The second group in the periodic table of elements lists the metals known as the alkaline earths; beryllium, magnesium, calcium, strontium and barium. The group can be found in the table in the second column adjacent to the alkali metals; lithium, potassium, sodium, rubidium, cesium and francium. The dramatic differences in reactivity of the alkali, and alkaline-earth metals can be seen in any number of YouTube.com videos. Pure metallic forms of the alkali metals violently explode when they come into contact with water. The alkaline earth metals don’t explode. But they do fizz and throw off hydrogen gas, just as do the alkali metals. However, the rate of their reaction in water is slower and much less violent than any of the alkali metals. The lack of strong reactivity is due to the fact that the alkaline-hydroxide product produced when an alkaline-earth metal comes into contact with water is only partially ionized, whereas a highly exothermic, completely ionizing reaction occurs when the alkaline-hydroxide product of an alkali metal is produced. Why is that? To know that, one needs to understand the behavior of electrons.
When it comes to atoms, I like to think of the nucleus as a tiny, yet very powerful and demanding boss of operations. The boss’s worker-bee electrons buzz about in gigantic, highly ordered, near light-speed swirls to create highly structured force-fields that mostly do exactly what the boss wants. Sounds like it might be complicated, and it most certainly is, but knowledge of the configuration of outer shell electrons is “all” that it takes to have a basic understanding of the difference in the reactivity described above.
Take beryllium for example, it’s first on the list of alkaline earths and, consequently, has the lowest mass in the group. Its four protons require four electrons for neutrality but that leaves two unstable electrons hanging out in the outer orbit of beryllium’s L-shell. As a result, unlike sodium, which explodes in water to form flaming hydrogen gas plus a completely ionized, strong-base, Na0H, beryllium slowly dissolves in water to form a partially ionized, weak-base, Be(OH)2. And that, in a nutshell, is what happens with each of the alkaline earth metals. All of the alkaline hydroxides of the alkaline earths only partially ionize and by definition produce weak alkaline-base buffers in water, aka: Be(OH)2, Mg(OH)2, Ca(OH)2, Sr(OH)2 and Ba(OH)2.
And I think it is interesting to note that due to their weakly ionizing properties alkaline earth metals can act as effective buffers. For example, gardeners will often add calcium hydroxide lime, Ca(OH)2, to their gardens to help neutralize an acidic soil condition. Since Ca(OH)2 only partially ionizes in damp soil, the extra OH– ions, which the weak base releases, will raise the pH away from acidic toward neutral as OH– , hydroxide-ions, sequester H+, by acting as hydrogen-ion traps. In other words, lime added to soil will suck up the acidic H+ ions by releasing alkaline OH– ions to force the H+ + OH– <==> HOH chemical-reaction to re-equilibrate itself in the direction of 10-7 M, H+ + OH–, equality, i.e., pH 7 neutrality.
The origin of beryllium
I find this part of beryllium’s story to be very interesting. It turns out that a tiny bit of beryllium-9 showed up in the first primordial minutes following the Big Bang, i.e., before everything shut down after the initial 20 minutes of super-hot fusion events that were brought to a halt by the deuteron bottleneck (Wikipedia.org). Beryllium-8 was too unstable to show up at this time but it was more than hot enough then, with plenty of neutrons slamming about in those first 20 minutes, to fuse-up some stable beryllium-9. And it’s beryllium-9 that we can find in Earth’s minerals today and it’s Be-9 that we use today in experiments, metallurgy and products. However, beryllium-9 is relatively rare, and most of what we do find on Earth was assembled billions of years after the Big Bang when newly formed stars became the first supernovae to produce cosmic rays capable of breaking up newly formed larger atoms.
So, even though it is rare, beryllium-9 is what we know and is what we can get our Earthly hands on to do things, but it is beryllium-8 that is an important key to our existence and to the self-assembly by atoms of everything else in OSAU! Why, you might ask? And that is a very good question!
Be-8 is so unstable it only exists as a fleeting ion in the roaring, atomic-fusion furnaces of the universe-assembling factories called stars. The Be-8 atom itself, with its four electrons, never gets to show itself. Instead, Be-8 either decays instantly or goes on, as shown above, to fuse with an alpha- particle to assemble carbon-12. Be-9, on the other hand, is so stable it acts as a fusion dead end that only showed up in minute amount during the first 20 minutes following the Big Bang. Alternatively, it also continues to show up in tiny amounts due to the spalation of larger atomic nuclei.