Boron. Boron is a metalloid, which means that its properties are a mix of those shown by metals and non-metals. The element has four main polymorphs but none occur naturally on Earth (though some are found in meteoroids). It is also tricky to manufacture without contaminants such as carbon. Crystalline boron is often shiny and black and, like the diamond polymorph of carbon, is extremely hard and a poor conductor of electricity.
Carbon. The most common forms of carbon are diamond, the hardest substance known to man and an electrical insulator, and graphite, which conducts electricity and is soft enough to rub off on a piece of paper (it’s the ‘lead’ in a pencil). Carbon can also be made into more exotic elemental forms, including spherical fullerene molecules, carbon nanotubes, amorphous forms, and pyrolytic carbon, which floats above strong magnets. Under atmospheric pressure carbon does not melt but rather transitions straight to a gas (sublimation).
Nitrogen. Elemental nitrogen, which makes up 78% of the atmosphere, is composed of discrete and quite unreactive molecules of two tightly bound nitrogen atoms (N2). It becomes a liquid at -196 °C, and liquid nitrogen is widely used as a coolant across a wide range of science and industry, due to its very low temperatures, cheapness and ready availability.
Magnesium. Magnesium is a light yet strong alkaline earth metal that, unlike the heavier alkaline earths, oxidises only slightly in air. It is, however, highly flammable and burns with a very intense flame. It will also react (usually slowly) with water, producing small bubbles of hydrogen.
Aluminium. Aluminium’s most notable properties are its lightness, strength, ductility, high reflectivity and resistance to corrosion due to the formation of a thin protective layer of oxide on its surface. It is a good thermal and electrical conductor, but is non-magnetic.
Silicon. Silicon, a metalloid, gives crystals with a blue-grey metallic sheen. The atoms, however, are covalently bonded and arranged in the same way as the carbon atoms in diamond. But while diamond is an insulator, elemental silicon is, famously, a semiconductor. The semiconducting properties can be improved by introducing impurities such as P or N into the crystalline silicon lattice, often through irradiation with neutrons from a nuclear reactor like the one run by ANSTO in Sydney.
Sulphur. Sulphur, also known as brimstone in ancient times, is distinctive for its bright yellow colour. It has more than 30 allotropes, but the usual form is composed of cyclic S8 molecules and is odourless. The infamous smell comes from impurities, and sulphur-based compounds are also responsible for other distinctive smells, including ‘rotten egg gas’ (hydrogen sulphide, H2S), onions and garlic.
Titanium. Titanium is a transition metal with the highest strength-to-density ratio of any metallic element. Although 60% denser than Al, it is more than twice as strong. It is also highly corrosion resistant, relatively ductile and has a high melting point. Its thermal and electrical conductivities are low for a metal. It oxidises rapidly in air, but the oxide forms a passive layer on the surface (only a few nanometres thick) that prevents further oxidation and protects it from corrosion.
Vanadium. Vanadium is a hard, ductile, malleable, silver-grey transition metal. It is electrically conductive but thermally insulating. Its chemistry is notable its multiple oxidation states, which form different coloured solutions in water: lilac (II), green (III), blue (IV) and yellow (V).
Chromium. Chromium is the third hardest element (behind the diamond allotrope of carbon, then boron) but is also brittle. It is known for being highly reflective and tarnish resistant. Many of its compounds are brightly coloured, giving rise to the element’s name (from the Greek chrõma, meaning colour). Compounds in the VI oxidation state are toxic and carcinogenic, while those in the III oxidation state and the metal are not.
Manganese. Manganese in its pure state is silver-grey, but, like iron, it “rusts” (i.e. oxidises) very easily. It is hard and brittle, and displays oxidation states from -III to +VII (though II, III, IV, VI and VII are the most common).
Iron. Pure iron is a silver-grey metal that is ferromagnetic up to 770 °C. It reacts readily with water and oxygen to give hydrated iron oxides (“rust”) and unlike many other metals, where oxidation produces thin layers of oxide that protect the bulk metal, rust takes up a much larger volume, producing flakes that fall away and expose more of the bulk metal. The most common oxidation states are II and III.
Cobalt. Cobalt is a hard, lustrous, silver-grey metal which is ferromagnetic below 1115 °C. Its common oxidation states are II and III.
Nickel. Nickel is a lustrous silver-white metal (with a slight golden tinge when highly polished) which is hard and ductile. It is one of only three elements that are ferromagnetic at room temperature, with the others being Fe and Co (Gd is also magnetic below 20 °C).
Copper. Pure copper is a lustrous red-orange metal, however surface oxidation can result in a brown-black appearance, and green copper carbonate can also form over time on e.g. copper roofing. It is soft, malleable and has very high thermal and electrical conductivity.
Zinc. Zinc is (when oxidation is removed) a silvery-blue metal that is diamagnetic and slightly brittle. Strictly, like Cd and Hg, it is a main group metal, however they are often grouped with the transition metals due to their similar chemistry. The only oxidation state of any significance is II.
Gallium. Gallium is a soft, silvery-blue metal that melts at just 29.76°C – low enough that it can melt in your hands. Once melted it can often form supercooled liquids, which means that it stays liquid when returned to below its freezing point (though ‘seeding’ can induce crystallisation). It will wet (stick to or stain) glass, skin and plastic, has no natural biological role but is non-toxic. Its existence and properties were correctly predicted by the inventor of the periodic table, Dmitri Mendeleev, four years before it was discovered.
Germanium. Germanium is a hard, shiny, grey-white metalloid. Like gallium, its existence and properties were predicted by Mendeleev 15 years before it was discovered. The common allotrope (a-Ge) has the same crystal structure as diamond (carbon) and silicon. Germanium also has the unusual property of expanding as it freezes (like water). It is also a semiconductor, like silicon.
Yttrium. Although yttrium is a d-block transition metal, its chemical properties are similar to the lanthanoids, and thus these elements (and Sc) are commonly grouped together under the name of rare-earth elements (though many are not that rare). It is a soft, silver-coloured metal that is reasonably stable in air due to the formation of a protective oxide layer on its surface (Y2O3). The finely divided metal, however, is unstable and can catch fire at elevated temperatures.
Zirconium. Zirconium is a soft, greyish-white malleable metal when pure, though impurities can make it hard and brittle. It is highly resistant to corrosion by agents such as acids, bases and salt water.
Niobium. Niobium, once known as columbium, is a strong and ductile transition metal. It normally oxidises slowly, however the depth of the natural oxide layer can be increased using an electric current (a process known as anodizing). This changes the colour from its natural silver-grey to a range of vibrant colours which are related to the depth of the oxide layer. This process also works for a number of other metallic elements, notably Al, Ti and Ta.
Molybdenum. Molybdenum is a silver-grey second row transition metal which has a high melting point and a low coefficient of thermal expansion. Like Cr and W, its chemistry is notable for its large range of oxidation states, namely -II to +VI. Mo (and W) also regularly forms high nuclearity clusters and oxoanions (e.g. Mo6Cl142-, Mo8O264-).
Silver. Silver is a soft, lustrous transition metal which has the highest electrical and thermal conductivity and reflectivity of any metal. Its chemistry is typified by insoluble, light-sensitive Ag(I) compounds.
Cadmium. Cadmium is a soft, malleable silver-white metal. Its chemistry is similar to zinc, with the oxidation state II being the dominant one, though cadmium compounds are typically much more toxic.
Indium. Indium is a ductile silvery-white main group metal that is soft enough to be cut with a knife. It has a relatively low melting point, and like its neighbour gallium, it is able to wet (i.e. stick to) glass. Its name comes from the indigo blue line observed in its emission spectrum, which was observed before the element was first isolated.
Tin. Tin has two important allotropes. The usual form is b-tin (‘white tin’), which is metallic, soft and malleable, however below 13°C a-tin (‘grey tin’) becomes stable; this allotrope is non-metallic and brittle. This leads to ‘tin pest’ or ‘tin disease’, where b-tin transforms into brittle a-tin in cold weather. This is thought by some to have played an important role in ill-fated historical events such as Napoleon’s 1812 Russian campaign or Robert Scott’s Antarctic expedition of 1910.
Antimony. The most common form of the metalloid element antimony is a shiny grey metallic form which is both soft and brittle. Less common polymorphs include black and yellow forms, as well as an explosive form which is, fortunately, very rare.
Tellurium. The crystalline allotrope of tellurium is shiny silvery-white, while the amorphous allotrope is brown or black. It is mildly toxic, with poisoning victims often having garlic-smelling breath due to the formation of dimethyl telluride gas ((CH3)2Te). The elements in this group of the periodic table (O, S, Se, Te, Po) are known as the chalcogens. The final element in this group, livermorium (Lv), is also predicted to display chalcogen-like chemistry, but its very short half-life makes it difficult to test.
Gadolinium. Gadolinium is a silvery-white lanthanoid metal that oxidises readily, to form black oxide coating. It is ferromagnetic (and thus attracted to a magnet) below 20 °C and highly paramagnetic above this temperature.
Holmium. Holmium is a silvery lanthanoid metal that will tarnish slowly in air, forming a yellowish oxide. It is reasonably stable in dry air at room temperature, but will burn in air, react with water, and (like all lanthanoids) is not found in its pure form in nature.
Ytterbium. Ytterbium is soft and malleable f-block lanthanoid metal, and like most lanthanoids it will react with oxygen (though much more slowly than the early lanthanoids).
Hafnium. Hafnium is a lustrous, silver-grey transition metal. Its chemistry is very similar to zirconium, which can make them difficult to fully separate industrially. Indeed, much of the hafnium produced retains some level of zirconium impurities.
Tantalum. Tantalum is a hard, chemically inert transition metal that shows high conductivity of heat and electricity, and high resistance towards corrosion. It is chemically similar to niobium, which means that the two elements are commonly found together in most ores. It displays two crystalline phases: the more common alpha phase is relatively soft and ductile, while the beta phase is hard and brittle. The rare 180mTa isotope is ‘metastable’, but its decay is yet to be observed; by comparison, the 180Ta isotope has a half-life of only 8 hours.
Tungsten. Tungsten, sometimes earlier known as wolfram, is a hard third-row transition metal that has the highest melting and boiling points of all the elements, as well as one of the highest densities. It also shows the lowest coefficient of thermal expansion of any pure metal. Its chemistry is notable for the formation of oxoanions such as WO42-, W7O246- and H2W12O406- (the ‘Keggin anion’).
Gold. Gold is a soft and malleable metal, which means it’s often alloyed with other metals (typically silver, copper, palladium or nickel) to make it more structurally sound when used in things like jewellery. It is generally quite unreactive (making it a ‘noble metal’), and is a good conductor of heat and electricity. It is one of the densest elements, and unusually for a metal, it is not grey or silver-white in colour, but reddish-yellow.
Lead. Lead is the heaviest non-radioactive element, and is dense, soft and highly malleable. Both its tensile strength and melting point are low relative to other metals. Freshly cut lead is silver in colour, but it then tarnishes to a dull grey (though it is resistant to corrosion). Its atomic symbol comes from the Latin word Plumbum, which also gives us ‘plumbing’.
Bismuth. Bismuth is a heavy p-block metal that is actually weakly radioactive. The decay of its most common isotope, Bi-209, was only discovered in 2003, and it has a half-life that’s a billion times the age of the universe. The element crystallises as highly reflective silver-grey crystals, or as beautiful multi-hued crystals when very thin layers of oxide are allowed to form on the surface (the colour is determined by the layer thickness).