Science 2023 What is the density of metals, how is it determined? Density calculation for osmium

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

## What physical characteristic are we talking about?

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.

Designate this value with the Greek letter ρ (ro).

Density is a universal characteristic because it can be used to compare different materials. This fact can be used to identify them, which is what the Greek philosopher Archimedes did, according to legend (he was able to establish a fake 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 the atoms and molecules that make up the substance;
• from 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 atom is ten times less. Another example. Graphite and diamond are two carbon structures. The second is denser, since the interatomic distances in its lattice are smaller.

## Density of metals

This is the largest group in Mendeleev's periodic table. A metal is any substance that has a high thermal and electrical conductivity, a characteristic surface luster when it is polished, and the ability to undergo 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 in bulk structures form a metallic bond with each other. It is an electrical interaction between positively charged ionic bases and a negative electron gas.

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

• cubic;
• BCC (body centered cubic);
• HCP (hexagonal close-packed);
• FCC (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 / cm3, which under normal conditions are insolid state. From the table it follows that the density of metals is a value that varies over a wide range. So, the weakest is lithium, which, with the same volumes, is two times lighter than water. The density of the rare metal osmium is the highest in nature. It is 22.59g/cm3.

## How do you find the value?

The density of metals is a characteristic that can be defined 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 operation is quite simple: first, a body of unknown density is weighed in air, and then in a liquid (water). After that, the required value is calculated using a simple formula.

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, using the example of osmium, we will show how this method is used.

## Density of the rare metal osmium Hefound in trace amounts 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 an hcp lattice with parameters a=2.7343 and c=4.32 angstroms. The average mass of one atom is m=190.23 amu

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

ρ=4m/(√3a2c).

Substituting the figures written above and taking into account their dimensions, we arrive at the result: ρ=22 579 kg/m3. Thus, the density of a rare metal is 22.58 g/cm3, which is equal to the experimentally measured table value.