VSEPR Theory

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#1
Can someone help me with the VSEPR Theory, I can't seem to remember any of it; the bond angles and names are so confusing.

How do you know how many lone pairs an element has as well?

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3 years ago
#2
(Original post by RoyalSheepy)
Can someone help me with the VSEPR Theory, I can't seem to remember any of it; the bond angles and names are so confusing.

How do you know how many lone pairs an element has as well?

The theory itself (as far as I'm aware) is just based around the fact that there's repulsion between pairs of electrons (be them covalently bonded or as a lone pair) due to the fact that they have the same charge (negative relative charge of -1 or an actual charge of -1.60 x 10-19 C), and also the ideas of which types of electrons repel more i.e lone pair - lone pair repels more than bonding pair - lone pair which repels more than bonding pair - bonding pair.

These varying levels of repulsion are all to do with how close the pairs of electrons are to the central atom = lone pairs are more easily attracted to the central atom, are closer and therefore repel more - likely something to do with where they likely exist (smaller charge cloud).

As for working out the number of bonding pairs / lone pairs, use this following link: http://www.chemguide.co.uk/atoms/bonding/shapes.html
Jim Clark gives the method I personally use and one that is very effective.

Once you can utilise this method to calculate the number of bonding pairs or lone pairs, it is just a matter of associating the appropriate numbers of each with the shape name and bond angle(s) - this is just about memorising.
1
#3
(Original post by Kozmo)
The theory itself (as far as I'm aware) is just based around the fact that there's repulsion between pairs of electrons (be them covalently bonded or as a lone pair) due to the fact that they have the same charge (negative relative charge of -1 or an actual charge of 1.60 x 10-19 C), and also the ideas of which types of electrons repel more i.e lone pair - lone pair repels more than bonding pair - lone pair which repels more than bonding pair - bonding pair.

These varying levels of repulsion are all to do with how close the pairs of electrons are to the central atom = lone pairs are more easily attracted to the central atom, are closer and therefore repel more - likely something to do with where they likely exist (smaller charge cloud).

As for working out the number of bonding pairs / lone pairs, use this following link: http://www.chemguide.co.uk/atoms/bonding/shapes.html
Jim Clark gives the method I personally use and one that is very effective.

Once you can utilise this method to calculate the number of bonding pairs or lone pairs, it is just a matter of associating the appropriate numbers of each with the shape name and bond angle(s) - this is just about memorising.
I'm finally starting to get it after reading your post and the website, I'll just have to keep revising the bond angles and names then, and also use your method for working out the lone pairs.

Thank you very much for your help!
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3 years ago
#4
(Original post by RoyalSheepy)
There isn't much to add from the above poster who answered the question brilliantly. As an A2 student, there isn't much to memorise in chemistry other than a few things. This is one of them. Now you have the opportunity of learning this now at AS so what I'm about to tell you can really help you. It's been scientifically confirmed that spaced repetition is the best way to memorise, so if you use the free app and make flashcards for the angles it will make sure you know the shape, angle and name by heart. This means you can easily gain those easy marks during the exam. Just a friendly tip
1
#5
(Original post by AlphaWolfZ)
There isn't much to add from the above poster who answered the question brilliantly. As an A2 student, there isn't much to memorise in chemistry other than a few things. This is one of them. Now you have the opportunity of learning this now at AS so what I'm about to tell you can really help you. It's been scientifically confirmed that spaced repetition is the best way to memorise, so if you use the free app and make flashcards for the angles it will make sure you know the shape, angle and name by heart. This means you can easily gain those easy marks during the exam. Just a friendly tip
Thank you very much! I'll try making flash cards as you've said, and try to learn them all . Also which app do you recommend for this sort of revision?

Thanks again
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3 years ago
#6
(Original post by RoyalSheepy)
Thank you very much! I'll try making flash cards as you've said, and try to learn them all . Also which app do you recommend for this sort of revision?

Thanks again
Anki is the ultimate pinnacle of flashcard programmes due to it's awesome spaced repetition algorithm. And now I'm not sponsored or anything. In medical school, it's consistently ranked as the number 1 app students used. The best part about is you could take an image of a bond, and blank out details that you'll have to recall. Depending on how hard you found the questions, it will adapt to when to ask you the recall it again. Here is a quick video on the potential of anki. Have fun
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