (the group number)
- Add one electron for every atom that is σ bonded to the central atom
- Add or subtract the appropriate number of electrons corresponding to any charge
- Account for any multiple bonds
What is the 4th step of VSEPR?
Put all the electron pairs as far apart as possible using the vertices of the possible shapes
What are the characteristics of linear shape?
2 pairs
2 directions 180 degrees
What are the characteristics of trigonal planar?
3 pairs
3 angles at 120 degrees
What are the characteristics of tetrahedral?
4 pairs
4 directions at 109.5 degrees
What are the characteristics of trigonal bipyramidal?
5 pairs
Angles 90, 120 and 180 degrees between directions
What are the characteristics of octahedral?
6 pairs
Angles of 90 and 120 degrees
What are the characteristics of pentagonal bipyramidal?
7 pairs
Angles of 72, 90 and 180 degrees
Why do multiple bonds repel more than single bonds?
They contain more electrons
What is the order of repulsions?
LP-LP > LP-BP > BP-BP
Why do lone pairs need more space than bonding pairs?
The attractive electrostatic force is weaker and the electron density can expand
What position do multiple bonds and lone pairs occupy in the case of 5 pairs and why?
Equatorial
Equatorial positions have more space than axial
How are the bonds and lone pairs arranged in octahedral?
Two lone pairs or multiple bonds are placed trans to each other
How many BP and LP does linear have?
2 BP
0 LP
How many BP and LP does trigonal planar have?
3 BP
0 LP
How many BP and LP does bent/angular have?
2 BP
1 LP
How many BP and LP does Tetrahedral have?
4 BP
0 LP
How many BP and LP does Pyramidal have?
3 BP
1 LP
How many BP and LP does bent have?
2 BP
2 LP
How many BP and LP does tbp have?
5 BP
0 LP
How many BP and LP does psuedo-tbp have?
4 BP
1 LP
How many BP and LP does T-shaped have?
3 BP
2 LP
How many BP and LP does linear with 5 electron pairs have?
2 BP
3 LP
How many BP and LP does octahedral have?
6 BP
0 LP
How many BP and LP does square pyramidal have?
5 BP
1 LP
How many BP and LP does square planar have?
4 BP
2 LP
What four things need to be considered when adjusting angles from their ideal values to their actual?
- Lone pairs
- Multiple bonds
- Differences in electronegativity
- Differences in size
What do you do for each atom considered to be double bonded to the central atom?
Subtract 1 electron
What do you do for each atom considered to be triply bonded to the central atom?
Subtract 2