Carbon commonly forms four covalent bonds and can connect to other carbon atoms to make chains, branches and rings. These connected carbon frameworks are called carbon skeletons.

A carbon skeleton may contain only single bonds or may include carbon-carbon double and triple bonds. A molecule with only single carbon-carbon bonds is saturated with respect to carbon-carbon bonding; one containing a C=C or C≡C bond is unsaturated.

Organic structures are often drawn with skeletal or line-angle formulas. These drawings suppress most carbon and hydrogen symbols so that connectivity is easier to see.

The conventions are:

• every unlabeled line end is a carbon atom;
• every unlabeled corner where lines meet is a carbon atom;
• a line represents a bond, with two or three parallel lines representing double or triple bonds;
• hydrogens attached to carbon are omitted and inferred so that each neutral carbon has its usual valence of four;
• atoms other than carbon and hydrogens attached to them are normally written explicitly.

An atom such as O, N, S or a halogen embedded in or attached to an organic skeleton is often called a heteroatom.

For example, the line-angle chain

/\/\

contains five carbon atoms: two ends and three internal vertices. If all bonds are single and there are no other substituents, the terminal carbons are CH3 groups and the internal carbons are CH2 groups.

A branch is drawn simply as another line leaving a carbon. A ring is drawn as a closed polygon; a hexagon with no labels therefore represents a six-carbon ring.

When multiple bonds are present, the implied hydrogen count changes. In a carbon-carbon double bond, each carbon already uses two bond orders toward the other carbon, leaving fewer bonds available for hydrogen or substituents.

Reading an explicit example

The condensed formula

$$\mathrm{CH_3CH_2CH(CH_3)CH_2OH}$$

contains five carbon atoms in its skeleton. Its main four-carbon path carries a CH3 branch, and the terminal OH must be written explicitly because oxygen is a heteroatom.

Skeletal notation is not a different molecule model from a Lewis structure. It is a compressed representation that preserves atomic connectivity and bond multiplicities while omitting predictable carbon-bound hydrogens. Lone pairs and formal charges are added explicitly whenever they matter for bonding or reactivity.