GCSE Chemistry (AQA)

196 videos | 19 hours

Atomic structure and the periodic table A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes

Molecular Formulae

6:06 Atoms, Elements and Compounds
Spec 4.1.1.1 4.3.1.1.
Previous Compounds Next Chemical Reactions
  • Molecules can be represented using symbols from the periodic table, known as molecular formulas.
  • Diatomic elements naturally exist as pairs of atoms, e.g., O2 for oxygen.
  • Compounds can be formed from different elements, e.g., MgO for magnesium oxide.
  • To write a compound's formula, combine the symbols of its constituent elements.
  • Example: Sodium (Na) and chlorine (Cl) form NaCl.
  • Subscripts indicate the number of atoms in a molecule, e.g., H2O for water.
  • Correct placement of subscripts is crucial in exams to avoid losing marks.
  • Compound names often hint at their composition, e.g., carbon monoxide (CO) and carbon dioxide (CO2).
  • Naming conventions can indicate the number of atoms, e.g., "mono" for one, "di" for two.
  • Calcium carbonate (CaCO3) and sodium hydroxide (NaOH) are examples of compounds with specific naming rules.
  • Some compounds have unique names, e.g., H2O is water, NH3 is ammonia.
  • Understanding these naming conventions is important for recognizing and writing molecular formulas.

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