Foundations · B02
What molecular formulas and structures can tell us
C₂H₆O can describe more than one substance. That small fact explains why a formula alone is not a complete molecular address.
Counting is useful
A molecular formula states how many atoms of each element occur in one molecule. Ethanol has formula C₂H₆O: two carbon atoms, six hydrogen atoms, and one oxygen atom.
Formulae are compact and make composition easy to compare. They do not, by themselves, state which atoms are neighbors.
Connections change behavior
Ethanol and dimethyl ether both have C₂H₆O, but their atoms connect differently. Ethanol has an O–H group; dimethyl ether has oxygen between two carbons. Their boiling points and reactivity differ.
A structural formula draws or encodes these connections. Bond lines and element symbols give a useful map of a molecule.
One more layer: shape
Some molecules share both formula and connections but differ in three-dimensional arrangement. Those stereoisomers can interact differently with light, living systems, or other molecules.
It is good practice to ask what a representation contains and what it leaves out: atom counts, connections, charge, three-dimensional shape, or experimental conditions.