Calculate the relative atomic mass for an element.
Understanding Isotopes
Isotopes: Atoms of the same element with different numbers of neutrons.
Example: Isotopes of Chlorine
Both isotopes have an atomic number of 17 (17 protons).
Differ in mass number due to different numbers of neutrons.
Chlorine Isotopes: Mass numbers 35 (18 neutrons) and 37 (20 neutrons).
Relative Atomic Mass
Definition: The weighted average of the mass numbers of an element's isotopes.
Weighted Average: Accounts for the abundance (how common) of each isotope.
Example: Chlorine
Mass number on periodic table is 35.5.
Isotope with mass 35 is three times more abundant than the one with mass 37.
Calculating Relative Atomic Mass
Formula:
[ \text{Relative Atomic Mass} = \frac{(\text{Mass Number of Isotope 1} \times \text{Percent Abundance of Isotope 1}) + (\text{Mass Number of Isotope 2} \times \text{Percent Abundance of Isotope 2})}{100} ]
Example Calculations
Boron
Isotope 1: Mass number 10, Abundance 20%
Isotope 2: Mass number 11, Abundance 80%
Relative Atomic Mass = 10.8 (rounded to 11 in GCSE table)
Magnesium
Isotope 1: Mass number 24, Abundance 79%
Isotope 2: Mass number 25, Abundance 10%
Isotope 3: Mass number 26, Abundance 11%
Relative Atomic Mass = 24.3 (rounded to 24 in GCSE table)
Study Resources
Practice questions available in the vision workbook (link provided in video).