Definition

Noun: A symbolic representation of a molecule that shows the exact number and type of atoms of each element present. It is derived from empirical formula data and the known molecular weight of the compound.

Usage

The molecular formula is used in chemistry to specify the precise composition of a single molecule of a substance. It is distinct from an empirical formula, which only shows the simplest whole-number ratio of elements.

Examples

• The molecular formula for water is H₂O, indicating two hydrogen atoms and one oxygen atom per molecule.
• Glucose has the molecular formula C₆H₁₂O₆.
• While both benzene (C₆H₆) and acetylene (C₂H₂) share the same empirical formula (CH), their different molecular formulas reveal they are distinct compounds.

Advanced Usage

• Determination: A molecular formula is often determined by combining the empirical formula with experimental data on the compound's molecular mass. For example, if the empirical formula is CH₂O and the molecular mass is 180 g/mol, the molecular formula is C₆H₁₂O₆ (as 180 / 30 = 6).
• Isomers: Different compounds, known as isomers, can share the same molecular formula but have different structural arrangements. For instance, C₂H₆O is the molecular formula for both dimethyl ether and ethanol.

Variants and Related Words

• Empirical Formula (n): A formula giving the simplest whole-number ratio of atoms of each element in a compound (e.g., CH₂O for glucose).
• Structural Formula (n): A formula that shows not only the number and type of atoms but also the arrangement of atoms within the molecule.
• Chemical Formula (n): A general term for any expression that shows the elements in a compound and their relative proportions.

Synonyms

• Chemical formula (in the specific context of defining a single molecule's exact composition).

Related Phrases/Concepts

• Molecular Weight: The sum of the atomic weights of all atoms in a molecule, crucial for determining the molecular formula from an empirical formula.
• Percent Composition: The percentage by mass of each element in a compound, which can be used to derive the empirical and then the molecular formula.

Noun

1. a chemical formula based on analysis and molecular weight