Formulas, functional groups and naming
Formulas, functional groups and naming
- A hydrocarbon contains only carbon and hydrogen; alkanes are the simplest.
- A functional group is the reactive part that decides a molecule's properties.
- We draw molecules in several ways and name them systematically.
Practice
A functional group is:
Molecules with the same functional group behave alike, because the group is the reactive part.
Types of formula
| Formula | What it shows |
|---|---|
| general | the pattern for a family — alkanes are $\text{C}_n\text{H}_{2n+2}$ |
| molecular | the actual atom counts — $\text{C}_4\text{H}_{10}$ |
| structural | the groups in order — $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_3$ |
| displayed | every atom and bond drawn |
| skeletal | lines for bonds; carbons at corners, H on carbon hidden |
Practice
The general formula of the alkanes is:
Alkanes follow CₙH₂ₙ₊₂ (e.g. C₄H₁₀ for butane).
Practice
In a skeletal formula:
Skeletal formulas use a zigzag of lines; carbon atoms are the corners/ends and their hydrogens are implied.
Naming
- A stem for the carbon count: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6).
- An ending for the functional group, and numbers to show where groups are.
Practice
Which stem is used for a chain of four carbons?
meth=1, eth=2, prop=3, but=4, pent=5, hex=6.
You've got it
Key idea
- a functional group is the reactive part; same group → similar properties
- formulas: general ($\text{C}_n\text{H}_{2n+2}$) / molecular / structural / displayed / skeletal
- name with a stem (meth/eth/prop/but…) + an ending + numbers