What Shape Does HCN Have?

HCN has a Linear molecular geometry (AX2, linear) with a bond angle of 180°. The central carbon carries 2 bonding domain(s) and 0 lone pair(s) — 2 electron domains in total. The carbon has exactly two electron domains, so the h–c–n axis stays straight.

Hybridisation is conventionally described as sp at carbon. Polarity: Strongly polar — the C–H and C≡N dipoles do not cancel.

1. Molecular Identity and Key Parameters

Molar mass is the average value rounded for procurement use. Hybridisation labels are the conventional VSEPR-level description; orbital treatment becomes more nuanced at higher levels of theory.

2. Drawing the Lewis Structure of HCN, Step by Step

1. Count valence electrons: 1 (H) + 4 (C) + 5 (N) = 10 — a total of 10 electrons (5 pairs) must be placed.
2. Build the skeleton: place the carbon at the centre and attach the terminal atoms with single bonds; hydrogen is never a central atom. Each single bond consumes 2 electrons.
3. Complete terminal octets: distribute the remaining electrons as lone pairs on the terminal atoms first (hydrogens already carry their duet from the single bond).
4. Satisfy the central atom: H–C≡N: one C–H single bond plus a C≡N triple bond; nitrogen keeps one lone pair.
5. Verify: Carbon is complete via the triple bond; nitrogen is complete with one lone pair. Apply the standard formal-charge check (valence − nonbonding − half of bonding electrons) to confirm the drawn form.

A worked diagram of this molecule is kept in the companion guide: HCN Lewis structure.

3. VSEPR Analysis: Why HCN Is linear

VSEPR theory counts electron domains — every σ bond counts once regardless of bond order, and every lone pair counts once. HCN has 2 such domains around the carbon: 2 bonding and 0 lone. 2 domains correspond to a linear electron-domain arrangement; with no lone pair to hide the observed molecular shape is linear (AX2).

Bond angle: 180° because the carbon has exactly two electron domains, so the H–C–N axis stays straight.

Polarity: Strongly polar — the C–H and C≡N dipoles do not cancel.

4. The Most Common Mistake When Drawing HCN

5. Why the Geometry Matters in Practice

Adiponitrile (nylon chain) and methyl methacrylate manufacture; anhydrous and aqueous specifications differ sharply and are not interchangeable in a purchase order.

Structure-level identity is exactly what a purchase order has to fix: the same molecular formula can hide isomers, hydrates or salt forms with different handling profiles. Before ordering, match CAS (74-90-8), assay, water content and container rating against the datasheet, and request the COA batch that will ship.

Compare Hydrogen Cyanide (HCN) supply offers →

6. Quick FAQs on HCN

7. References

1. IUPAC / Gillespie, Assessment of the VSEPR model. Basis of AXE notation and lone-pair ordering. VSEPR entry
2. PubChem compound record for Hydrogen Cyanide (HCN). Registry number, formula and computed descriptors. PubChem 74-90-8
3. Companion Lewis-structure guide on this site. Worked diagram for HCN. Lewis structure HCN