If we deal with a diatomic element, the determination of its molecular mass is based on the atomic mass of a single atom of that element. Then, using the molecular mass and chemical formula, we can, for example, establish the share of each element in the mass of the whole molecule. To properly determine molecular mass, whether of elements or compounds, we must first know the molecular formula. How do we determine the molecular mass of chemical elements and compounds?

In this case, it is appropriate to use the term ‘molecular mass of an element’. Some chemical elements, such as nitrogen, hydrogen, oxygen, fluorine, bromine, iodine or chlorine, exist in the form of diatomic molecules. The atomic mass of each element may be read out from the periodic table. For this reason, this property can be utilised to identify elements. Importantly, there are no two chemical elements with the same atomic mass. When determining the atomic mass of a single chemical element, we thus have to consider the percentage of isotopes of that element.Ītomic mass is a unique feature of each element. Isotopes are variants of the same chemical element which have a constant atomic number (their nuclei contain the same number of protons) but differ in mass number (have different numbers of neutrons). What is important, most chemical elements that exist on the Earth are mixtures of several isotopes. The mass of chemical elements is normally expressed in atomic mass units (u). To properly determine the molecular mass of a chemical compound, we must first know the atomic mass of the elements it consists of. Therefore, to make the determination of molecular masses easier and avoid having to deal with unwieldy units, they have introduced a new atomic mass unit (u), which is defined as 1/12 of the mass of the carbon isotope nuclide 12C. Absolute atomic masses are extremely low, such as 10 -24g. The molecular masses of elements and chemical compounds are expressed in units (u). The molecular mass of a single molecule of a given chemical compound depends on which and how many atoms it consists of. The molecular mass of a chemical compound is the total of atomic masses of the elements composing the compound.

Periodic table of elements molar masses