To calculate the molecular mass of a compound in atomic mass units (AMU), you need to determine the sum of the atomic masses of all the atoms present in the molecule. Here's a step-by-step process:
Identify the chemical formula of the compound: Determine the symbols and the number of atoms of each element in the compound. For example, let's consider water (H2O).
Obtain the atomic masses: Look up the atomic masses of each element from the periodic table. These values are typically expressed in atomic mass units (AMU).
Multiply the atomic mass by the number of atoms: Multiply the atomic mass of each element by the number of atoms present in the compound. In the case of water (H2O), we have two hydrogen (H) atoms and one oxygen (O) atom.
Atomic mass of hydrogen (H) = 1.008 AMU Atomic mass of oxygen (O) = 15.999 AMU
Molecular mass of water (H2O) = (2 * atomic mass of hydrogen) + atomic mass of oxygen = (2 * 1.008 AMU) + 15.999 AMU = 2.016 AMU + 15.999 AMU = 18.015 AMU
Therefore, the molecular mass of water (H2O) is 18.015 AMU.
If there are multiple elements in the compound, sum up all the calculated values from step 3 to obtain the molecular mass in AMU.
It's important to note that atomic masses are average values based on the isotopic composition of the element. The periodic table provides these average atomic masses.