(Polar molecules, Non-polar molecules, etc.)
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I believe we should know the bond angles of the molecular shapes we go over during lecture (i.e. Linear-180 degrees & Tetrahedral-109.5 degrees). We predict bond angles when there are lone pairs on the central atom, which influence the molecular shape and affect the bond angle. For example, we can predict that the sulfite ion (the central atom has 1 lone pair and 3 bonding pairs) will have a bond angle of slightly less than 109.5 degrees since the 4 pairs are arranged tetrahedrally around the central atom to reduce repulsion.
Maya Pakulski 3D wrote:So we basically just have to memorize which bond angles go with which shapes?
Yes that's honestly the easiest way, but conceptually you should know that the reason the bond angles occur is due to repulsion between lone pairs and bonding pairs.
It's probably easiest to just memorize a chart with all the bond angles stated, but for the test he said we just have to be able to say that a trigonal pyramidal shape has a smaller bond angle than a tetrahedral because of the lone pair having more repulsion than the bonded pair.
if you can remember the bond angles of the basic molecular geometries containing no lone pairs (i.e. linear=180, trigonal planar=120, tetrahedral=109.5, trigonal bipyramidal=120, 90, & 180, and octahedral= 90) then you can predict that the bond angles with be slightly less than these numbers when lone pairs are added because of the higher repulsion of lone pairs.
The angles for the molecular shapes are all standardized. When a molecule is polar, the bond angles will change, but we do not need to know the exact values. All we need to indicate is that the angles either decrease or increase (i.e. with lone pairs of electrons instead of bonding pairs).
RRahimtoola1G wrote:It's probably easiest to just memorize a chart with all the bond angles stated, but for the test he said we just have to be able to say that a trigonal pyramidal shape has a smaller bond angle than a tetrahedral because of the lone pair having more repulsion than the bonded pair.
but for this we don't have to know the bond angle exactly, just that it is less than and why?
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