Metals are chemical elements that make up most of the periodic table of D. I. Mendeleev. In this article, we will consider such an important physical property as density, and also give a table of the density of metals in kg / m3.
Density of matter
Before we deal with the density of metals in kg/m3, let's get acquainted with the physical quantity itself. Density is the ratio of body mass m to its volume V in space, which can be written mathematically as follows:
ρ=m / V
The value under study is usually denoted by the letter of the Greek alphabet ρ (ro).
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 may differ significantly from the average.
As you can see from the formula, the value of ρ is expressed in kg/m3in the SI system. It characterizes the amount of a 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 / m3is different, allowing them to be identified.
Metals and their density
Metallic materials are solids at room temperature and atmospheric pressure (mercury is the only exception). They have high plasticity, electrical and thermal conductivity and have a characteristic luster in the polished state of the surface. Many properties of metals are associated with the presence of an ordered crystal lattice in which positive ionic cores sit at the nodes, connected to each other by means of a negative electron gas.
As for the density of metals, it varies widely. So, the least dense are the alkali light metals, such as lithium, potassium or sodium. For example, the density of lithium is 534 kg/m3, which is almost half that of water. This means that lithium, potassium and sodium plates 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 the ρ of water.
The table below shows the density of metals. All values refer to room temperature in g/cm3. If these values are multiplied by 1,000, then we get ρ in kg/m3.
Why are there high density metals and low density metals? The fact is that the value of ρ for each specific case is determined by two mainfactors:
- Feature of the crystal lattice of the metal. If this lattice contains atoms in the most dense packing, then its macroscopic density will be higher. FCC and hcp lattices have the densest packing.
- Physical properties of the metal atom. The larger its mass and the smaller the radius, the higher the value of ρ. This factor explains why high-density metals are chemical elements with a high number in the periodic table.
Experimental determination of density
Suppose we have a piece of unknown metal. How can you determine its density? Recalling the formula for ρ, we arrive at the answer to the question asked. To determine the density of the metal, it is enough to weigh it on any balance and measure the volume. Then the first value should be divided by the second, remembering to use the correct units.
If the geometric shape of the body is complex, then it will not be easy to measure its volume. In such cases, you can use the law of Archimedes, since the volume of the displaced liquid when the body is immersed will be exactly equal to the measured volume.
The method of hydrostatic weights, invented at the end of the 16th century by Galileo, is also based on the use of the law of Archimedes. The essence of the method is to measure body weight in air and then in liquid. If the first value is denoted by P0, and the second by P1, then the metal density in kg/m3 is calculated using the following formula:
ρ=P0 ρl / (P0 - P 1)
Where ρl is the density of the liquid.
Theoretical definition of density
In the above table of the densities of chemical elements, the metals for which the theoretical density is given are marked in red. These elements are radioactive, and they were obtained artificially in small quantities. These factors make it difficult to accurately measure their density. However, the value of 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, let's take a calculation for iron. Its atom has a mass of 55.847 amu. Iron under room conditions has a bcc lattice with a parameter of 2.866 angstroms. Since there are two atoms per elementary bcc cube, we get:
ρ=255, 8471, 6610-27 / (2, 8663 10 -30)=7.876 kg/m3
If we compare this value with the table one, we can see that they differ only in the third decimal place.
