Lewis Acids and Bases

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Abril Guanes 2A
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Lewis Acids and Bases

Postby Abril Guanes 2A » Mon Nov 16, 2020 10:12 pm

Hello! Can someone help me by writing a general rulebook / guidelines for identifying Lewis acids and bases? I'm struggling with identifying them on the homework and UA sessions. Thank you in advance !

Q Scarborough 1b
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Re: Lewis Acids and Bases

Postby Q Scarborough 1b » Mon Nov 16, 2020 10:19 pm

Hi,

Lewis acids accept electrons whereas Lewis bases donate electrons. Metal cations accept electrons in acid-base reactions. Molecules with an excess of electrons, such as anions or molecules with a lone pair electrons, can donate electrons. Such as H2O

Courtney Situ 2B
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Re: Lewis Acids and Bases

Postby Courtney Situ 2B » Mon Nov 16, 2020 10:21 pm

First off definitions:

Lewis acid: accepts electron pairs
Lewis base: donates electron pairs

The easiest way to tell if an atom is a lewis acid or base is to look at the charge (if it has one). If it is an anion (negative, like S2-), it can probably donate electrons (lewis base). If it is a cation (positive, like Fe3+), it can probably accept electrons (lewis acid).

If that doesn't work, draw the lewis structure and check if any atoms are missing a complete octet of electrons (keep in mind that there are some exceptions like S and P that can accept more electrons than 8). If it is missing some electrons, that means it can accept electrons (making it a lewis acid). For example, draw out BF3 (boron can accept two more electrons, making BF3 a lewis acid).

Also, some molecules can act as both a lewis acid and a lewis base, like H2O. The O in water has lone pairs, so it can donate them in a reaction, making water a lewis base. However, water can also react with ammonia like so :NH3 + H20 <==> NH4+ + OH-. In this instance, water accepted an electron pair from ammonia, making it a lewis acid. These molecules are described as amphoteric.

Hope this helps!

Akriti Ratti 1H
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Re: Lewis Acids and Bases

Postby Akriti Ratti 1H » Mon Nov 16, 2020 10:33 pm

The Lewis acid accepts the lone pair, while the Lewis base donates it.

Jaclyn Dang 3B
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Re: Lewis Acids and Bases

Postby Jaclyn Dang 3B » Mon Nov 16, 2020 10:48 pm

Are lewis acids and bases going to be on this exam?

Abril Guanes 2A
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Re: Lewis Acids and Bases

Postby Abril Guanes 2A » Tue Nov 17, 2020 8:06 am

Jaclyn Dang 3A wrote:Are lewis acids and bases going to be on this exam?


I saw it on the Outline 3 as a guideline. "Identify Lewis acids and bases", so I suppose so.


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