What is a molar atom

Atoms and molecules

From atom to molecule

According to Dalton, every substance consists of extremely small particles, which, like Democritus, he called atoms. Individual atoms are very rare in nature, because mostly different or identical atoms combine to form an association, which in chemistry is called a molecule. For example, a molecule of the gas oxygen is made up of two oxygen atoms. Methane is a component of natural gas and always consists of four hydrogen atoms and one carbon atom, i.e. five atoms.


Size and mass of atoms and molecules

Atoms differ in size and mass, both of which are inconceivably small. The Diameter of an atom is only a few nanometers (nm). 1 nm = 10-9 m = 0.000 000 001 m. The is correspondingly low Mass of an atom. For example, a hydrogen atom has mass
0.000 000 000 000 000 000 001 673 mg = 1.673 10-21 mg.



Such numbers can no longer be imagined. Even small amounts of substance consist of an unimaginable number of atoms. The Mass of a molecule results from the sum of the masses of the atoms present in the molecule. If the atomic and molecular masses were given in grams or milligrams, simple calculations would make the daily work of chemists more difficult. Therefore, a very small unit of mass has been created, which is called the atomic unit of mass u. 1 u is the twelfth part of the mass of a carbon atom.

Specifying the mass in u has the advantage that the hydrogen atom, which is the lightest atom, has a mass of 1 u very precisely and the masses of all other atoms can thus be compared with one another. For example, a sulfur atom with a mass of 32 u is twice as heavy as an oxygen atom. In addition, it is very easy to calculate with such numbers.



The Numerical valuefor an atomic mass in the unit u is called relative atomic massand the Numerical value for a molecular mass in the unit u relative molecular weight. Relative relative atomic or molecular masses can be used to compare the masses of different atoms or molecules with one another, which is what matters in chemistry in everyday work. The values ​​can be found in atomic mass tables.


The mole

In everyday life, certain portions of the substance are usually given in grams or in their quantity (number of pieces). There are different units of mass and different units of measure, such as pieces, dozen (12 pieces), bulk (144 pieces) or kilograms, grams or carats (= 0.200 g)

In chemistry, too, substance portions can be specified either in units of mass (e.g. g or u) or in units of quantity. A practical unit of the amount of substance is the mole (abbreviation: mol), with which chemists can work very practically. One mole is the number of particles contained in 12 grams of carbon. This number could be determined using various methods. It amounts to 6,023 · 1023 Particle.



So 1 mole of iron consists of 6.023 · 1023 Iron particles, as well as e.g. 1 mol of hydrogen or 1 mol of oxygen from also 6.023 · 1023 There are hydrogen or oxygen particles.

Sometimes one wonders whether there is a connection between the unit of measure "mole" and the unit of mass "gram". For carbon, for example, 12 g of carbon is made up of 6.023 · 1023 Particles exist. But what is the mass of 1 mol of iron or 1 mol of oxygen? Here an atomic mass table is used, from which one can read off that the mass of a hydrogen atom is 1 u, a carbon atom 12 u and an iron atom 56 u.

Thus there are just as many particles in 100 u of hydrogen as in 1200 u of carbon or 5600 u of iron, namely 100 pieces. From this one can conclude that there are exactly as many particles in 1 g of hydrogen or in 56 g of iron as in 12 g of carbon, namely exactly 6.023 x 1023 Particles are located.

In the daily work in chemistry, these considerations have proven to be very helpful, because in order to get the 1 mole of an element or a compound, one does not have to count the atoms, but carry out a weighing. So 1 mol of iron corresponds to 56 g of iron. The mass of 1 mol of a substance is called molar mass or molar mass.