Organic and inorganic compounds:
Similarities:::---
1) In both organic and inorganic compound, the elements joining in making compound complete their octet.
2) Organic compound shows isomerism (R/S , E/Z , cis/trans, enantiomers, diastereomers, etc), just as inorganic compound do (Δ/Λ, enantiomers, R/S enantiomers, cis/trans, fac/mer isomers, etc).
3) Organic compound and inorganic compounds can be very active in chemical reactions, e.g. organolithium reagents could be flammable or even pyrophoric (generally stored under 10°C), while inorganic reagents like in this paper are quite rapid...
Differences:::---
1) Organic compound are very long in size so they can make polymer but inorganic compound are not very long but its structure might me complex.
2) The boiling,melting point of organic compound is lass than inorganic compound.
3) Organic compound always contains carbon but inorganic compounds might not.
4) Organic compound
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Ion and Radical Atoms:
In some sense they are a bit similar. The main difference is that a neutral radical has no charge imbalance between the protons and electrons, but the cation or anion does.
Ions are written with an explicit charge because of that charge imbalance, but radicals may or may not have an imbalance of charge. Just because a molecule is a radical doesn't mean it's neutral.
For example, if you shoot 2-pentanone with an electron beam for Electron "Impact" Mass Spectroscopy, where you essentially study molecules whose structures break into smaller pieces as a result of interacting with stray electrons to identify the molecules, you get a cationic radical (middle, or far right of the following diagram).