The softest metal in the world

Metals are a kind of materials that have been used by humans since ancient times. This group of substances is very numerous, but they all have common physical characteristics, which are commonly called metallic properties. Hardness among them is usual, but not determinative. More specific are the others, which the most soft metal possesses. These properties are determined by the features of their structure at the molecular level.

Properties of metals

Iron and its alloys (steel, cast iron), copper, aluminum ... The use of these materials marked jerks of scientific and technological progress at different stages of civilization. Each of these metals has characteristics that give it a unique practical value. Common features for them are high thermal and electrical conductivity, plasticity - the ability to maintain integrity during deformation, metallic luster.

Damascus blade, chopping iron armor, and the softest metal, on which traces of slightest impact remain, have a similar internal arrangement. At its core is a crystal lattice, at the nodes of which there are atoms with a positive and neutral charge, between which there is an "electron gas" - particles that left the outer shells of atoms due to weakening of the connection with the nucleus. A special metallic connection between the positive ions located at the lattice sites is due to the attractive forces arising in the "electron gas". The hardness, density, and melting temperature of a metal depend on the concentration of this "gas".

Criteria for evaluation

The answer to the question of what kind of metal is the softest will always be the subject of discussion if we do not agree on the evaluation criteria and determine the very concept of softness. The opinion on this characteristic of the material will be different for specialists of different industries. A metallurgist can understand softness as increased ductility, a tendency to perceive deformations from abrasive materials, and so on.

For materials scientists it is important to be able to objectively compare different characteristics of substances. Softness should also have generally accepted evaluation criteria. The softest metal in the world should have universally recognized indicators, proving its "record" characteristics. There are several techniques, the purpose of which is to measure the softness of different materials.

Methods of measurement

The majority of certified methods for measuring hardness are based on the contact effect of the hardened body, called the indenter, measured by means of precise instruments. Depending on the type of indenter and on the methods of measurement, there are several basic methods:

Brinell's method. The diameter of the impression left by the metal ball is determined when pressed into the surface of the test substance.

- The Rockwell Method. The depth of indentation into the surface of the ball or diamond cone is measured.

The Vickers Method. The area of the impression left by the diamond tetrahedral pyramid is determined.

Shore hardness. There are scales for very hard and very soft materials - the depth of immersion of a special needle or the height of a rebound from the surface of a special striker is measured.

Mohs hardness scale

This scale for determining the relative hardness of minerals and metals was proposed in the early 19th century by the German Friedrich Moos. It is based on the method of scratching, when a harder sample leaves a mark on the softer, and is very convenient for finding out which metal is the softest. In relation to the 10 reference minerals to which the conventional hardness index is assigned, the location of the test substance and the digital index are determined for the test substance. The softest reference mineral is talc. It has Mohs hardness - 1, and hardest, diamond - 10.

The evaluation of hardness according to the Mohs scale is based on the principle of "softer - harder". Precisely determine how many times, for example, aluminum, having an index on the Mohs scale of 2.75, is softer than tungsten (6.0), can only be measured by results based on other methods. But to determine the softest metal in the periodic table of this table is enough.

The softest are the alkali metals

From the Mohs mineralogical scale it can be seen that substances that are related to alkali metals are the mildest. Even mercury, which is familiar to many in liquid from a thermometer, has a hardness index of 1.5. Mildly several substances with similar physico-mechanical and chemical properties: lithium (0.6 on the Mohs scale), sodium (0.5), potassium (0.4), rubidium (0.3). The softest metal is cesium, having a Mohs hardness of 0.2.

The physical and chemical properties of alkali metals are determined by their electronic configuration. It is only slightly different from the structure of inert gases. An electron located at an external energy level has a mobility that determines high chemical activity. The softest metals are characterized by a special volatility, they are difficult to extract and keep unchanged. They are characterized by violent chemical interactions with air, water, oxygen.

Element number 55

The name "cesium" comes from the Latin caesius - "sky blue": in the spectrum radiated by a highly heated substance, two bright blue strips are visible in the infrared range. In its pure form, it reflects light very well, is similar to light gold and has a silvery-yellow color. Cesium is the softest metal in the world, the Brinell hardness index is 0.15 MN / m ² (0.015 kgf / cm ² ). Melting point: + 28.5 ° C, therefore under normal conditions, at room temperature, cesium is in a semi-liquid state.

It is a rare, expensive and extremely chemically active metal. In electronics, radio engineering and the chemical industry of high technologies, cesium and alloys based on it are increasingly used and the need for it is growing constantly. Its chemical activity, the ability to form compounds with the highest electrical conductivity are in demand. Cesium is an important component of the production of special optical instruments, lamps with unique properties and other high-tech products. At the same time, softness is not the most demanded quality.