HONC 1234 Rule
Advanced Chemistry 2013 – 2014
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There are many patterns in the way atoms in compounds are connected. We use the
HONC 1234 rule to construct structural formulas from molecular formulas.
HONC 1234 Rule
Hydrogen
H
Oxygen
O
Nitrogen
N
Carbon
C
1 – hydrogen atoms form 1 bond
2 – oxygen atoms form 2 bonds
3 – nitrogen atoms form 3 bonds
4 – carbon atoms form 4 bonds
Steps to drawing a structural formula:
1. Connect the carbon atoms
2. Insert the nitrogen or oxygen atoms, either on the ends or somewhere in the
middle of the carbon chain.
3. Add the hydrogen atoms to follow the HONC 1234 rule.
4. Check that the structure follows the HONC 1234 rule!
Sometimes there is more than one possibility for a structural formula from a
molecular formula; these molecules are called isomers.
1) See if you can draw in 2 isomers for each molecular formula below.
Molecular
Formula
C3H8
C2H6O
C3H9N
Structural Formula #1
Structural Formula #2
Smells Lab Pre-Activity Question
2) There are at least two structural isomers of C2H4O2, one of which is shown below. Draw
the other isomer and predict the smell of each using the experimental data in the table
below.