Shapes of Molecules
Some of the images are available in Chime, which lets the viewer see them in 3D and allows manipulation.
In molecules there are 2 types of electron
1. Bonding Pairs
2. Non-bonding or lone pairs
The combinations of these determine the shape of the molecule
The standard example is ammonia (NH3) [Chime View]
Predict the shapes and bond angles in molecules and ions by using the Electron-Pair Repulsion Theory for up to 4 electron pairs (including lone pairs).
The board specifies these as examples:
The board specifies that you are able to predict the shapes of molecules analogous to these
These are the simplest shapes, involving only 2 bonding pairs
The simplest is BeCl2[Chime View]
Carbon dioxide (CO2) is another example. It has bonding pairs which all repell equally.
Other examples include:
The standard example is water, the unique properties of water are closely linked to its shape.
1) Only 3 atoms so must be linear
2) Bond angle is 104.5°
3) Shape impact on water’s strange behaviour
Any molecule with 2 bonding pairs and 2 lone pairs will have a crooked shape, giving a bond angle significantly less than the angle on a tetrahedral structure
[Chime Version] of water here
Other examples include H2S and SO2.
3 bonding pairs and 1 lone pair = Trigonal pyramidal.
[Chime View] here
Notice the bond angle of 107°.
Other examples include PH3 (phosphine) and SO32- (sulphite)
4 bonding pairs all with equal bonds gives a tetrahedral structure with a bond angle of 109.5° in methane.
[Chime View] of Methane
Other examples include NH4+, SO42-, PO43-, Ni(CO)4.
These contain 3 – bonding pairs and no non-bonding pairs.
Boron trifluoride is an example of this (BF3). Bond angle of 120°.
[Chime Version] here
Examples include BF3, SO3, NO3-, CO32-, C2H4.
Questions – see handwritten sheet.