Carbon and Its Hybridisation States

Organic chemistry is really the chemistry of one element: carbon. Get carbon right and the rest of the subject stops fighting you. So let's start where the toppers start — with the atom itself.

This is the first lesson in the GOC (General Organic Chemistry) series. GOC is worth up to three questions in JEE, and it sets the foundation for all of organic. Worth doing well.

Why carbon is special

One word: catenation. Carbon bonds to other carbons, over and over, building long chains and rings — think of it as carbon's talent for making friends with its own kind. That single trick is why millions of carbon compounds exist.

Three facts to keep:

• Carbon has 6 protons, 6 neutrons, 6 electrons. (Yes, 666. No wonder organic scares people.)
• It needs 4 electrons to fill its octet, so it forms 4 bonds. Always four.
• Those bonds can be single, double, or triple.

Single, double, triple — and sigma vs pi

A bond is a line. One line is a single bond, two lines a double, three a triple.

Now the rule JEE loves to test:

• Every single bond is one sigma (σ) bond.
• Two atoms share only one sigma bond. Every extra line is a pi (π) bond.

So a single bond is $1\sigma$. A double bond is $1\sigma + 1\pi$. A triple bond is $1\sigma + 2\pi$. Burn that line into memory — you'll use it constantly.

The three hybrid states

Carbon comes in three flavours: sp³, sp², and sp. You don't need orbital theory to spot them. You just count bonds.

sp³ — only single bonds. Four sigma bonds, no pi. Shape: tetrahedral. Methane is the classic:

sp² — one double bond. The carbon goes flat and triangular. That's the ethene you saw above.

sp — one triple bond (or two double bonds). The carbon goes linear — a straight line right through it. That's ethyne.

Here's the whole skill in one move. Look at a carbon, find its highest bond:

• a triple bond → sp
• a double bond → sp²
• only single bonds → sp³

Your turn. In propene, $CH_2{=}CH{-}CH_3$, name each carbon.

Check: the two carbons in the double bond are sp²; the $CH_3$ carbon has only single bonds, so it's sp³.

The four lines to remember

• Carbon forms 4 bonds — always.
• single $= 1\sigma$ · double $= 1\sigma{+}1\pi$ · triple $= 1\sigma{+}2\pi$.
• Count the highest bond: triple → sp, double → sp², single-only → sp³.
• Of the three, sp carbon is the most reactive and most acidic.

Learn to spot hybridisation on sight. Next, we'll use it to predict shape and bond angles — where these states start earning you marks.