# Chemistry: Shapes of Molecules, easy way to remember the names?

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#1
eg. trigonal planar
trigonal bipyramidal
octahedral etc.

It's impossible to learn them! how do you remember them, mnemonics, pictures, song/rhyming ?

will give rep to the person with the best idea, thanks.
0
9 years ago
#2
(Original post by Osman1993)
eg. trigonal planar
trigonal bipyramidal
octahedral etc.

It's impossible to learn them! how do you remember them, mnemonics, pictures, song/rhyming ?

will give rep to the person with the best idea, thanks.
Why not just learn what the words mean?

Planar = flat, i.e all atoms in the same plane.

Trigonal = tri + gonal - three cornered = a triangle

Trigonal planar = flat triangle
---------------------------------------------------------------------------

Trigonal pyramidal = a three cornered pyramid (everyone knows what a pyramid looks like!)

Trigonal bipyramidal - two trigonal pyramids joined at the base

---------------------------------------------------------------------------

Tetrahedral = four faced = tetra + hedra = four + faces

---------------------------------------------------------------------------

Octahedral = eight faced = octa + hedra = eight + faces

This is not so obvious as it looks like a cube. But a cube could also be thought of as two four sided pyramids (square base) joined base to base
1
9 years ago
#3
(Original post by Osman1993)
eg. trigonal planar
trigonal bipyramidal
octahedral etc.

It's impossible to learn them! how do you remember them, mnemonics, pictures, song/rhyming ?

will give rep to the person with the best idea, thanks.
I made a ridiculous mnemonic last year for this but it worked for me! haha, mnemonics being stupid help you remember them

"Large turtles play tennis to break oranges"

Large = Linear (2 bonding pairs)
-------------------------
Turtles = Trigonal (3 bonding pairs)
Play Planar
------------------------
Tennis = Tetrahedral (4 bonding pairs)
------------------------
To = Trigonal (5 bonding pairs)
Break Bipyrimidal
------------------------
Oranges = Octahedral (6 bonding pairs)

I'm aware this doesn't cover stuff like trigonal pyrimidal (when you have lone pairs on the shape) but this mnemonic helps with the general structure and you can work it out from there
Hope this helps.
2
9 years ago
#4
(Original post by Osman1993)
eg. trigonal planar
trigonal bipyramidal
octahedral etc.

It's impossible to learn them! how do you remember them, mnemonics, pictures, song/rhyming ?

will give rep to the person with the best idea, thanks.
El Mayonnaise!

Most of them are shape related eg trigonal planar has three bits coming off of it and is flat (hence planar). Linear.. it's a line Non linear - not a line. Tetrahedral's just one you know because most things you'll have to write about are based on it anyway. Trigonal bipyramidal has 2 pyramids with triangular bases, joined together.

If you draw an octahedral molecule, you'll see that there are 8 faces on it - hence 'octa'

Mr Myers (yes, he still teaches me ) did a funky dance to explain them. He'd just got a new laptop and was really excited. Mad man. He still hates Adam.

And I typed this at school, hopefully it won't have screenshotted at the last bit, eh?
0
9 years ago
#5
O for the days when we all had classical educations

Made all this kind of thing much easier because everyone knew what tri- and penta- meant!

(Original post by Navi_Fairy)

I think that's harder to memorise than the shapes!
3
9 years ago
#6
Person above gets the ratings.
0
9 years ago
#7
(Original post by Plato's Trousers)
O for the days when we all had classical educations

Made all this kind of thing much easier because everyone knew what tri- and penta- meant!
I

I think that's harder to memorise than the shapes!
Never had problems remembering those :s Its easier if you visualise the shape (or even look them up ina book)
0
9 years ago
#8
I assume you're doing the same chemistry I did, in which case there aren't that many to learn.

Linear
Angular (2 bonds + lone pair)
Trigonal Planar (3 bonds)
Pyramidal (3 bonds + lone pair)
Tetrahedral (4 bonds)
Trigonal Bipyramidal (5 bonds)
Octahedral (6 bonds)

The best way in my opinion is just to learn what the name means.

Linear and angular are fairly obvious, a line, and an angle.
Trigonal Planar - Tri means 3 so there are 3 bonds, planar means in one plane, so it is a flat shape with 3 equally space bonds.
Pyramidal, this shape is caused by a lone pair such as in ammonia, and it is literally pyramid shaped, easy.
Tetrahedral - tetra means four, and this is the only shape with 4 bonds I imagine you would need to learn.
Trigonal bipyramidal - Imagine the trigonal planar shape, however this one has 5 bonds, one above and one below, this effectively makes two pyramids. Trigonal bipyramidal.
Octahedral can be quite confusing as oct- means eight, but this has 6 bonds. You can either just learn this one, or imagine all the atoms to be joined making a 3d shape with eight faces (two four sides pyramids stuck together)

There are some weird ones, like umbrella and T-shaped, but I doubt you would be expected to really know these, if you do see a shape you don't recognise they are often named as the shape suggests (an umbrella shaped molecule looks like an umbrella).

You can try mnemonics and rhymes, but I personally don't find them helpful, more often than not I get confused about the actual mnemonic itself. I think if you have a good understanding of what the names mean it really helps.

As for bond angles - you just have to learn these! Good luck with your chemistry.
0
3 years ago
#9
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