#910 What is a metal?

What is a metal? A metal is any material that readily loses its outer shell electrons, can be polished to be highly reflective of light, is opaque, conducts heat, conducts electricity, is ductile, and malleable. The bond between the atoms in the molecules cause all of these properties and are what makes a material a metal. There are 118 elements on the periodic table and 95 of them are classed as metal.

The word metal comes from the Ancient Greek “metallon”, which meant “mine, quarry, metal”. It came into English via Latin and French. The first metals that people discovered were copper, gold, silver, and iron, because they are all natural and don’t require any processing. At what point people worked out that metals could be reshaped if they were heated is unknown, but the first metal working comes from Mesopotamia, roughly where Iraq is now, and was from about 8700 BC. All of the natural metals that we have on Earth were formed in the center of stars, probably neutron stars. As stars go through their lifecycle, they burn through each type of fuel, combining the atoms in nuclear fusion to make a heavier element. Only stars as dense as neutron stars can make materials like gold and iron.

The reason for most of the properties of metals comes from the outer electrons on their surface. All electrons travel around the nucleus of their atom in different orbits, depending on how much energy they have. The more energy they have, the further away they are from the nucleus and the less pull the nucleus can exert on them. The electrons that are the furthest away from the nucleus are called valence electrons. When metal atoms bond together, each atom is connected to the next atom in a strong, usually crystalline structure. The bond between each atom is very strong. However, the pull on the outside electrons is not strong enough, and these electrons can break free, creating a sea of free-flowing electrons in the material. This is where the properties of metals come from.

Metals are reflective because of the free-flowing electrons on their surface. When light hits the surface of a metal, the energy in the light is absorbed by the free-flowing electrons and that makes them vibrate more. Electrons don’t like having more energy than is natural and they want to lose it as quickly as possible. They lose it by releasing the energy back out, which is the reflected light we see. Metals are very good at releasing almost exactly the same wavelength of light, making them very shiny. Some metals, such as gold, aren’t able to reflect back the blue light wavelength, which makes them look, well, golden.

Metals are opaque because the free-flowing electrons absorb and reflect the light, without letting it pass through. Even very thin metal materials don’t let light pass. With the slight exception of gold, which can let some light through if it is only about 50 nm thick. Gold leaf will let some green light through.

Metals conduct heat extremely well because of the free-flowing electrons. When the electrons on the outer surface are exposed to thermal energy, it makes them vibrate more, just as with light. However, when they vibrate, they only release some of the energy as light, which is where the color of very hot metal comes from. The rest of the energy they are very easily able to pass on to other free electrons, which also pass the heat energy on. Some metals are far better at conducting heat than others. Silver is the best heat conductor, followed by copper, which is why many chefs use copper pans. The worst conductor is manganese.

For the same reason, metals are also good at conducting electricity. When an electric field is applied to the metal, the free-flowing electrons move through it very easily, in the direction of the field, creating an electric current.

The free-flowing electrons also make metals very ductile and very malleable. Ductile means that a material can be drawn out into a thin wire and malleable means the material can be reshaped without breaking. If you try to reshape a nonmetallic material, such as wood, it is going to squash or break. The bonds between the atoms can’t allow it to be molded. With metals, the free-flowing electrons can move as the atoms are moved, keeping them structurally intact. This is why metals can be drawn into wires or reshaped. Gold is the most malleable of metals. You probably remember movies where somebody bites a gold coin to make sure it is real. Gold can be drawn out into a wire that is one atom thick because the free-flowing electrons keep it together. And this is what I learned today.

Photo by Pixabay: https://www.pexels.com/photo/black-and-gold-machine-60064/

Sources

https://www.studysmarter.co.uk/explanations/combined-science/synergy/metals-and-non-metals/

https://www.britannica.com/science/metal-chemistry

https://en.wikipedia.org/wiki/Metal