Shapes of Molecules Flashcards
What does molecular shape depend on?
Their shape depends on the number of pairs of electrons in the outer shell of the central atom
What do electron pairs exist as?
Charge clouds
How do charge clouds affect the shape of a molecule?
Electrons are negatively charged, so charge cloud will repel each other as much as they can. This means the pairs of electrons in the outer shell of an atom will sit as far apart from each other as they can. This means that lone-pair charge clouds will repel more than bonding-pair charge clouds
What electron pairs give the greatest angles in a molecule?
The greatest angles are between lone pairs of electrons, and bond angles between bonding pairs are often reduced because they are pushed together by lone-pair repulsion
How do you predict the shape of a molecule?
- First work out which is the central atom
- Work out the number of electrons in the outer shell of the central atom
- Divide by 2 to find the number of electron pairs
- Compare the number of electron pairs to the number of bonds to find the number of lone pairs and the number of bonding pairs around the central atom
What shape?
2 electron pairs - no lone pairs
Linear - bond angle = 180’
What shape?
3 electron pairs - no lone pairs
Trigonal planar - bond angle = 120’
What shape?
4 electron pairs - no lone pairs
- Tetrahedral - bond angle = 109.5’
What shape?
5 electron pairs - no lone pairs
- Trigonal bipyramidal - bond angle = 90’ and 120’
What shape?
6 electron pairs - no lone pairs
- Octahedral - bond angle = 90’
What shape?
4 electron pairs - 1 lone pairs
Trigonal pyramidal - bond angle = 107’
What shape?
4 electron pairs - 2 lone pairs
Bent - bond angle = 104.5’
What shape?
5 electron pairs - 1 lone pair
Seesaw - bond angle = 87’ and 102’
What shape?
5 electron pairs - 2 lone pairs
T-shaped - bond angle = 88’
What shape?
6 electron pairs - 2 lone pairs
Square planar - bond angle = 90’
