A table with gaps in it
In 1869 the Russian chemist Dmitri Mendeleev arranged the known chemical ELEMENT types in order of the weight of their atoms, grouped so that elements that behave alike fell into the same column. The pattern was so strong that where it did not fit, he left gaps, and predicted that elements not yet found would fill them. He even described what they would be like. When gallium was discovered in 1875 and germanium in 1886, their properties matched his predictions closely, and chemists were convinced.
There are now 118 known elements. The newest four were named in 2016: nihonium, after Japan; moscovium, after Moscow; tennessine, after the American state of Tennessee; and oganesson, after a Russian scientist.
Four elements from one village
Elements are named after all sorts of things: gods, planets, colours, scientists and places. A single quarry near the small village of Ytterby, outside Stockholm in Sweden, gave its name to four: yttrium, ytterbium, terbium and erbium, all first found in rock dug there. HELIUM is named after the Greek word for the Sun, because it was discovered in the Sun's light, by studying an eclipse in 1868, nearly thirty years before anyone found it on Earth.
Each element has a one- or two-letter SYMBOL, and some come from old Latin names rather than English ones. That is why GOLD is Au, from aurum; SILVER is Ag, from argentum; IRON is Fe, from ferrum; SODIUM is Na, from natrium; and POTASSIUM is K, from kalium. Lead's symbol has a story of its own, told on our trades page.
Some elements are wild
Down the left-hand side sit the most REACTIVE metals. LITHIUM, sodium and potassium are so eager to react that they are stored under oil, and dropped into water they fizz across the surface, with potassium bursting into lilac flames. At the far right sit the noble gases, such as HELIUM, NEON and ARGON, which barely react with anything at all. Neon glows red-orange when electricity passes through it, which is how the first neon signs were lit. Metals burned in fireworks give off their own colours, as our holidays page explains.
MERCURY is the only metal that is liquid at room temperature. All the gold ever mined in human history would fit into a cube about 22 metres along each side.
The elements that make you
Just a few elements make up almost all of a living body: OXYGEN, CARBON, HYDROGEN and NITROGEN, with CALCIUM in bones and teeth, and small but vital amounts of iron in blood, MAGNESIUM, ZINC, COPPER and SULFUR. The air you breathe is mostly nitrogen, about 78 per cent, with about 21 per cent oxygen and nearly one per cent argon. Our chemistry page covers how the atoms of these elements join together.
Elements made by people
About ninety elements occur naturally on Earth. Almost all the rest have been made by scientists, by smashing atoms together in particle accelerators or in nuclear reactors. The first element made artificially, technetium, was produced in 1937, and its name comes from the Greek for artificial. The heaviest elements are so unstable that they exist for only a tiny fraction of a second before breaking apart, and only a handful of atoms of oganesson have ever been made.