In everyday life when talking about weight and mass, we understand that the greater the mass, the greater the weight of something. However, in the field of physics, both concepts have different meanings. In fact, when an individual moves from Earth to the Moon, its mass does not change, but its weight does, since the force exerted by the Moon on us is less than the force exerted by the Earth. Atomic Weight
In the context of chemistry, the concepts of weight and mass take on another meaning
To measure atomic mass, a unit of measurement is used that is a very small fraction of a gram, for which the carbon 12 reference is used to calculate the mass of all elements.
Atomic weight is measured in units of atomic mass, although it is not the mass of a single atom or molecule. Rather, it is the average weight that exists among the proportion of elements that can be found on Earth. In this way, the mass of all isotopes of the chemical element is added together and divided by the amount of isotopes. For this reason, the concept of atomic weight is equivalent to another: relative atomic mass.
If we take potassium as a reference, it appears in the periodic table with an atomic number that expresses the number of protons in the nucleus (this number is 19), while at the bottom potassium has the number 39,0983 to indicate its atomic weight. This means that on average potassium isotopes have a mass of 39.0983 grams per mol. Atomic Weight
It is worth noting that the mole is a unit of measurement that allows us to better understand the amounts of atoms and molecules of different elements (the number used to express the moles is known as Avogadro’s number).
On the other hand, molecular weight is obtained by adding the atomic weights of the atoms in a molecule. In potassium sulphate (K2SO4), the molecular weight includes the atomic weight of each atom and, at the same time, the number of atoms of each element in the molecule.
This course informs us about the amount of material needed for a given product to be in optimal condition. Thus, the numerical relationships between grams, moles and elementary particles in a chemical reaction are established .