Can we make solid mercury?
All solids can melt at a certain temperature - the melting point. They then change their so-called state of aggregation from solid to liquid (or, with further heating to the boiling point, into the gas state). A different melting point applies to each substance. Metals melt at very different temperatures depending on their chemical composition - cesium, for example, melts at higher room temperatures, tungsten only melts at over 3000 degrees Celsius. This also means that there are very different metals. But there are some properties that all metals share: A metal atom consists of a positively charged atomic nucleus and a negatively charged coating, the electrons. In order to develop the metallic properties, many metal atoms have to come together. A single iron atom is therefore not yet a metal. The metallic properties include, for example, electronic conductivity, which means that the individual atoms share their electrons and these can move easily between the atomic bodies. Other typical properties are the mostly silvery glossy surface and its good deformability. Only a few pure metals, that is, dignified, occur in nature: examples are gold, mercury and silver. Most metals can be found in chemical compounds, ores, bound with oxygen, for example. Usable metals, such as iron, have to be produced chemically. This is a very complex process because it requires a lot of energy in the form of heat or electricity. That is why it is also important that we value and recycle metal as a material.
What happens chemically when metal melts? You can illustrate this with a group of children. Suppose it is cold outside and the children want to warm up. What do you do? They move together like penguin cubs waiting for their parents in the cold of the polar ice. This is also the case with metals: when a metal is cold and below its melting point, the individual atoms that make up a metal are very close to one another. In this solid state of aggregation, the atoms form a fixed order, they are quasi lined up. As soon as the children get warm, they move away from each other again. It is the same with metals: the rigid order is lost, the atoms move, the metal begins to melt and becomes liquid. When the metal is cooled down again, the atoms find their way back to their original order and the substance solidifies again.
But there are some substances, including metals, that react with the air before they reach their melting point. Examples of this are lithium or wood, both of which “burn” in air, which is noticeable through different phenomena: lithium changes color on the surface due to the formation of lithium oxide and nitride there, while wood ignites above a certain temperature. Iron also reacts with air, albeit very slowly, and forms rust. Iron is oxidized and oxygen is reduced. This means that the oxygen takes away electrons from the iron, whereby the iron loses its metallic properties ...
However, iron can be protected against this reaction with air, for example by mixing (= alloying) with other metals and non-metals in order to produce stainless steel. Incidentally, steel is a very diverse metal: there are more than 2000 types of steel with different properties. Steel can be incredibly resistant - just think of an airplane, for example: it might stand in the searing heat somewhere in a tropical country for hours and a few minutes later it has to withstand minus 60 degrees Celsius at an altitude of 10,000 meters. These are temperature differences of over 100 degrees. Metals are fascinating because they make up around 80 percent of all chemical elements and have such different properties. For example lead: although this is a heavy metal, it is also so soft that it can be scratched like wax or used as a pipe seal. Metals have a wide variety of colors from reddish (copper), yellow (gold) or silvery. By the way, silver is the most reflective metal. That is why the mirrors used to be made of silver. In addition, silver also conducts electricity and heat very well. Metals also have so-called superconductors that conduct electricity without resistance, i.e. friction losses. The problem with this is that this is only possible at very low temperatures, i.e. below minus 200 degrees. Of course, metals are also very popular as jewelry. The term metal comes from the Greek, from the word métallon, which means mine or shaft. This probably describes the place where metals were found. Ancient finds of coins and jewelry prove that man recognized the value and beauty of metal very early on.
Our expert Katharina Fromm is Professor of Chemistry at the University of Freiburg. In addition to her teaching and research activities, she is committed to helping children, whom she teaches chemistry in entertaining demonstrations.
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