# Question #cf35e

Jul 3, 2017

Well, an $\text{atom}$ is a discrete NEUTRAL particle........

#### Explanation:

And of course the $\text{Noble Gases}$ are excellent examples of atoms. Do you agree?

And an ion is a discrete CHARGED particle, cationic or anionic.......of course, for every anion, there must be (somewhere!) a corresponding cation.....(why $\text{must?}$, because as far as we know charge is conserved).

Examples of ions include $N {a}^{+}$ and $C {l}^{-}$.

The difference between a molecular ion and a free radical? Well, a molecular ion is a collection of atoms with a positive or negative charge, e.g. $N {H}_{4}^{+}$ and $C l {O}_{4}^{-}$. And a free radical is an ion or species that contains at least ONE unpaired electron. Hydrogen peroxide (a neutral molecule) is an excellent source of free radicals.....

$H O - O H + \Delta \rightarrow 2 H \dot{O}$

Free radicals tend to be highly reactive species because they tend to pair up, and if they do so with a neutral species, they create another free radical that tends to continue the radical chain. Halogens are an excellent source of free radicals......as witness the reaction of halogen molecule under UV light......

${X}_{2} + h \nu \rightarrow 2 \dot{X}$

And with species such as toluene, that can stabilize free radicals, we can get a radical chain of reactions.......

$\dot{X} + {H}_{3} C P h \rightarrow H - X + {H}_{2} \dot{C} - P h$

And the benzyl radical reacts with UNREACTED halogen........

$P h - \dot{C} {H}_{2} + {X}_{2} \rightarrow P h C {H}_{2} X + \dot{X}$

And thus in the very act of reaction, a new halogen radical is delivered that continues the radical chain of reactions........