The Elements

Elementary, My Dear Reader ...

Elements are substances that are made up of only one kind of atom. Gold is an element; if you break it down all you will find are atoms of gold and nothing else. Water, on the other hand, if broken down, is made up of molecules containing atoms of Hydrogen and Oxygen which gives us the famous formula

In this essay, I'm going to describe some of the elements in general terms.

The Hydrogen atom is the simplest of all atoms consisting of a single proton "orbited" by an electron. Because of its one proton we say it has an Atomic Number of 1, or that it is Element No 1. The name comes from Greek words meaning producer of water. This is because when it burns in air, water is produced.

On the Earth, Hydrogen occurs in virtually all organic compounds (along with Carbon). It is rare in its elemental form because it reacts explosively with Oxygen. Its compounds are everywhere.

Water is one of the most important substances on the Earth. It is a liquid over a wide range of temperatures, it dissolves many other substances, it holds heat well acting like a thermostat for the planet, and it freezes from the top. This last property is unusual for a liquid (ever seen wax solidifying?), and means that life can survive under water during winter insulated by a layer of ice. Other substances containing Hydrogen include petroleum (Greek: oil of rock) products, acids and alcohols.

In space, Hydrogen is the most abundant element. Its nuclear reactions within stars provide the energy that powers the Universe and life on Earth. The Evolution of Stars described this in more detail.

Helium is the second most abundant element in the universe. Its atom consists of two protons surrounded by two electrons. Its Atomic Number is therefore 2. In the nucleus of Helium are two more particles that are neutral, neutrons.

The Helium nucleus is a very stable entity. The two electrons are also stable. Helium has little tendency to change or to react with other atoms. Helium forms no chemical compounds whatsoever. Helium atoms don't even join together very easily. Because of this Helium can be cooled to a temperature of -269 degrees Celsius before the atoms come together enough for it to liquefy. Helium has the lowest boiling point of any liquid (just 4 degrees above Absolute Zero). At a temperature of -271 degrees C, Helium begins to act very strangely: it loses all mechanical resistance: the liquid can migrate along the surface of a beaker so that it leaves its container!

Although Helium is the second most abundant element in the universe, it is rare on the Earth. Its light atom is not easily held by the Earth's gravity. Because it doesn't form compounds, it cannot link up with other atoms to become heavy enough to be held on the Earth, like Hydrogen does. The only reason it is found on Earth is that it is constantly being produced. When heavy atoms like Uranium break down (we say they are radioactive), their heavy nuclei throw out Helium nuclei; Helium is a product of radioactive decay.

Interestingly, it was first discovered, not on our world, but on the Sun! When white light is passed through a prism, it is broken down into a spectrum, the colours of the rainbow. If this is done to sunlight, the spectrum is found to be crossed by dark lines. These lines are due to atoms in the sun's gaseous atmosphere absorbing certain wavelengths of the light. Each different type of atom absorbs different wavelengths. In other words, elements leave their fingerprints in the spectrum. When the Sun's spectrum was first examined during the 1860s, most of the lines on the sun could be identified with elements known on the Earth. However, one series of lines could not be. Scientists postulated a new element to explain these lines and gave it the name of the Greek god of the Sun, Helios. By the turn of the century, Helium was located in rocks on the Earth. The biggest uses of Helium are for undersea divers (it lowers the risk of the bends) and for research into very low temperatures.

Read more about The Electromagnetic Spectrum and the information it can yield.

Lithium is element No 3. It is the lightest metal, so light that it floats on water; at least it would do if it didn't dissolve in water. The name is from the Greek, Lithos which means stone.

Carbon is from the Latin for charcoal. It is element No 6. Carbon is the most important element in terms of life on this planet.

The Carbon atom is remarkable in that it can combine with itself and with other atoms in a multitude of ways. The chemistry of Carbon is called Organic Chemistry. There are more carbon compounds than compounds of all the other elements put together. Carbon atoms can link together to form long chains, rings or even balls.

Carbon atoms combine with Hydrogen to form waxes and petroleum. Carbon, Hydrogen and Oxygen combining together form alcohols, fats, organic acids (like Citric Acid in citrus fruits or Ascorbic Acid which is Vitamin C), sugars, starches, and ketones (in perfumes). These three elements along with Nitrogen form Amino Acids which are found in proteins.

The question of life is an interesting one. On Earth all life is based on the chemistry of carbon. Experiments have been performed where simple compounds are subjected to ultra violet light and combine to form simple organic compounds. Meteorites (rocks floating in space) are found to contain organic compounds in traces. Also, gases in interstellar space are found to contain organic compounds. Carbon appears to be the only atom capable of forming such complexity in its chemistry.

The question of whether Extraterrestrial Life exists is a fascinating one.

In elemental form Carbon has two common forms. If the atoms are arranged symmetrically, we have diamond, the hardest substance known. If the atoms are arranged in layers, we have graphite which is used in pencil lead. Two totally different substances, both made up of different arrangements of carbon atoms. These forms are called allotropes of carbon.

Nitrogen is element No 7. The name comes from the Greek for producer of nitre. Nitre is a crystal used in gunpowder.

Nitrogen is the most common gas in the Earth's atmosphere. It is normally unreactive in this elemental state. However during lightning flashes, the intense energy causes nitrogen to combine with oxygen and water to give a weak acid rain. This acid helps put nitrates back into soils so is a natural fertiliser. Nitrogen forms many organic compounds especially Amino Acids. Although life uses about 20 or so Amino Acids, they can combine in countless ways to form all the proteins and enzymes known.

Many explosives, for example Tri Nitro Toluene (TNT), contain Nitrogen.

Oxygen is incorrectly named. The name comes from the Greek for producer of sourness because it was believed that oxygen atoms occurred in acids (which taste sour). Oxygen is not present in all acids. It is element No 8.

Oxygen is the most common element in the Earth's crust, and copious in the atmosphere. In organic chemistry it is found in fats, and sugars. Sucrose (the sugar I put in my tea), for example has a formula of

Oxygen in the atmosphere occurs normally as diatomic molecules (O₂). However, there exists another form with three atoms in a molecule (O₃). This is called Ozone and has the interesting and important property of absorbing ultra violet light. Most of the Earth's Ozone is found in a layer several kilometres above sea level. Its presence there makes life possible on the Earth's land surface.

Water is a compound of oxygen with hydrogen. Although all life on Earth requires water to exist, not all life requires oxygen, indeed for some organisms oxygen is actually poisonous.

Compounds containing oxygen with one other element are called oxides. Different oxides of the same element can exist and these may have different properties depending on the composition.

Hydrogen has two oxides: H₂O - water; H₂O₂ - peroxide used for bleaching. Carbon has two common oxides: CO - the deadly carbon monoxide; CO₂ carbon dioxide breathed out by animals, used by plants. Nitrogen has several oxides including these: N₂O - laughing gas; NO₂ - nitric oxide (an exhaust gas that causes acid rain).

Rust is one of several oxides of iron. Sand and quartz are an oxide of silicon. Several gemstones are impure oxides of metals.

Element No 9. The name comes from a mineral Fluorspar which is German for flowing rock. The reason is that fluorspar is a mineral that is added to other minerals to lower the melting point. This is useful in some forms of mineral extraction.

Fluorine itself is a pale yellow gas. It is the most reactive element known. It reacts with water violently liberating oxygen and forming hydrofluoric acid. This substance attacks glass which is unusual. Most fluorine compounds are poisonous. Organic compounds containing fluorine are the cause of the well known damage to the Ozone layer. These compounds are used in sprays and refrigerants. Some fluorine compounds are very resistant (like Teflon).

Neon (Greek for new) is element No 10. It resembles Helium in being an unreactive (or noble) gas. It forms no compounds. If the gas is placed in a glass tube and has an electric current passed through it, the tube glows with an orange light, just the thing for advertisers!

Sodium is a reactive metal (element 11). It is soft enough to be cut by a knife and reacts violently with water or oxygen. Not surprisingly, it is not found in its elemental state on Earth.

The sodium atom absorbs and emits light in the yellow part of the spectrum, hence the colour of Sodium (street) lights. Its most useful compound is common salt (sodium chloride), essential in the nervous systems of animals. The name comes from soda which is used in cooking. The symbol Na comes from its Latin name Natrium.

This element is named after a white powder called magnesia which is drunk with water to cure indigestion (so called milk of magnesia).

It is a light metal that burns with an brilliant white flame. It used to be used for illumination in primitive photography.

Its importance in life is that it occurs in Chlorophyll (Greek for green leaf). This is the substance that allows plants to convert sunlight into sugars at the beginning of the food chain. It is element 12.

Aluminium (American name: Aluminum) is the most common metal on the Earth's crust, a common component of most rocks. Sapphires are an oxide of aluminium. It is a light metal with many uses in engineering. It is element 13.

Silicon (element 14) is the second most common element on the Earth's crust. It forms extremely stable bonds with oxygen to form various forms of silica. Silica is a component of all rocks along with aluminium and other less common elements. Sand is almost pure silica as are glass and quartz.

The element itself is difficult to extract but fairly stable. It resembles a metallic rock. It is the mainstay of the computer industry and used for converting sunlight into electricity in light cells.

Some have suggested the existence of silicon based life because silicon forms many compounds, especially with Hydrogen. These compounds are all unstable under normal conditions; rocks are the most stable kind of silicon compounds.

Element 15 gets its name from the Greek words bringer of light. The reason is that the element reacts with air and glows as it oxidises. More accurately, one form does.

Phosphorus has two allotropes. The yellow form is soft, poisonous and glows when not under water. The red form is not poisonous and does not react with oxygen unless ignited. The red form is used in matches.

Phosphorus occurs in organic compounds in certain proteins, and is an important constituent of bones and teeth. It is also found in guano which is often used as a fertiliser.

This is the brimstone mentioned in the Bible. Sulphur (American spelling: Sulfur) is normally associated with volcanoes. The bad eggs smell near volcanoes comes form oxides and hydrides of sulphur.

Sulphuric Acid is a very important industrial compound. The element is very important in the processing of rubber. Sulphur occurs in certain proteins (egg yolk). This is element 16.

The name comes from the Greek chloros (green) since the element is a greenish gas. It is found in salt. Its organic compounds are mainly used as industrial solvents, cleaners (like bleach), and pesticides (like DDT). Hydrochloric acid has the formula HCl.

It is element No 17.

From the Latin for stone. The Romans often used stones to count so the word calculate is from the same root.

It is Element No 20 and is found in chalk, marble, bones, teeth and shells.

The element itself is a reactive metal that burns with a crimson flame.

A metal with Atomic Number 24. The name comes from the Greek chroma (colour), because chromium's compounds are highly coloured. It is often added to iron in the making of steel.

The fourth most common element in the crust of the Earth, very common in the Earth's core and in the Universe in general because of the way stars work and the stability of its nucleus. The name comes from an old English word.

Iron has been an important metal historically. It has the rare property of magnetism. Its oxides (rust) are red. Mars has lots of rust on its surface, hence its red colour. Iron is an important constituent of haemoglobin in mammalian blood. Its Atomic Number is 26. The symbol Fe comes from the Latin name for Iron, Ferrum.

The word Copper is from the same root as Cyprus, the first place the reddish metal was found. It is the best conductor of heat and electricity. The copper atom occurs in the blood of crustaceans. It is element 29.

Silver (Atomic Number 47, Latin name: Argentum) has been known from ancient times. Countries like Bolivia were famed for the wealth generated from silver mines. Argentina is named after the metal.

Many Silver compounds are sensitive to light; they are used in black and white photography. The metal is used in jewellery, coinage and electronics.

The name is from the Spanish meaning little silver because it used to be confused with that metal. Platinum is one of the noble metals, very few chemicals corrode it or react with it. Its main uses are jewellery and high quality electrical equipment. It has an Atomic Number of 78.

The word is from old English. Gold is a yellow metal. It is the most malleable of all metals. This means it can be beaten very finely (into gold paper for putting onto images of the Buddha), and drawn to very thin wires. The Incas used gold for everyday objects because it was so common in the Andes.

Its major use today is for a monetary standard. There are some uses in electronics.

Its Atomic Number is 79. The Latin name was Aurum.

Mercury is named after the messenger of the gods because it is the only metal that is liquid at room temperature. Its old name is quicksilver where quick is used to mean alive (as in the old expression the quick and the dead).

It is a dense substance whose properties are used for making thermometers (from the Greek for measure heat) and barometers (from the Greek for measure weight).

It is an accumulative poison associated with an incident in the village of Minimata in Japan. Several years ago, industrial discharges of Mercury into the sea ended up in the fish that the local population ate. The result was Minimata Disease which caused people to lose control of their nervous system. It is element No 80.

The Latin name Hydrargentum (water silver) gives the element its symbol.

Element No 82. Another old English word. The Latin name is plumbum from which we get plumbing, since lead was used for pipes.

Lead is a dense metal with poisonous compounds. Atoms with larger Atomic Numbers than lead tend to be unstable.

Uranium has an Atomic Number of 92. Its nucleus contains 92 protons and 146 neutrons. This is too much. The nucleus is unstable. After a while it will break down and eject what is called an alpha particle. This particle is nothing more exotic than a Helium nucleus, two protons and two neutrons.

The Uranium nucleus will, of course, no longer be Uranium, as its Atomic Number will have decreased by 2.

It will in fact be an element called Thorium (No 90). These strange properties are perceived in the macro world as the phenomenon of radioactivity. The radiations given out are usually dangerous to life because they can damage the delicate chemistry of life.

Some Uranium atoms are different. They still have 92 protons (otherwise they wouldn't be Uranium) but they only have 143 neutrons. The 146 neutron variety is called Uranium 238 (because 92 and 146 = 238). The other variety is called Uranium 235 (92 + 143 = 235). Many elements have atoms which only differ in the number of neutrons, these are called isotopes, from the Greek same place because they are found together and are tabulated together as a single substance.

All isotopes have the same chemical properties. The chemistry of atoms is determined by the arrangement of electrons around the nucleus. So these two types of Uranium cannot be distinguished by chemical means. However because the two types of atoms differ in mass (235 and 238 times the mass of a Hydrogen atom respectively) they can be separated by physical methods. A good way is to produce gaseous compounds (like Uranium Hexafluoride, UF₆) and allow them to diffuse through a barrier. The heavier molecules diffuse slower.

The interesting thing about Uranium 235 is the behaviour of its nucleus when it is struck by a neutron. The nucleus splits into two. This is called nuclear fission. The break up of the nucleus releases vast amounts of energy and produces nuclei around Atomic Numbers 40 to 50 as well as free neutrons. These free neutrons can initiate more fissions and so on. This is called a chain reaction and is the basis of the atom bomb and most nuclear power stations. The element was discovered shortly after the planet Uranus and was named after it.

If Uranium 238 is struck by neutrons, it absorbs one and undergoes some interesting nuclear reactions which involve two neutrons converting themselves into protons. The net effect is to increase the Atomic Number to 94. This is Plutonium.

This element is not normally found in nature but is produced artificially. It is now a by-product from Uranium power stations. Like Uranium 235, it can undergo fission and so is used as a nuclear fuel. Plutonium, however, is one of the most poisonous substances known.

© 1998 Kryss Katsiavriades

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