3.2 Determination of formulae

• Empirical formula is the simplest whole number ratio of atoms of each element in a compound
• Molecular formula is the actual number of atoms of each element in a molecule
• Empirical formula can be calculated by dividing the percentage by the atomic number of the element, and comparing the ratios of the atoms
• Molecular formulae can be calculated by dividing the molecular mass by the empirical formula, and multiplying that number by the empirical formula
• A hydrated compound is crystalline and contains water molecules
• An anhydrous compound contains no water molecules
• Water of crystallisation refers to water molecules that are bonded into the crystalline structure of a hydrated compound
• Finding the moles of water in crystallisation is calculated by finding the mass of water and dividing by the molecular mass