Formula Unit:
* Applies to: Ionic compounds (compounds formed by the electrostatic attraction between positively and negatively charged ions).
* Represents: The simplest whole-number ratio of ions in the compound.
* Example: NaCl (Sodium Chloride) - The formula unit indicates one sodium ion (Na+) for every one chloride ion (Cl-).
* Note: Formula units do not represent actual molecules, as ionic compounds exist as a lattice structure of ions.
Molecular Formula:
* Applies to: Covalent compounds (compounds formed by the sharing of electrons between atoms).
* Represents: The actual number of atoms of each element present in a molecule.
* Example: H₂O (Water) - The molecular formula shows that each water molecule contains two hydrogen atoms (H) and one oxygen atom (O).
* Note: Molecular formulas represent actual molecules, which are discrete units with a defined structure.
In Summary:
* Formula units are used for ionic compounds and represent the simplest ratio of ions.
* Molecular formulas are used for covalent compounds and represent the actual number of atoms in a molecule.
Here's a helpful analogy:
Imagine you have a bag of marbles.
* Formula unit: The ratio of red to blue marbles in the bag.
* Molecular formula: A single marble with specific colors and arrangement.
