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Same as the question, I looked up radicals etc, and could see that methyl radical or phenyl radical had 1 extra electron that would have been a bonding electron normally. However it is not considered a negatively charged compound. Why is it so? Also do positive free radicals exist? How stable are they?

amspsingh04
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    "Extra electron" of radicals is misleading expression . It is not extra in sense giving negative net charge, but rather extra as an odd electron, not paired with another is a lone electron pair or in a chemical bond. Radical ions exist too, like superoxide anion $\ce{^{.}O2^{-}}$. E.g. a hydrogen atom is a radical, It stops being a radical with no electron as a proton, or with 2 electrons as a hydride anion. – Poutnik Nov 15 '22 at 18:59

2 Answers2

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Imagine a neutral molecule. Cut the molecule in half along any single bond. Each piece gets one electron from that bond. Now each half has a single unpair electron, but each piece is also still neutral based on the charge of the original molecule by conservation of charge. Most radicals that we look at fall into this category.

However, you can also have cationic radicals or anionic radicals, where the species with the unpaired electron is respectively positive or negative.

A good example of this is when a sodium-ammonia (Birch) reduction of benzene. The benzene molecule picks up an extra electron, which must be unpaired since all of the other electrons are paired. But since we added an electron, the radical must also be anionic.

Zhe
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The formal charge of a species is defined as:

$$C=G-N-B$$

Where:

$C$ is the charge of the species.

$G$ is the group number the species belongs to.

$N$ is the total number of non-bonded electrons the species has.

$B$ is the total number of bonds the species has with other atoms.

For example, the formal charge of the carbon atom in a methyl radical would be:

$$C=4-1-3=0$$

A chlorine radical would also be electrically neutral:

$$C=7-7-0=0$$

As would a hydrogen radical:

$$C=1-1-0=0$$

As others have pointed out, there are some cases where the radical can also be negative, like the superoxide radical.

The charge of the oxygen atom that carries the free radical is:

$$C=6-5-1=0$$

While the charge of the other oxygen atom is:

$$C=6-6-1=-1$$

Which gives a net charge of $-1$.

Sam202
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