Elements are the chemical building blocks of all matter. There are currently 116 elements, with 88 elements occuring naturally on Earth. Now you may be thinking, "Wait a second. I know uranium occurs naturally on Earth and it's element 92!" Well, technetium (#43), promethium (#61), astatine (#85), and francium (#87) form no stable isotopes, although the latter two have been found in the crust in picayune quantities so some do consider them to occur naturally. To make things more complicated, uranium deposits located next to beryllium ores can result in small amounts of the higher elements of neptunium and plutonium. Promethium and technetium have even been detected in the spectral lines of some stars in a galaxy far, far away, but I digress.
Hydrogen is the lightest and most abundant element in the universe. It is a highly flammable and reactive gas so on Earth it's almost always bound up in compounds. It forms explosive mixtures with air and upon combustion it only produces water. It is non-toxic (although like any gas other it can lead to asphyxiation) so I feel pretty comfortable working with it. Industrially, more than 90% of hydrogen is produced by reacting water vapor with methane and other hydrocarbons (fossil fuels) under high pressures and temperatures and in the presence of a nickel catalyst.
CH4 + H2O --> CO + 3H2
In the lab, hydrogen can be produced through the electrolysis of water. It can also be created by the action of an acid on a reactive metal. A common example is the reaction of zinc and hydrochloric acid.
Zn + 2HCl --> ZnCl2 + H2
A reaction that I often use to produce small batches of hydrogen quickly is that between sodium hydroxide and aluminum.
Al + NaOH + H2O --> NaAl(OH)4 + H2
Our friend hydrogen has been receving a lot of attention lately with the energy crisis and rising gasoline prices. As much as I love hydrogen, the fact reamins that hydrogen is not an energy source. Hydrogen is however, a useful way of storing energy, and that energy can be released in a green manner through either combustion or a fuel cell (I had a fun time sucessfully building one of these, although its discussion is slightly beyond the realm of this site). Most of the hydrogen produced right now comes from fossil fuels, which defeats its entire purpose as a environmentally-friendly alternative fuel! What we really need is the solar-hydrogen revolution, where photovoltaic cells provide the electricity needed for the electrolysis of water. In this energy utopia, photovoltaics replace our coal power plants and hydrogen replaces our gasoline.
My infatuation with sodium probably stems from the fact that it reacts violently and, when in large enough quantities, explosively with water, burning with a brilliant yellow flame. This is the one reaction that got me interested in chemistry years ago. Although I have never prepared sodium, I do have a route for its synthesis in mind and want to try my hand at making it some day. Sodium is a grey metal that is soft enough to be cut with a knife. It reacts rapidly with the oxygen in the air so it must be stored in mineral oil, xylene, or the like. Sodium has a fairly low melting point and it forms a very reactive alloy with potassium that is a liquid at room temperature. Its neat reaction with water can actually be put to use as it is a wonderful drying agent- it dries ether like nothing else. It reacts with alcohols, reduces esters, and in general, is an important reagent in organic chemistry. If I ever have a chance at making powerful reducing agents such as sodium hydride and sodium borohydride, I will need to make metallic sodium first. Industrially, sodium is produced by electrolysis of sodium and calcium chloride, the latter significantly reducing the melting point of the salt mixture.
Nickel is a silvery-white coinage metal that is in the same family as platinum. Hence it shares many of the noble and useful characteristics of platinum but is far less expensive- perfect for the amateur chemist. In many instances, it can be used as a less effective substitute in operations in which platinum is required as a catalyst. It is one of the five magnetic elements and it dissolves in hydrochloric and sulfuric acids, forming beautiful green solutions. It is however, resistant to alkalis even at high temperatures, thus making a nickel crucible a good candidate for sodium production. I get my nickel by purifying the nickel in nickel-cadmium batteries. If you're ambitious, you could isolate it from the five-cent coin although you'd be dealing with 75% copper. Raney nickel is a versatile catalyst that can help hydrogenate a wide variety of organic compounds with double or triple bonds. It is a porous alloy of nickel and aluminum and is something I would not mind synthesizing in the future. There is also an entire organonickel branch of chemistry that I know little about.
Magnesium is one maverick of an element! It is the most reactive metal that does not react with water at room temperature. Throw a piece into some boiling water, however, and you’ll mistake it for sodium! It reacts vigorously with all strong acids including hydrochloric, nitric, and sulfuric acids. Magnesium is synthesized by electrolyzing molten magnesium chloride. It is much lighter than but almost as strong as aluminum, and hence finds many applications in the aerospace industry and structural engineering. The great thing about magnesium is that you can easily purchase a bar of it as a magnesium fire starter because it burns at a very high temperature (2200 C or 4000 F) with a blinding white light. Although magnesium can be rather difficult to ignite itself, its high burning temperature makes it useful for igniting pyrotechnic mixtures such as ferroaluminum thermite. Magnesium fires are very difficult to extinguish because the metal reacts with nitrogen, oxygen, and carbon dioxide, three of the primary components of air. Magnesium’s reactivity allows it to participate in its own interesting thermite reactions that can yield metals as varied as sodium, iron, and silicon.
2Mg + SiO2 --> 2MgO + Si
By far the most remarkable feature of magnesium is its ability to form the Grignard reagent, discovered by Victor Grignard who received the 1912 Nobel Prize in Chemistry for his work. When finely divided magnesium is mixed with dry ether or tetrahydrofuran and an alkyl or aryl halide, an organometallic compound known as a Grignard reagent is formed. These are extremely versatile compounds that can be used to synthesize a wide variety of organic groups including alcohols, ketones, and carboxylic acids.