Chemsitry- Relative Mass- foundational learning

Relative atomic mass

The relative atomic mass, Ar, Is the average mass of an atom of an element on a scale where an atom of carbon 12 is exactly 12. The relative atomic mass of each element is shown in the periodic table

Relative isotopic mass

Relative isotopic mass is the mass of an atom of an isotope that an element on a scale where an atom of carbon 12 is exactly 12

Calculating relative atomic mass

Relative isotopic mass is usually a whole number. Relative atomic mass is an average so it’s not usually a whole number

Relative atomic mass = isotopic masses x percentages

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Total percentage

Relative molecular mass

The relative molecular mass, Mr, Is the average mass of a molecule on a scale where an atom of carbon 12 is exactly 12. To find the Mr, just add up the relative atomic mass values of all the atoms in the molecule .

relative formula mass

Relative formula mass is the average mass of a formula unit on a scale where an atom of carbon 12 is exactly 12. It is used for compounds that are ionic (Or giant covalent such as SiO2). to find the relative formula mass just add up the relative atomic masses (Ar), of all the ions in the formula unit

Calculating the relative formula mass example

The formula unit of CaF2 contains one Ca 2+ ion and two F- ions mix

Mr of CaF2 = 40.1 + ( 2 × 19.0)= 78.1