[discussedtree]

I'm really confused as none of the definitions of radical on the internet compare to this.

This is from my college textbook of Applied Chemistry-

   

Radicals

    Every inorganic compound is made up of two electrically charged parts called radicals. One part has positive charge and is called basic radical, while the other part has negative charge and is called acid radical. Hence,

    An atom or a group of atoms which forms a part of an inorganic compound is called a radical.

    For example :

    1. Sodium Chloride is made up of two parts:

    (i) Sodium radical (Na⁺) and (ii) Chloride radical (Cl^-)

    The two radicals combine to form sodium chloride molecule.

    2. Copper sulphate is made up of two parts:

    (i) Cupric radical (Cu²⁺) and (ii) Sulphate radical (SO₄^2-)

    The two radicals combine to form copper sulphate molecule.

    It should be noted that a radical cannot exist independently.

This definitely doesn't mean the same as free radicals.

From wikipedia:

   

Historically, the term radical in radical theory was also used for bound parts of the molecule, especially when they remain unchanged in reactions. These are now called functional groups.

I don't think it means "functional group" because how can sodium be a functional group?!. Functional groups are in organic chemistry, right?

Can someone explain what the term "radical" means here?

[Corribus]

A radical in modern usage is an atom, molecule, or other species with a lone (unpaired) electron.

The language that the book uses is admittedly rather confusing. Example: case of sodium chloride. A sodium atom is a radical because it has a single unpaired electron. Likewise for a chlorine atom. When two atoms of Na (radical) and Cl (radical) come together, the chlorine takes an electron from the sodium to form a salt, which is made of a sodium cation (not a radical) and a chlorine anion (not a radical).

So, I disagree with your book calling NaCl made up of the radicals Na⁺ and Cl^-. At best it's confusing the way it's written. I think it'd be more appropriate to say that most inorganic compounds (that are salts) are formed by two radicals coming together to form (formally) ions in which all electrons are paired. As with many things in chemistry, there are most certainly exceptions to this generalization, but it works for the most part.

You'll notice that most elements don't exist in nature (aside from very unusual environments) as lone atoms because they have unpaired electrons and are therefore radicals. Radicals are high energy species that react to form molecules and salts because the pairing of spins generally leads to a more thermodynamically favorable state.  The exceptions are found at low pressures (where reaction probability is low), at very high energies/temperatures (where such high energy species can exist transiently) and noble gasses, which are not radicals and are therefore perfectly happy to float around as lone atoms.

[rwiew]

About this functional group part - I think radical used to mean anything that was a part of a species but could not exist independently (a methyl radical would have meant a methyl 'functional' group, a sodium radical would have been Na+). Just forget about this, you'll just get yourself very confused! How old is this book?

[Babcock_Hall]

I agree with both of rwiew's points.