What is metal density, how is it determined? Density calculation for osmium

Density is an important physical quantity for any state of aggregation of matter. In this article, we will consider the question that this is the density of metals, give a table of this parameter for chemical elements and talk about the most dense metal on Earth.

What physical characteristics will be discussed?

Density is a value that characterizes the amount of a substance in a known volume. According to this definition, it can be mathematically calculated as follows:

ρ = m / V.

This value is denoted by the Greek letter ρ (po).

Density is a universal characteristic because it can be used to compare different materials. This fact can be used to identify them, which was done by the Greek philosopher Archimedes, according to legend (he was able to establish a fake of the golden crown by measuring the value of ρ for it).

This parameter for a particular material depends on two main factors:

• from the mass of atoms and molecules constituting the substance;
• from the average interatomic and intermolecular distances.

For example, any of the transition metals (gold, iron, vanadium, tungsten) has a higher density than any carbon material, since the mass of the latter is ten times smaller. Another example. Graphite and diamond are two carbon structures. The second is denser, since the interatomic distances in its lattice are smaller.

Metal density

This is the largest group of the periodic table. A metal is any substance that has a high thermal and electrical conductivity, a characteristic luster of a surface when polished, and the ability to plastic deformation.

Such a chemical element has a low electronegativity compared to substances such as nitrogen, oxygen and carbon. This fact leads to the fact that metal atoms form a metal bond with each other in bulk structures. It is an electrical interaction between positively charged ionic bases and negative electron gas.

Metal atoms in space are arranged in the form of an ordered structure called a crystal lattice. There are only three types:

• cubic;
• Bcc (volume-centered cubic);
• GPU (close-packed hexagonal);
• HCC (face-centered cubic).

The density of metals is a physical quantity that depends on the type of crystal lattice. Below is a table of this parameter for all chemical elements in g / cm ³ , which under normal conditions are in the solid state.

From the table it follows that the density of metals is a variable that varies over a wide range. So, the weakest is lithium, which with the same volumes is twice as light as water. The density of the rare metal osmium is the largest in nature. It is 22.59 g / cm ³ .

How to find the value?

The density of metals is a characteristic that can be determined in two fundamentally different ways:

• experimental;
• theoretical.

Experimental methods are as follows:

1. Direct measurements of body weight and volume. The latter is easy to calculate if the geometric parameters of the body are known, and its shape is ideal, for example, a prism, a pyramid, or a ball.
2. Hydrostatic measurements. In this case, special scales are used, invented by Galileo in the 16th century. The principle of their action is quite simple: first, a body of unknown density is weighed in air, and then in a liquid (water). After that, by a simple formula, the desired value is calculated.

As for the theoretical method for determining the density of metals, this is a fairly simple method that requires knowledge of the type of crystal lattice, the interatomic distance in it, and the mass of the atom. Next, we show with the example of osmium how this method is used.

Osmium rare metal density

It is contained in small quantities on our planet. Most often it is found in the form of alloys with iridium and platinum, as well as in the form of oxides. Osmium has a hcp lattice with parameters a = 2.7343 and c = 4.32 angstroms. The mass of one atom is on average m = 190.23 amu

The above numbers are enough to determine ρ. To do this, use the original formula for density and take into account that one hexagonal prism contains six atoms. As a result, we come to the working formula:

ρ = 4 * m / (√3 * a ² * c).

Substituting the figures recorded above and taking into account their dimensions, we arrive at the result: ρ = 22 579 kg / m ³ .

Thus, the density of the rare metal is 22.58 g / cm ³ , which is equal to the experimentally measured tabular value.