How you calculate atomic mass unit?

Answer 1

• Step 1: Write out the chemical formula of the compound whose atomic mass you want to calculate. The chemical formula provides the number of atoms in one molecule of a compound (i.e. the chemical formula for water is H2O). For example, the chemical formula of phosphate is H3O4P.
• Step 2: Look up the atomic mass for each individual element in the given compound on the periodic table. This number is commonly found just below the letter symbol for the element. For our example, the atomic mass of hydrogen (H) is 1.008 amu per atom, oxygen (O) is 16.00 amu per atom and phosphorous (P) is 30.97 amu per atom.
• Step 3: Multiply the result for every atom in Step 2 by the number of atoms in one molecule of the compound. Phosphate contains three atoms of hydrogen, four atoms of oxygen and one atom of phosphorous in one molecule. So for phosphate the calculations would be as follows; 1.008 amu/atom x 3 hydrogen atoms per molecule = 3.024 amu of hydrogen per molecule, 16.00 amu/atom x 4 oxygen atoms per molecule = 64.00 amu of oxygen per molecule and 30.97 amu/atom x 1 phosphorous atom per molecule = 30.97 amu of phosphorous per molecule.
• Step 4: Add the numbers calculated for each atom in Step 3 together to determine the total amu for one molecule of the compound. So for phosphate the atomic mass is 3.024 + 64.00 + 30.97 = 97.99 amu in one molecule of phosphate.

Answer 2

The Atomic Mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom. It is calculated by taking the weighted average of the masses of all naturally occurring isotopes of an element, based on their abundance in nature. The atomic mass listed on the Periodic Table is a weighted average taking into account the isotopic composition of the element.