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We compare the mass of atoms using the ______ atomic mass unit. This is defined as one ______ of the mass of an _______ of ______-12. Relative atomic mass (Ar) is the ______ average mass of atoms in a given ______ of an element compared to the value of the unified atomic mass unit.

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The number of atoms in exactly 12 ____________ of the isotope carbon-12 is called the ____________ constant. Its value is 6.02 × 10^23 mol−1. So there are 6.02 × 1023 atoms of carbon in 12 g of the carbon-12 ____________. A ____________ is the amount of substance which contains 6.02 × 10^23 specified particles (atoms, molecules, ions or electrons).

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Relative molecular mass (Mr) is the weighted _________ mass of a molecule compared to the value of the unified atomic mass ____________. Relative molecular mass is found by ____________ together the relative atomic ____________ of all the atoms in the molecule. For ionic compounds we use the term relative ____________ mass.

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