# Help with shapes of molecules

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#1
How am I supposed to remember all the shape names and the bond angles and be able to draw them. Anyone have an easy method of learning them all? 😩
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1 year ago
#2
Honestly I struggle so much with this as well. I just memorised a grid of coordinate number vs number of lone pairs and drew it on the back of my exam paper last time and then reference it throughout but something else might work better for you
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1 year ago
#3
(Original post by raeesahh)
How am I supposed to remember all the shape names and the bond angles and be able to draw them. Anyone have an easy method of learning them all? 😩
The names are kinda intuitive once you know they're based on the shape that atoms take around a central atom. Here's my tip for remembering the shapes that have 4 electron pairs (btw I use "surrounding atoms" and "bonding pair of electrons" synonymously):
• Tetrahedral — 4 atoms (bonding pairs of electrons) surround a central atom and those 4 atoms are arranged in a tetrahedral shape. You're just gonna have to remember that the angle is 109.5°.
• Trigonal pyramidal — Replace one of those atoms above with a lone pair of electrons. Now there are 3 atoms surrounding a central atom. Lone electron pairs repel stronger than bonding electron pairs, so the angle between the bonding electron pairs decreases. Each lone pair decreases the angle by 2.5°. There's one here, so the angle is 107°. You draw this shape the same as tetrahedral, except one of the surrounding atoms is now a lone pair of electrons. The 4 total atoms should look like a pyramid.
• Bent/non-linear — Replace another bonding pair with a lone pair. There are 2 lone pairs now, therefore the angle is 109.5 - (2 x 2.5) = 104.5°. The shape is like a water molecule and should hopefully be self-explanatory.

Maybe look at the 3D shapes that the names are based on to understand the shape and angles better
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1 year ago
#4
And by memorising the grid I mean draw and write it out 50billion times
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1 year ago
#5
https://chemrevise.files.wordpress.c...onding-aqa.pdf

search around chemrevise + other sites....
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1 year ago
#6

This is the table I made if it helps (I do OCR) I'd definitely say see if you can use some molymods to see the 3D structures of the shapes, it helps a lot! Like you see that trigonal planar is a 2D triangle hence 'trigonal' and 'planar'. I've also made flashcards that say like '2BP 2LP' on one side then the shape on the other side, and go over these regularly. I forgot them very quickly so regular reviewing of them is important for me at least!
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#7
Thank you so much for all the help!! Definitely got a better idea now 😄
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1 year ago
#8
(Original post by raeesahh)
all the shape names and the bond angles
Which spec do you do?
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#9
(Original post by Pigster)
Which spec do you do?
AQA
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1 year ago
#10
(Original post by raeesahh)
AQA
Shame AQA have loads to remember. Learn the shapes for 2, 3, 4, 5 & 6 bond pairs and 0 lone pairs. Then, when you change bp to lp, the shapes basically are still the same, it is just that the bp get squeezed closer together. AQA don't really mind if you place the lp on the equator or at the poles, so don't worry about 3bp, 2lp being T-shaped or trig. plannar (its T, BTW).
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1 year ago
#11
I made a mnemonic which is as follows:
Large - Linear. 2BP. 180°
Turtles play -Trigonal planar. 3BP. 120°
Tennis - Tetrahedral. 4BP. 109.5°
Ping-pong - Pyramidal (Trigonal). 3BP+1LP. 107°
Archery - Angular/Non-linear/Bent 2BP+2LP. 104.5°
To break - Trigonal Bipyramidal. 5BP. 90/120°
Oranges. - Octahedral. 6BP. 90°
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#12
(Original post by nia(the_devoted))
I made a mnemonic which is as follows:
Large - Linear. 2BP. 180°
Turtles play -Trigonal planar. 3BP. 120°
Tennis - Tetrahedral. 4BP. 109.5°
Ping-pong - Pyramidal (Trigonal). 3BP+1LP. 107°
Archery - Angular/Non-linear/Bent 2BP+2LP. 104.5°
To break - Trigonal Bipyramidal. 5BP. 90/120°
Oranges. - Octahedral. 6BP. 90°
Thank you!! Much appreciated 😄
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1 year ago
#13
When it comes to memorising things, make a poster and put it up somewhere you'll see it everyday. Every time you go past it, test yourself, read the information out loud etc. Flashcards are my biggest help for memory as well. It's good to do paper flashcards as well as using something like quizlet. You can get the quizlet app on your phone and go over the sets when you get free time throughout the day like when you're on the bus to or from school or something. For me, the only way I really memorise is to repeatedly test myself and it eventually goes into my head. Hope that helps
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#14
(Original post by azelia)
When it comes to memorising things, make a poster and put it up somewhere you'll see it everyday. Every time you go past it, test yourself, read the information out loud etc. Flashcards are my biggest help for memory as well. It's good to do paper flashcards as well as using something like quizlet. You can get the quizlet app on your phone and go over the sets when you get free time throughout the day like when you're on the bus to or from school or something. For me, the only way I really memorise is to repeatedly test myself and it eventually goes into my head. Hope that helps
Thanksss! I’ll defo download the quizlet app and make better use of my time 😁
1
1 year ago
#15
(Original post by raeesahh)
Thanksss! I’ll defo download the quizlet app and make better use of my time 😁
Try this "shapes of molecules test" a few times.

p/w: guest
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