The relative atomic mass was calculated by the efforts of several scientists

Each substance is not something solid, it consists of small particles, which are molecules. Molecules from atoms. From here we can draw conclusions that the determined mass of matter can characterize the molecules and atoms of the incoming elements. At one time Lomonosov devoted most of his work to this topic. However, many curious naturalists have always been interested in the question: "In what units is the mass of a molecule expressed, the mass of an atom?"

But, for starters, we'll dip a bit into history

In the past, in calculations per unit mass of the atom, the mass of hydrogen (H) was always taken. And, proceeding from this, we made all the necessary calculations. However, most compounds are present in nature in the form of oxygen compounds, so the mass of the element atom was calculated with respect to oxygen (O). Which is rather inconvenient, since it was necessary in the calculations to constantly take into account the ratio O: H, equal to 16: 1. In addition, studies showed an inaccuracy in the ratio, it actually was 15.88: 1 or 16: 1.008. Such changes have caused a recalculation of the mass of atoms for many elements. It was decided to leave the value of mass 16 for O, and for H - 1.008. The further development of science led to the discovery of the nature of oxygen itself. It turned out that the oxygen molecule has several isotopes with masses of 18, 16, 17. For physics, it is not acceptable to use a unit having an average value. Thus, two scales of atomic weights were created: in chemistry and physics. Only in 1961, scientists came to the conclusion that it is necessary to create a single scale, which is used today as the "carbon unit." As a result, the relative atomic mass of an element is the mass of an atom in carbon units.

Methods of calculation

The mass of a molecule of any substance consists of the masses of atoms that form a given molecule. Hence, the conclusion is that the mass of the molecule should be expressed in carbon units, as well as the mass of the atom, i.e. The relative atomic mass is determined taking into account the relative molecular weight. As is known, with the help of Avogadro's Law, it is possible to determine the number of atoms in a molecule. Knowing the number of atoms and the mass of the molecule, you can calculate the atomic mass. There are several other ways to define it. In 1858, Cannizzaro proposed a method by which the relative atomic mass is determined for those elements that are capable of forming gaseous compounds. However, this ability is not possessed by metals. Therefore, to determine their atomic mass, a method was chosen that uses the dependence of the atomic mass and heat capacity of the corresponding substance. But all the methods considered give only approximate values of atomic masses.

How was the exact mass of the atoms of the element calculated?

As shown by scientific studies, from these approximate values can determine the exact. To do this, you only need to compare this value with the equivalent. The equivalent of an element is the ratio of the relative atomic mass of the element to its valence in the compound. From this relation the correct relative atomic mass of each element was determined.