1. Count groups, not bonds — a group is one sigma bond or one lone pair.
Multiple bonds count as a single group, so you only ever count from 2 to 4.
2. Four groups means sp3 and tetrahedral geometry.
Every single-bonded carbon fits here, using all four hybrid orbitals for sigma bonds.
3. Three groups means sp2, trigonal planar, with one leftover p orbital forming a pi bond.
Any atom holding one double bond and two other groups lands here.
4. Two groups means sp, linear, with two leftover p orbitals making two pi bonds.
Triple bonds and cumulated double bonds like CO2 give this arrangement.
5. The same count works on heteroatoms — remember to include lone pairs.
Water's oxygen has 2 bonds plus 2 lone pairs, so 4 groups make it sp3.
6. Summary
Count groups = sigma bonds + lone pairs · Multiple bond = 1 group · 4 → sp3 · 3 → sp2 · 2 → sp · Include lone pairs on O and N
Quiz yourself
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sp2 — it has 3 groups: two sigma bonds plus one double bond (counted as one group).
It carries 2 sigma bonds and 2 lone pairs, giving 4 groups. Lone pairs count, so it is sp3.
Two groups — each double bond counts once — so the carbon is sp and linear.
sp — the triple bond is one group and the single bond is another, totaling 2 groups.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.