Chemical Formula vs. Empirical Formula

Definition: A chemical formula is a symbolic representation of a chemical compound, indicating the types of atoms present and the exact number of each type in a molecule or ionic compound.
Purpose: Its primary purpose is to clearly and concisely show the elemental composition of a substance.
Information Conveyed:
- Elements Present: The chemical symbols identify the elements (e.g., H for Hydrogen, O for Oxygen, C for Carbon).
- Number of Atoms: Subscripts indicate the number of atoms of each element in a molecule. If no subscript is present, it is understood to be one atom.
- Molecular Structure (Implied): For molecular compounds, it describes the composition of a single molecule. For ionic compounds, it represents the simplest ratio of ions in the crystalline lattice.
Examples:
- Water (H_{2}O): Indicates a molecule contains 2 hydrogen atoms and 1 oxygen atom.
- Carbon Dioxide (CO_{2}): Shows one carbon atom and two oxygen atoms.
- Glucose (C{6}H{12}O_{6}): Represents a molecule with 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
- Sodium Chloride (NaCl): Denotes a formula unit with one sodium ion and one chloride ion in an ionic lattice.

Definition: An empirical formula represents the simplest whole-number ratio of atoms of each element present in a compound.
Purpose: It provides the most reduced form of the elemental composition, often derived from experimental data (e.g., combustion analysis or elemental analysis).
Relation to Chemical (Molecular) Formula:
- The empirical formula can be identical to the chemical (molecular) formula if the ratio of atoms is already in its simplest whole-number form.
- Alternatively, the chemical formula can be a whole-number multiple of the empirical formula.
How to Determine: To find the empirical formula from a molecular formula, divide all subscripts by their greatest common divisor.
Examples:
- Water (H_{2}O):
  - Molecular Formula: H_{2}O
  - Greatest Common Divisor (GCD) of 2 and 1 is 1.
  - Empirical Formula: H_{2}O (In this case, the empirical and molecular formulas are the same).
- Glucose (C{6}H{12}O_{6}):
  - Molecular Formula: C{6}H{12}O_{6}
  - GCD of 6, 12, and 6 is 6.
  - Empirical Formula: (C{6/6}H{12/6}O{6/6}) = CH{2}O
- Hydrogen Peroxide (H{2}O{2}):
  - Molecular Formula: H{2}O{2}
  - GCD of 2 and 2 is 2.
  - Empirical Formula: (H{2/2}O{2/2}) = HO
- Butane (C{4}H{10}):
  - Molecular Formula: C{4}H{10}
  - GCD of 4 and 10 is 2.
  - Empirical Formula: (C{4/2}H{10/2}) = C{2}H{5}

Chemical Formula (Molecular Formula): Gives the actual number of atoms of each element in a molecule.
Empirical Formula: Gives the simplest whole-number ratio of atoms of each element in a compound. It is often the first step in determining the full molecular formula of an unknown compound from experimental data.