Since 1961 reference unit of relative atomic and molecular mass accepted 1/12 part of isotope of carbon (called carbon unit). Thus, relative atomic mass is a number which shows how much the absolute mass of atom of any chemical element is more than carbon unit. And the mass of the most carbon unit is equal 1.66*10 in degree of-24 grams. How you can find relative atomic mass?
Instruction
1. The only thing that is required to you - Mendeleyev's Table. In it strictly certain place - "cage" or "cell" is allocated to each element. In any cell there is an information containing such data: the element symbol consisting of one or two letters of the Latin alphabet, the serial (atomic) number corresponding to quantity of protons in an atomic nucleus and size of its positive charge, distribution of electrons on electronic levels and subtotals. Also there is one more very important size – that relative atomic mass specifying how much atom of this element is heavier than reference carbon unit.
2. Consider on a concrete example. Take alkaline metal the sodium which is located in Mendeleyev's Table at number 11. Its relative atomic mass specified there – about 22.99 and. e. m (atomic units of mass). It means that each atom of sodium is heavier than the carbon unit taken for a comparison standard, approximately by 22, 99 times. In round figures it is possible to take this size for 23. Therefore, its weight is equal 23*1.66*10 in degree-24 = 3.818*10 in degree of-23 grams. Or 3.818*10 in degree of-26 kg. You calculated the absolute mass of atom of sodium.
3. But, certainly, to use in calculations such sizes extremely inconveniently. Therefore, as a rule, use relative atomic masses. And relative atomic mass for the same sodium is equal about 22.99 and. e. m.
4. For any element in Mendeleyev's Table his relative atomic mass is specified. If there is a need, it is possible to calculate easily and absolute atomic mass, having increased the size of relative atomic mass by the size of carbon unit (1.66*10 in degree of-24 grams).