Atomic Number and Relative Molecular Mass

Atomic Number and Relative Molecular Mass

Atomic Number

Definition

• The atomic number is the number of protons present in the nucleus of an atom.
• It is also equivalent to the number of electrons in a neutral atom where the number of protons equals the number of electrons.

Significance

• The atomic number is unique to each element and is used to identify the element on the periodic table.
• Elements are arranged in order of increasing atomic number on the periodic table.
• The atomic number determines the chemical properties of an element due to its direct relationship with the electron configuration.

Relative Molecular Mass

Concept and Calculation

• The relative molecular mass of a substance is the sum of the relative atomic masses of the atoms in its molecular formula.
• It takes into account the number of each type of atom in the molecule.
• The relative atomic mass of an atom is usually taken from the periodic table and has no units.
• For example, water’s relative molecular mass would be calculated by adding together the relative atomic masses of two hydrogen atoms (1 each) and one oxygen atom (16), resulting in a total of 18.

Significance

• Relative molecular mass is important in determining the ratios of different elements in a compound.
• It also allows for the amount of a substance in a given volume (the concentration) to be calculated if the mass is known.
• Understanding relative molecular mass aids in balancing chemical equations and predicting the outcomes of reactions.

Knowledge of atomic number and relative molecular mass forms a critical basis for understanding more complex chemistry including stoichiometry, reactions, and the behaviours of different elements and compounds.