(40) GCSE Chemistry Revision "Relative Atomic Mass"
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9 Terms
Relative Atomic Mass
A weighted average of the mass numbers of an element's isotopes based on their abundance.
Isotopes
Atoms of the same element with different numbers of neutrons.
Abundance
How common each isotope is in a sample.
Chlorine Isotopes
Chlorine has isotopes with mass numbers of 35 and 37, with 35 being more abundant.
Calculation of Relative Atomic Mass
(mass number of isotope one x percent abundance of isotope one + mass number of isotope two x percent abundance of isotope two) / 100.
Example of Boron's Isotopes
Boron has two isotopes: mass number 10 with 20% abundance, and mass number 11 with 80% abundance.
Relative Atomic Mass of Boron
Calculated to be 10.8, rounded to 11 in the periodic table.
Magnesium Isotopes
Magnesium has three isotopes: mass number 24 (79% abundance), 25 (10% abundance), and 26 (11% abundance).
Relative Atomic Mass of Magnesium
Calculated to be 24.3, rounded to 24 in the periodic table.
