Beryllium

Beryllium is the fourth element of the periodic table, and its chemical properties only get more metallic the further down you go in its group. Even though lithium is directly to its left, beryllium belongs to the group of alkaline earth metals, which are generally less reactive than the alkali metals. Beryllium is actually the least reactive member of its group, and unlike its heavier relatives, it doesn’t particularly enjoy reacting with water. While calcium and strontium will happily react with water, beryllium mostly just sits there, protected by a thin layer of oxide. How boring.

Beryllium has an atomic mass of 9.0122, atomic number of 4, and it has only 1 stable isotope, Be-9. Be-9 is the only naturally occurring stable isotope of beryllium, making up practically 100% of all natural beryllium. There are also radioactive isotopes, such as Be-7 and Be-10, but these are found in extremely tiny amounts, usually produced when cosmic rays smash into atoms in the atmosphere. Be-10 is particularly interesting because it has a half-life of about 1.39 million years, meaning that it can remain in geological materials for an absurdly long time before finally decaying. All of these isotopes are chemically almost indistinguishable from one another without specialized technology like mass spectrometers. Even though about two percent of the mass in the universe remains for elements other than hydrogen and helium to take up, beryllium makes up a ridiculously small fraction of it. In the Earth’s crust, however, beryllium makes up roughly 0.00028% by mass. (From now on, all measurements will be by mass). In the atmosphere, forget about finding any significant amount. There are tiny amounts of beryllium-containing dust particles floating around, but similarly, unless you work with beryllium, there is a very low chance you will actually inhale it. Unlike lithium, beryllium is also surprisingly toxic when its dust is inhaled, especially over repeated exposures, so perhaps it’s a good thing that the air isn’t full of it.

Beryllium is electropositive, which is another way of saying that it prefers losing electrons rather than gaining them, although it’s nowhere near as eager to do so as lithium. Because of its small atomic size and relatively high charge density, beryllium actually forms a surprising number of covalent bonds, which involve the sharing of electrons between atoms. This makes it rather unusual among the alkaline earth metals, since the heavier members of its group tend to form much more ionic compounds. For example, beryllium chloride (BeCl₂) is largely covalent, while calcium chloride (CaCl₂) is predominantly ionic. Beryllium isn’t a diatomic element either, since it is a metal and forms a metallic crystal structure instead of existing as individual Be₂ molecules under ordinary conditions. All metals have some sort of structure in which they are arranged and a sea of electrons floats around them. That’s why metals are generally solid and often have relatively high melting points, because that metallic bonding keeps them together. Beryllium takes this to another level, with a melting point of approximately 1,287°C, which is ridiculously high compared to lithium’s measly 180.5°C. Its chemical formula is simply “Be”, because if you wanted to write the full chemical formula for a small piece, you’d end up writing “Be1000000000…”. Beryllium’s full electron configuration is 1s²2s², and its noble gas configuration is [He] 2s². Beryllium is the first element to have a completely filled 2s subshell, although its second electron shell is still far from full. Beryllium forms metallic bonds with other metals and beryllium atoms, as well as covalent bonds in compounds like beryllium chloride (BeCl₂) and beryllium hydride (BeH₂). It can also form compounds with significant ionic character, such as beryllium oxide (BeO), although even these have more covalent character than you might expect from a your average alkaline earth metal.