Definition of Atomic Weight

In everyday life when we talk about weight and mass, we understand that the greater the mass of something, the greater the weight. However, in the realm of physics both concepts have different meanings. In fact, if someone moves from the Earth to the Moon, his mass will not change, but his weight will, since the force exerted by the Moon on us is less than the force exerted by the Earth.

In the context of chemistry, the concepts of weight and mass acquire another meaning

To measure the atomic mass A unit of measurement is used that is a very small fraction of a gram and for this the reference of carbon 12 is used to calculate the mass of all the elements.

Atomic weight is measured in units of atomic mass, although it is not the mass of a single atom or of a molecule. On the contrary, it is the average weight that exists between the proportion of elements that can be found on Earth. In this way, the mass of all the isotopes of the chemical element and divide by the number of isotopes. For this

reason the concept of atomic weight is equivalent to another: relative atomic mass.

If we take potassium as a reference, in the periodic table appears with an atomic number that expresses the number of protons in the nucleus (this number is the 19), while at the bottom the potassium has the number 39.0983 to indicate its weight atomic. This means that on average potassium isotopes have a mass of 39.0983 grams per mole.

Observe that the mole is a unit of measurement that allows us to better understand the quantities of atoms and molecules of the different elements (the number used to express the moles is known as the number of Avogadro).

On the other hand, the molecular weight is obtained by adding the atomic weights of the atoms in a molecule. In potassium sulfate (K2SO4) the molecular weight includes the atomic weight of each atom and, at the same time, the number of atoms of each of the elements in the molecule.

Stoichiometry is the branch of chemistry that allows calculations related to the different elements of nature

Is discipline It informs us about the amount of material that is needed for a given product to have optimal conditions. Thus, the numerical relationships between grams, moles and elementary particles are established in a chemical reaction.

Photo Fotolia: EvgeniyBobrov

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