Elementary

The Periodic Table Explained

James M. Russell

• Publisher: Michael O'Mara
• Year: 2019
• Print ISBN: 9781789293609
• eBook ISBN: 9781789291032
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

The periodic table, created in the early 1860s by Russian chemist Dmitri Mendeleev, marked one of the most extraordinary advances in modern chemistry. This basic visual aid helped scientists to gain a deeper understanding of what chemical elements really were: and, astonishingly, it also correctly predicted the properties of elements that hadn't been discovered at the time. Here, in the authoritative Elementary, James Russell uses his lively, accessible and engaging narrative to tell the story behind all the elements we now know about. From learning about the creation of the first three elements, hydrogen, lithium and helium, in the big bang, through to oxygen and carbon, which sustain life on earth – along with the many weird and wonderful uses of elements as varied as fluorine, arsenic, krypton and einsteinium – even the most unscientifically minded will be enthralled by this fascinating subject. Russell compellingly details these most basic building blocks of the universe, and the people who identified, isolated and even created them.

Elements 1–56

Hydrogen

Category: non-metal Atomic number: 1 Colour: colourless Melting point: −259°C (−434°F) Boiling point: −253°C (−423°F) First identified: 1766

Hydrogen is the simplest possible atom, with a nucleus of only one proton and one electron. It was one of the first elements to be formed after the Big Bang, and remains the most abundant in the universe – even though it has been burning in countless stars, where it is fused into helium, it still makes up more than 75 per cent of the detectable universe and appears in more compounds than any other element.

A light, colourless, highly flammable gas, it is rich on our planet in the form of water (two hydrogen atoms bonded to one oxygen atom). The weak bonds that hydrogen forms in molecules give water its relatively high boiling point, allowing it to exist in liquid form in the Earth’s atmosphere, while at low temperatures, the hydrogen bonds adjust and hold the oxygen atoms apart in a kind of crystal lattice: most substances are denser in their solid state than in their liquid state, but this lattice makes ice lighter than water, which is why icebergs float.

Hydrogen also bonds with carbon to form hydrocarbons, including fossil fuels such as coal, crude oil and natural gas (it is a highly combustible element – when you see a candle burning, this is mostly because hydrogen is released from the oil or tallow and burns when it comes into contact with oxygen). Without hydrogen, we wouldn’t have the heat and light from the constant nuclear fusion of the sun.

The sixteenth-century alchemist Paracelsus was the first to observe the phenomenon that bubbles of a flammable gas are produced when metal is mixed with strong acids. (Chemistry teachers use the mnemonic MASH, to remind students that metals + acids produce salts and hydrogen.) In 1671, Robert Boyle observed the same thing when iron filings were mixed with hydrochloric acid (a compound of hydrogen and chlorine). It was nearly a century later, in 1766, that Henry Cavendish realized this gas was a separate element, though he called it inflammable air, which he wrongly identified as phlogiston. In 1781, when he found that this gas produced water when it was burned, Cavendish suggested that the oxygen it was combining with was ‘dephlogisticated air’. It took the brilliant French chemist Antoine Lavoisier, in 1783, to give hydrogen its current name, which is derived from the Greek for ‘water producer’.

Phlogiston, a Dead Horse

The phlogiston theory, which misled Cavendish, was the now-deceased idea that all combustible bodies contained a fire-like element (named from the Ancient Greek word for ‘flame’). The theory was that substances containing phlogiston became dephlogisticated when they burned. The first cracks in this theory came when it was shown that some metals gained weight rather than losing it when they burned, and Lavoisier more or less disproved it when he used closed vessel experiments to show that combustion requires a gas (oxygen) that has a measurable mass.

Hydrogen is extremely light, one reason why it isn’t commonly found in pure form in the air (it basically just floats away and can escape the atmosphere). It is much lighter than oxygen or nitrogen, which is why it was the first gas used to fill a hot-air balloon. It would also be used in airships (hot-air balloons with a rigid structure) – but the boom in airship (or zeppelin) travel in the early twentieth century came to an abrupt end after the spectacular crash of the passenger airship LZ 129 Hindenburg in 1937.

Hydrogen is used, however, in some NASA rockets, including the main Space Shuttle engines, which are powered by burning liquid hydrogen and pure oxygen. And it could be the clean fuel of the future, replacing fossil fuels in cars, either directly or, more likely, in the form of fuel cells, where it would produce only water vapour as a waste product. There are problems to overcome, though: mass storage of such a highly flammable substance would be risky, and hydrogen is either refined from hydrocarbons, which produces more greenhouse gases, or through electrolysis of water, powered by electricity, which will most likely have been produced using fossil fuels in the first place.

There are many other uses for hydrogen: to produce ammonia for fertilizers, to create compounds such as cyclohexane and methanol (which are used in the production of plastics and medicines), and in the manufacture of margarine, glass and silicon chips, among other important products.

Helium

Category: noble gas Atomic number 2 Colour: colourless Melting point: −272°C (−458°F) Boiling point: −269°C (−452°F) First identified: 1895

Nearly everything in the universe that isn’t hydrogen is helium – all the other elements make up only about 2 per cent of the mass of the universe, in spite of being heavier than the two lightest, simplest elements.

However, helium is not that common on Earth – indeed, it wasn’t until 1895 that we were sure it existed here at all.

As one of the noble gases, helium is the second least reactive element, so, unlike hydrogen, it isn’t extensively captured in compounds. However, like hydrogen, its pure form is lighter than air and prone to escaping the Earth’s atmosphere. We find helium as part of natural gas beneath the ground, where it has been formed during the decay of radioactive elements like thorium and uranium.

Helium does make up about 24 per cent of the mass of the sun: in the extreme temperatures of the star, hydrogen nuclei undergo a process of fusion and helium is formed. This creates huge amounts of energy, and possibly an inexhaustible and environmentally friendly solution to our future energy requirements, although we are probably decades away from recreating the nuclear fusion process on the Earth.

One way to identify elements is by using a spectroscope, an instrument that analyses the differently coloured flames created by different elements to generate a kind of ‘elemental fingerprint’ in which the light is split into a series of coloured lines, rather than a continuous spectrum. During a solar eclipse in 1868, two separate astronomers (Jules Janssen from France and the English Norman Lockyer) noticed that there were some clear lines in the spectrum of the sun that didn’t match any known element. Lockyer suggested this was an undiscovered element and named it helium after the Greek sun god Helios. The ‘-ium’ ending shows that he assumed it was a kind of metal, as this is the only non-metal element which takes that ending. Over subsequent decades there was no further evidence of the existence of helium, though Lockyer was vindicated in 1895 when chemist William Ramsay found traces of helium in the gas given off by a chunk of uranium that had been treated in acid; the helium had already formed within the rock but was released as the acid dissolved part of the surface.

The Mickey Mouse Effect

After helium was found in American natural gas deposits, the first helium production plant (which supplied the army with gas for its barrage balloons) opened in 1915 in Texas. From 1919, the US Navy experimented with gas mixes to combat the problem of nitrogen narcosis in deep-sea divers. In the notes from a 1925 experiment, divers breathing a helium and oxygen mixture complained that the change in vocal characteristics had made communication difficult. (The comical squeakiness is caused by soundwaves, which travel faster in any gas that is lighter than air.) Over time, helium was produced more extensively and used to fill party balloons, at which point a new generation of children learned the same trick for themselves.

Helium has the lowest boiling point of any substance and can be used in supercooling other substances; it’s used, for instance, in the Large Hadron Collider, in superconducting magnets such as those in MRI scanners, and to cool the liquid hydrogen used in some NASA rockets. (Supercooling is the process of reducing the temperature of a substance to below its freezing point without it turning into a solid.) Some car airbags contain helium, because it diffuses so rapidly when decompressed (although nitrogen and argon are also used for this purpose).

There is reason to worry about our supply of helium. The market price has crashed since the 1990s’ privatization of US stocks, but it is a limited resource, which is only replenished very slowly within the planet. So, while helium party balloons are fun, bear in mind that the helium from them can escape and leave the atmosphere, so they may not be the smartest way to use this particular noble gas.

Lithium

Category: alkali metal Atomic number: 3 Colour: silvery white Melting point: 181°C (358°F) ...

Table of contents

• Cover
• Title Page
• Copyright
• Contents
• Introduction: Mendeleev’s Brilliant Idea
• Elements 1–56
• The Lanthanides
• Elements 72–94
• Elements 95–118
• Element 119 and Beyond
• Index