Metals are chemical elements that make up most of the periodic table of D. I. Mendeleev. In this article, we consider their important physical property, such as density, and also give a table of the density of metals in kg / m3.
Substance density
Before we understand the density of metals in kg / m3, we will get acquainted with the physical quantity itself. Density is the ratio of body mass m to its volume V in space, which can be mathematically written as follows:
ρ = m / V
The studied value is usually denoted by the letter of the Greek alphabet ρ (po).
If different parts of the body have different masses, then using the written formula you can determine the average density. In this case, the local density can differ significantly from the average.
As can be seen from the formula, the value of ρ is expressed in kg / m 3 in the SI system. It characterizes the amount of substance that is placed in a unit of its volume. This characteristic in many cases is the hallmark of substances. So, for different metals, the density in kg / m3 is different, which allows them to be identified.
Metals and their density
Metallic materials are solids at room temperature and atmospheric pressure (the only exception is mercury). They have high ductility, electrical and thermal conductivity and have a characteristic luster in the polished state of the surface. Many of the properties of metals are associated with the presence of an ordered crystal lattice, at the nodes of which there are positive ionic cores, connected to each other by a negative electron gas.
As for the density of metals, it varies widely. So, alkali light metals such as lithium, potassium or sodium are the least dense. For example, the density of lithium is 534 kg / m 3 , which is almost two times less than the same value for water. This means that plates of lithium, potassium and sodium will not sink in water. On the other hand, transition metals such as rhenium, osmium, iridium, platinum and gold have a huge density, which is 20 or more times ρ of water.
The table below shows the density of metals. All values correspond to room temperature in g / cm 3 . If these values are multiplied by 1,000, then we get ρ in kg / m 3 .
Why are metals with high density and low value exist? The fact is that the ρ value for each particular case is determined by two main factors:
- A feature of the crystal lattice of metal. If this lattice will contain atoms in the most dense packing, then its macroscopic density will be higher. The fcc and hcp lattices have the densest packaging.
- The physical properties of a metal atom. The larger its mass and the smaller the radius, the higher the ρ value. This factor explains why metals with a high density are chemical elements with a large number in the periodic table.
Experimental determination of density
Suppose we have a piece of unknown metal. How can its density be determined? Recalling the formula for ρ, we come to the answer to the question asked. To determine the density of the metal, it is enough to weigh it on any scale and measure the volume. Then the first value should be divided into the second, not forgetting to use the correct units.
If the geometric shape of the body is complex, then its volume will not be easy to measure. In such cases, you can use the law of Archimedes, since the volume of the displaced fluid during immersion of the body will be exactly equal to the measured volume.
The method of hydrostatic weights invented by Galileo at the end of the 16th century is also based on the use of Archimedes' law. The essence of the method is to measure body weight in air, and then in a liquid. If the first value is designated P 0 , and the second - P 1 , then the metal density in kg / m3 is calculated by the following formula:
ρ = P 0 * ρ l / (P 0 - P 1 )
Where ρ l is the fluid density.
Theoretical determination of density
In the above table of densities of chemical elements, red indicates metals for which theoretical density is given. These elements are radioactive, and they were obtained artificially in small quantities. These factors make it difficult to accurately measure the density. However, ρ can be successfully calculated.
The method of theoretical determination of density is quite simple. To do this, you need to know the mass of one atom, the number of atoms in the elementary crystal lattice and the type of this lattice.
For example, we give a calculation for iron. Its atom has a mass of 55.847 amu Iron at room conditions has a bcc lattice with a parameter of 2.866 angstroms. Since there are two atoms per elementary cubic bcc, we obtain:
ρ = 2 * 55.847 * 1.66 * 10 -27 / (2.866 3 * 10 -30 ) = 7.876 kg / m 3
If we compare this value with the table one, we can see that they differ only in the third decimal place.