Innholdsfortegnelse for Understanding Chemistry i Understanding Chemistry

Chemistry is at the crux of all matter. Everything in our universe is made up of atoms. The way in which the components of these microscopic building blocks are structured defines the substances they make up, their properties and behaviours and the way in which these elemental chemicals interact with one another to create new forms of matter. Inside the pages of Understanding Chemistry, you will discover how chemical processes shape our modern lives – from fuelling car engines and powering smartphones to creating our favourite alcoholic beverages and washing our hair.…

Add this to the pile of mind-bending atom qualities: an atomic nucleus has less mass as a whole than its protons and neutrons would have separately. How is this possible? Well, when the nucleus is formed, some of the mass of its constituent parts changes into energy that binds the protons and neutrons together. In other words, there’s high potential energy locked up in the nucleus of the atom. It’s possible to release this energy, and actually harness it, by splitting specific types of atoms apart into multiple fragments – a process known as nuclear fission. All you need to break apart a uranium-235 atom is a slow-moving free neutron. The uranium atom will absorb the free neutron, the extra energy makes the uranium nucleus highly unstable, and the atom…

All matter is made up of atoms – these are tiny particles that cannot be seen through the lense of a conventional microscope. Atoms make up the table of elements, and all elements are made up of the same parts: protons, neutrons and electrons. The atoms of a particular element are all the same as each other, as they all contain the same number of protons in their nuclei. A compound contains atoms of two or more different elements, which are chemically joined together. Water is a compound that contains two hydrogen atoms and one oxygen atom. A mixture is a substance consisting of different atoms, molecules or compounds that aren’t chemically joined. Air, for example, is a mixture of nitrogen, oxygen, argon and others. “Substances in mixtures are not…

DNA is not the only genetic molecule in nature; organisms also make strands of genetic material called RNA. Chemically the two molecules are quite similar, but they have very different roles to play. DNA forms stable double strands that carry the entire genome safely from one generation to the next. RNA forms unstable single strands that carry smaller amounts of genetic data for shorter amounts of time. Cells use RNA to make temporary copies of their genes. These copies act as templates for the molecular machines that make proteins. The machines read through the code three bases at a time, adding the corresponding amino acid to a growing protein string.…

Carbon is so versatile and so important that the Royal Society of Chemistry call it the ‘King of the elements’. It’s everywhere, and we use it for everything. Carbon sits at position six on the periodic table. It has six protons, six neutrons and six electrons. Two of those electrons fill up an electron shell close to the nucleus, while the other four sit in a half-empty shell around the outside. These outer electrons, known as the valence electrons, are the key to carbon’s incredible properties. The electrons in an atom’s outer shell are the ones that take part in chemical bonds. How many bonds depends on how much room there is in the shell, and the amazing thing about carbon is that it’s got space for four. This means…

Human activities like burning fossil fuels and processing metals generate around 90 per cent of the sulphur dioxide in the atmosphere. This sulphur reacts with water to produce sulphuric acid and with other emission products to create sulphur salts. These new compounds fall back to Earth, often in the form of acid rain. This type of acid deposition can have catastrophic effects on natural communities, upsetting the chemical balance of waterways, killing fish and plant life. If particularly concentrated, acid rain can even damage buildings and cause chemical weathering. However, the environmental impact of sulphur pollution isn’t entirely negative; atmospheric sulphur contributes to cloud formation and absorbs ultraviolet light, somewhat offsetting the temperature increases caused by the greenhouse effect. In addition, when acid rain deposits sulphur in bodies of wetlands, the sulphur-consuming…

The pH of a solution tells you what concentration of hydrogen ions it contains. The scale runs from 0 to 14. In mathematical terms the pH number is the negative logarithm of the concentration of hydrogen ions in a solution. Put simply, for every step up you go on the pH scale, there are ten times fewer hydrogen ions in solution. At pH0, the concentration of hydrogen ions is 1 mol dm-3, at pH1, it’s 0.1 mol dm-3, at pH2, 0.01 mol dm-3 and so on. Indicator solutions reveal the pH of unknown liquids because they change colour when they react with H+ or OH-ions. The most well known indicator is litmus, which turns red in acids and blue in alkaline solutions, but a universal indicator gives an even clearer…

With hundreds of people taking a dip each day, public swimming pools are a prime place for water-borne diseases, such as E. coli, to spread. Thankfully, a clever chemical can be used to keep your splashing sanitary. When chlorine is added to pool water, it dissolves to form hypochlorous acid, a weak acid that acts as a disinfectant. It kills bacteria through a process called oxidation, which destroys protein structures inside the bacterial cells, causing them to die. As the water becomes more acidic, the hypochlorous acid itself splits up to form hypochlorite ions, which are less efficient at cleaning water. Therefore, for more effective disinfection, as well as comfortable swimming, the acidity of the pool water must be continuously monitored and kept at a neutral pH between 7.2 and…

It’s possible to smell rain before it has even fallen. Lightning has the power to split atmospheric nitrogen and oxygen molecules into individual atoms. These atoms react to form nitric oxide, which in turn can interact with other chemicals to form ozone – the aroma of which is a bit like chlorine and a specific smell we associate with rain. When the scent carries on the wind, we can predict the rain before it falls. Another smell associated with rain is petrichor – a term coined by a couple of Australian scientists in the mid-Sixties. After a dry spell of weather, the first rain that falls brings with it a very particular aroma that is the same no matter where you are. Two chemicals are responsible for the production of…

Also known as quicksilver, mercury is a heavy metal occurring naturally on Earth. It is the most common of five metals that are a liquid at room temperature. Compared to other metals, mercury is a poor conductor of heat but a good carrier of electricity. It is most commonly found in rocks such as mercuric sulphide inside the ore cinnabar. Mercury is extracted by heating and compressing this ore. Inside a mercury atom, the electrons are very tightly held together. For this reason the bonds between the atoms are very weak as they do not share electrons easily. The small amount of heat present at room temperature is enough to break the bonds between the atoms, which is why mercury is a liquid at such a low temperature. Other metals,…

The first alloys that humans turned into tools and weapons came from space; people used iron and nickel mixtures brought to Earth’s surface by meteors. Then, around 2500 BCE, someone mixed copper with tin to create bronze. The resulting alloy was much harder than its ingredients, and gave its name to the Bronze Age. Since then we’ve invented even more alloys. In the 19th century removing impurities from steel made it reliably strong, starting the Industrial Revolution. After World War II, Russia and the US wanted faster, lighter spy planes. That led to scientists developing low-weight, high-strength titanium alloys.…

The explosive nature of thermite makes it a suitable ingredient for making incendiary bombs. What’s particularly devastating about thermite bombs is their ability to rain down molten metal. Following the ignition of the thermite reaction by a fuse, the burning metals erupt in a firework-like explosion, maintaining thousand-degree temperatures as they fall to the ground. Not long after the discovery of thermite, the German military enlisted it as a weapon. In 1915, during World War I, thermite bombs were deployed by German forces in Zeppelin raids on England. During World War II, thermite bombs got an upgrade with more energetic elements, such as copper and magnesium, to maximise the damage they could cause. The use of thermite bombs is now regulated under Protocol III of the UN Convention on Certain Conventional…

Toxic substances include anything that can physically harm us after we inhale, swallow or touch it, from an innocent bee sting to full-blown cyanide poisoning. Defining toxicity is tricky since almost anything is poisonous at high enough doses – even water. Acute poisoning follows just one exposure, for example, nibbling a death cap mushroom, but chronic exposure – like inhaling cigarette smoke over decades – can be equally, if not more, damaging. Toxins are toxic substances produced by living organisms. These organisms use toxins mainly to ward off predators or paralyse prey. Small but deadly bacteria produce some of the most potent toxins known, including botulinum toxin A (Botox). Other toxic substances occur naturally on Earth, such as the hydrogen sulphide produced by volcanic eruptions. We humans have even invented…

Explosions are deadly for a variety of reasons. The basis of any explosion is the rapid burning and decomposition of a material, a process that creates a large amount of heat, pressure and gas in a short amount of time. All of these factors can have an effect on humans, as their physical thresholds to withstand the various forces and chemicals in play is easily broken. For example, the heat generated by an explosion of HMX (a nitroamine high explosive) reaches thousands of degrees Celsius in just a matter of seconds. This is something the skin of a human – which would swiftly be subjected to third-degree burns – could not withstand, with the skin tissues and structures destroyed. The force and velocity of the detonation is equally as deadly. The shock…

Organic: Many explosions are caused by plants and trees when subjected to hot and volatile conditions. For example, the Eucalyptus tree – which is predominantly found in Australia, New Guinea and Indonesia – is often prone to spontaneous combustion in periods of sustained heat and dry conditions. This is caused by the tree’s high oil content (ie Eucalyptus oil) that rises above the bush as vapour when heated sufficiently, creating a characteristic haze in dense forested areas. This oil, in liquid and vapour forms, is incredibly flammable and if environmental pressure and heat reach critical levels, is prone to combust. This factor is severely exacerbated when a forest fire passes into Eucalyptus-heavy areas, as the resulting explosions and general flammability of the tree’s bark carries and generates fire quickly. Volcanic:…

There are two main types of smoke detector: optical and ionisation. Optical detectors contain an infrared light beam pointing toward a photocell, which generates electricity when light falls on it (like on solar panels). When there is no smoke, the light reaches the photocell unobstructed. This is registered by the internal circuitry so the alarm is not triggered. When there is a fire, smoke enters the detector and blocks the beam of light, so the photocell can no longer produce an electric current. This change is picked up by the circuitry, triggering the alarm and alerting people to danger. Ionisation detectors contain a small sample of a radioactive substance, typically americium. This constantly emits alpha particles (positively-charged helium nuclei), which pass between two charged metal plates called electrodes. The alpha…

Lighting a match inside a giant, oxygen-filled research centre floating in space doesn’t sound like the safest idea. However, in 2012, astronauts aboard the International Space Station (ISS) did just that. With a lack of oxygen throughout space, the only way to see how fire reacted in microgravity was to strike a match aboard the ISS. The teardrop shape of a flame on Earth is due to the uptake of oxygen as it burns. However, in microgravity, the same rules don’t apply. Without an abundance of rising oxygen, space flames are shaped merely by the static air around them. This creates a spherical flame as the chemical reactions creating light occur all around the match.…

Like in many other industries, artificial intelligence (AI) has found its way into the toolset of firework display designers. Along with being able to simulate a digital display, AI is being used to gather data from displays around the world to choreograph new and unique experiences. AI is capable of precisely calculating the optimal timing, position and safety of fireworks to produce a display that’s not only visually exciting, but one that is perfectly synchronised with any accompanying music. It can even be used to respond to changes in the weather in real time, such as adjusting the position of a launching mortar to account for changing wind speed.…

In many ways, during the Middle Ages, distillation was the alchemist’s greatest tool. Through controlled heating of a liquid or solid source material, the alchemist could draw out and isolate pure vapours that were cooled, condensed into liquid and employed in the mystical medicinal research. Distillation also helped the ancient Greeks to purify fresh drinking water from the sea. It drew pungent oils out of flowers and herbs for perfumes and early medicines. And it took humble beer and homemade wine and refined them into finely crafted, high-octane spirits that earned the name aqua vitae, or the water of life. Today, distillation remains a critical chemical process for isolating pure compounds from a mixed solution. The science of distillation is rooted in the fact that every molecular compound has its…

People often report cravings for particular foods, and that eating certain meals makes them happy. As a species, we evolved to make eating a pleasant experience, encouraging us to seek out high-calorie food to sustain ourselves when food was scarce. The human brain has developed reward pathways associated with eating fat and sugar, which release mood-enhancing neurotransmitters, like dopamine and endorphins. Probably the most-studied example is chocolate, which contains phenylethylamine and this affects the body’s opioid production. Comfort food, on the other hand, works more psychologically, and the pleasant feelings that it induces are often linked to sight, smell and taste, which can trigger a sense of nostalgia.…

Gels When experimenting with textures, chefs are able to turn liquids into solids by adding a gelling agent called a hydrocolloid. Common hydrocolloids used in cooking include gelatine, agar-agar and sodium alginate and are made of tightly-wound coils of long protein or carbohydrate molecules. When added to liquid, the molecules evenly disperse and then heat is applied to cause them to hydrate and unfurl. As the mixture cools back down again, the long strands form a crosslinked network that traps the liquid molecules and forms a solid shape. The result is a firm gel or jelly packed full of the flavour of the original liquid. Liquid nitrogen To introduce some drama to their food presentation, chefs can garnish their drinks and dishes with a dash of liquid nitrogen to produce…

Everything in the universe is made of countless tiny atoms that are joined into different structures, essentially like toy building blocks. But instead of snapping together through friction, like plastic blocks, atoms snap together through electrical charge. At the centre of every atom you’ll find the nucleus – a blob of positively charged particles called protons and neutrally charged particles called neutrons. The tiny nucleus is surrounded by even smaller negatively charged particles called electrons. Usually, there is an equal number of protons and electrons. Because of their opposite charge, these protons and electrons are attracted to each other, which is what holds the atom together. With this balance, the atom is electrically neutral. But these electrons are a fickle bunch: they’re not only attracted to their own atom’s nucleus…

All of the 118 elements in the periodic table are made from the same three key ingredients – protons, neutrons and electrons. The protons and neutrons make up the nucleus at the centre of each atom, while the electrons whizz around the outside and make chemical bonds with other atoms. The identity of each atom is determined by the number of protons in its nucleus, known as the atomic number. Hydrogen has one, helium has two, lithium three, and so on. The periodic table lists the elements in this order. Protons are positively charged, while electrons are negatively charged; an atom will have an equal number of each. The electrons are arranged in ‘shells’ around the nucleus. Each row of the periodic table represents a new layer of electron shells, and…

A stretched carbon fibre is twice as strong as steel but only a quarter of the density. Woven into mats and embedded in epoxy resin, this tough, flexible material is stiff, strong under tension and resistant to chemicals. It’s resilient enough to build lightweight bikes, boats, cars, planes and artificial limbs, and it’s all down to the way the layers of carbon slot together. Individual layers of graphite are some of the strongest structures in the known universe, but they’re slippery. Each honeycomb sheet of carbon atoms is strong on its own, but the stacks slide around on top of each other forming flakes and faults. In carbon fibres, the arrangement is different. The sheets of graphene aren’t smooth. They form long, thin ribbons that intertwine in random folds, locking…

We used to think that molecules with more than 12 atoms wouldn’t be able to survive in interstellar space, but we were wrong. In 2019, the Hubble Space Telescope confirmed that there are electric buckyballs floating between the stars. These giant molecules contain 60 carbon atoms each, and the telescope revealed that they’re ionised. The energy from nearby stars has pulled away one of their electrons, leaving them with a positive charge. Finding these chunky molecules in outer space could help to answer some puzzling astronomical questions. Scientists have spotted more than 400 strange patterns of light absorption called Diffuse Interstellar Bands, or DIBs, made by unknown molecules in outer space. It could be that complex carbon chemicals are the cause.…

Hydrogen is the most important element there is. It is both dangerous and essential – just two of its amazing qualities. Hydrogen can be found in our bodies and many things around us. Also, hydrogen connects us all to the start of the universe! The special qualities of hydrogen start from its building blocks. In its most familiar form, hydrogen is the simplest element. Its atoms have just one proton and one electron. Like most other elements, it has isotopes with extra neutrons. But hydrogen is the only element with named isotopes. It’s called deuterium when it has one neutron and tritium when it has two. This is more than just a curious fact – our lives rely on hydrogen’s isotopes. That’s because at the heart of the Sun, hydrogen…

Household bleach is a bactericide; it kills bacteria on contact. It’s one of the cheapest and most powerful microbe busters on the planet. But how does it work? The bleach under your sink is a solution of sodium hypochlorite, which has the chemical formula NaClO. That means that each molecule contains one sodium atom, one chlorine atom and one oxygen atom. In water it produces hypochlorous acid (HOCl), which can steal electrons from other molecules. It uses this ability to attack bacteria and viruses, breaking their proteins apart and splitting them open. Hypochlorous acid also damages pigment molecules, turning them white, which is where bleach gets its name from. In its pure form, bleach is extremely corrosive. It has a pH of 13, making it just about as alkaline as…

The Haber process is an efficient way of producing ammonia for use in fertilisers and household products. Ammonia has helped to sustain food production for billions of people, but its use in explosives has reportedly resulted in the death of 150 million. It’s for this reason that some scientists say ammonia changed the course of the 20th century more than electricity or television. Industrial production of ammonia The ins and outs of the Haber process Gas compression The clean hydrogen and nitrogen are mixed and compressed at a pressure of 200 atmospheres. Nitrogen and hydrogen cleaning Before the process can begin, the nitrogen and hydrogen need to be cleaned and purified. Gas recycling The process doesn’t react all the hydrogen and nitrogen together; therefore any leftover gas can be recycled…

Gold represents a tiny fraction of the elements in the known universe. The reason for its rarity is owed to the incomprehensible amount of energy needed for its formation. Gold is formed within stars, but only in those that are exploding in giant supernovae or incredibly dense ones that have come together in monstrously powerful collisions. Stars generate energy through the power of fusion, where smaller elements are fused, or combined together into heavier elements. To start with, a star may be mostly hydrogen, the lightest element. The process of fusion under the immense pressure and heat in the star’s core will generate helium. When hydrogen runs low and the star begins to reach the next phase of its life cycle, it will fuse helium into the next heavier element,…

Plutonium is radioactive, but it doesn’t seem that harmful at first glance. It looks like any other metal, with a silvery sheen that turns dull in contact with the air. Queen Elizabeth II held a piece during a visit to Britain’s Atomic Energy Research Establishment at Harwell in 1957. It was warm to the touch, but it didn’t hurt. Even eating it doesn’t really do any harm, although it’s definitely not recommended. Plutonium atoms fall apart by a process called alpha decay. They release particles made from two neutrons and two protons – essentially a helium nucleus. They’re so bulky that they can’t pass through human skin. Left to its own devices, plutonium decays slowly. The real danger comes when humans interfere. An isotope of plutonium named plutonium-239 is fissile,…

Marie Curie is one of few women to win science’s highest honour, a Nobel Prize, but her work also brought her an early death. She and her husband Pierre spent years carefully grinding radioactive rocks and soaking the powder in acid. In 1898 they discovered the new element polonium, and a few months later, Marie would go on to discover radium too. But the Curies didn’t know how risky their work was. Scientists had discovered radioactivity just a few years earlier. We now know that radioactivity is very dangerous. Worse still, polonium may be the most radioactive element. The danger comes from the building blocks forming elements’ atomic structures. At each atom’s centre is its nucleus. In radioactive elements, the nucleus breaks apart, firing out smaller chunks that can harm people.…

Chemistry is a fascinating subject. The way atoms behave determines everything from the food we eat and the clothes we wear, to our genetic makeup and how we feel. The beautiful simplicity of the periodic table describes just 118 elements that form every known material – 98 if you discount those that can only exist in a laboratory. These elements react in a variety of ways, forming hundreds of millions of compounds – two or more elements bonded together – giving us the diversity of materials that make up our world. Some reactions are physical, not chemical, and the way to tell is whether or not there has been a change in the chemical formula. Melting ice is a physical change because water is the same substance as ice, just…

Gunpowder, unlike other modern explosives, is classified as a low explosive – one that undertakes subsonic combustion – as it deflagrates slowly. For this reason, despite its creation over 1,000 years ago, it was still used as the explosive mechanism in guns up until the 20th century, providing enough energy to propel a bullet out of a muzzle, but not enough to break the weapon and injure the user (of course, backfires and jams lead to bad injuries). Modern rifle cartridges – the combination of a bullet, case, powder and primer – such as the one fired in the accompanying image, use smokeless powders (they are not actually smokeless, however, just considerably less so than conventional black powder), as their combustion efficiency is greatly increased, enabling rounds to be fired with…

When battling blazing wildfires it might seem strange to introduce more fire in an attempt to quash the already-raging flames. However, prescribed burns may help to relieve the painful effects of wildfires. In a strategic endeavour to limit the advancement of wildfires, a human-made wall of fire can be drawn around them in the hopes of starving them of fuel. By purposely burning strips of woodland before wildfires can reach them, a prescribed fire could potentially stop the spread. This isn’t a guarantee, and although controlled by firefighters, there is a risk the prescribed fire could become uncontrollable, or that floating embers could ignite new wildfires.…

Some of the most interesting kitchen chemistry can be observed when baking. Taking four basic ingredients – flour, fat, sugar and eggs – and subtly altering their cooking chemistry can transform them into airy cakes, chewy cookies or flaky pastries. Leavening, or raising, agents introduce bubbles of air. As the air bubbles are heated, the gas that they contain expands, causing cakes, breads and soufflés to rise. These air bubbles can be made in one of two ways. Chemical raising agents, like baking powder and bicarbonate of soda, react with water to form carbon dioxide gas. This reaction occurs very rapidly and the quantity of raising agent must be carefully adjusted – too much and the bubbles will become large and burst, too little and the density of the cake…

Enzymes are often called ‘biological catalysts’, and their job is to speed up chemical reactions. You are full of dissolved chemicals with the potential to come together or separate to form the biological building blocks that you need to stay alive, but the reactions happen too slowly on their own. Enzymes are molecules with ‘active sites’ that lock on to other molecules, bringing them close together so that they can react, or bending their structures so that they can combine or break apart more easily. The enzymes themselves do not actually get involved in the reactions; they just help them to happen faster. Some of the most well-known enzymes are the ones in your digestive system. These are important for breaking down the molecules in your food. However, these aren’t…

Mattifying makeup Mattifying makeup products attempt to minimise shine by including ingredients that absorb oil and water. Clays are made from oxygen or oxygen and hydrogen (hydroxyl groups) and arranged into crystals with four or eight sides. At the centre of each is an atom of silicon or aluminium. These structures form sheets, and it’s between these sheets that oil and water become trapped. Mattifying agents can be found in a variety of products, including powders, foundations, lotions, balms, gels and sprays. Silicone elastomers are a synthetic alternative. They are made from chains of silicone, carbon, hydrogen and oxygen strung together to form branching webs. These expand when liquids are added, helping to lock moisture away. Anti-wrinkle creams Proteins are the major building blocks of the human body and collagen…

In 1994, John Joseph Famalaro was taken in for questioning after a body was discovered in his home. Police investigated his previous addresses, including a warehouse he once owned in Orange County. The place appeared clean, but when luminol was sprayed across the walls, it lit up. The warehouse was covered in blood. After DNA samples had been removed and analysed, it was confirmed that the blood belonged to Denise Huber, who had gone missing three years earlier.…

The Big Bang created the universe roughly 13.8 billion years ago. In the first moments it was so hot and dense that no particles could survive. Whenever quarks and electrons burst into existence, they immediately broke apart. But as the universe expanded and started to cool, these elementary particles became more stable. Then quarks started to come together to form protons and neutrons. Within minutes, these were combining to form the first atomic nuclei. It took another 380,000 years for the universe to cool enough to allow complete hydrogen atoms to form, and then the real magic began to happen. Gravity started to pull the atoms into clumps, and as those clumps grew the pressure inside started to build. The atomic nuclei got so close together that they started to fuse,…

Deoxyribonucleic Acid (DNA) is a chemical library, storing vast quantities of data for billions of years. Passed from one generation to the next, this microscopic structure is the engine of evolution. Every living creature uses DNA as its instruction manual. The genes in DNA tell cells how to make the proteins they need to survive, grow and reproduce. It may be the most famous molecule in the world, but what goes on inside that double helix? At the heart are four chemicals called nucleotides. Each contains a pentagon-shaped sugar molecule, a structure called a phosphate group and a protein fragment called a base. The sugar and the phosphate group are the same for every nucleotide. They join together side by side to form the backbone of each DNA strand. Like…

The sulphur cycle is one of many biochemical processes where a chemical element or compound moves through the biotic and abiotic compartments of the Earth, changing its chemical form along the way. As with the carbon and nitrogen cycles, sulphur moves between the biosphere, atmosphere, hydrosphere and lithosphere (the rigid outer layer of the Earth). In biology, the water, oxygen, nitrogen, carbon, phosphorus and sulphur cycles are of particular interest because they are integral to the cycle of life. Sulphur, present in the amino acids cysteine and methionine as well as the vitamin thiamine, is a vital part of all organic material. Plants get their supply from microorganisms in the soil and water, which convert it into usable organic forms. Animals acquire sulphur by consuming plants and one another. Both…

There are six naturally occurring noble gases found around our world and beyond. These are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). Together they form Group 18 of the periodic table and are characterised by their lack of colour, smell, taste and flammability in their natural state. Despite being historically referred to as rare and inert, noble gases – which were designated ‘noble’ due to their apparent reluctance to undergo a chemical reaction – are nothing of the sort. In fact, all of these gases are found in Earth’s atmosphere and each is capable of being chemically active and producing compounds. The majority of the noble gases – ie argon, krypton, neon and xenon – are formed via liquefaction and fractional distillation techniques, however…

It is widely known that lemons taste sour due to their acid content, soil needs the optimum pH level for plants to grow properly and acid rain can wipe out entire ecosystems. But what really makes one thing acidic and the other one basic (alkaline)? Why can they be so corrosive? And why does litmus paper turn different colours when dipped in acid or a base? Acids and bases can be defined in terms of their concentration of hydrogen ions. Normally an atom of hydrogen consists of one proton and one electron, giving it a balanced electrical charge – protons being positively charged and electrons being negatively charged. Take away the electron and you are left with an ion of hydrogen, or a single proton, or ‘H+’, as it is…

Most young chemists will know litmus paper from science lessons, and older chemists for assessing their home brew. This colour-changing tool is used to find the acidity or alkalinity of a solution – acidic solutions turn the paper red, and alkaline (basic) solutions turn the paper blue. This provides a visual indication of the pH, which is a measure of the concentration of hydrogen ions in a solution. Water molecules can be broken down into positively charged hydrogen ions and negatively charged hydroxide ions. Acidic solutions have higher concentrations of hydrogen ions than hydroxide ions, while the opposite is true of basic solutions. In water and other neutral solutions, the concentration of hydrogen and hydroxide ions is equal. The colour-changing properties of the paper are due to crushed and fermented…

Bleach is an industrial chemical, and it’s produced on an industrial scale. It involves two methods: the chlor-alkali process and the Hooker process. The chlor-alkali process produces the raw materials for bleach production: sodium hydroxide, also known as caustic soda or lye, and chlorine gas. It begins with salty water, also known as brine. The chlor-alkali process uses a technique called electrolysis to break the chemicals in brine apart and remake them into something new. When a current passes through the liquid, it turns water (H2O) and salt (NaCl) into sodium hydroxide (NaOH), chlorine (Cl2) and hydrogen (H2). Two of these three ingredients go on to the next stage, the Hooker process. In the Hooker process, the sodium hydroxide is cooled and the chlorine gas is bubbled through. This produces…

All rainwater is a little bit acidic, because the carbon dioxide present in the atmosphere dissolves in water and forms carbonic acid. Stronger acid rain, however, can damage stone structures and can also be harmful to crops, as well as polluting waterways. It forms in the atmosphere when poisonous gases emitted by human activities combine with the moisture within rain clouds. Fossil-fuelled power stations and petrol/diesel vehicles give off chemical pollutants – mainly sulphur dioxide (SO2) and nitrogen oxides (NOx) – which when mixed with the water in the air react and turn acidic. Acid rain in action 1 Acidic gases Sulphur dioxide and nitrogen oxides from industry and vehicles are released into the atmosphere. 2 Wind The gases are carried on the wind to higher ground, towards rain clouds.…

If you’ve ever been to any kind of stage show, there’s a decent chance you’ll have seen dry ice being used. This is the stuff that’s pumped onto the stage to simulate mist and fog, or generally make the place just look awesome, but what is it and how is it made? Dry ice is actually highly pressurised liquid-carbon dioxide that has been frozen to a temperature of -78.5 degrees Celsius (-109.3 degrees Fahrenheit). The main benefit of using carbon dioxide is that when it warms up it sublimates, which means it changes from solid to gas without becoming a liquid. So if you warm it up and pump it across a stage, it will turn instantly to cool-looking mist, rather than just soaking the floor. It is also really…

You might say that it was hidden in plain sight. Aluminium is a highly reactive metal, meaning it readily undergoes chemical reactions with other elements and compounds to form different substances. As a result, nearly all of the naturally occurring aluminium atoms on Earth ended up tucked away in the molecules of more than 270 different minerals, including gemstones like emeralds and rubies. While it’s actually 8.2 per cent of the Earth’s crust, making it the most common metal and third-most common element, behind oxygen and silicon, you would never know it’s there without investigating on a chemical level. The search was on in the mid-1700s, when chemists began experimenting with alum, a class of abundant chemical compounds. Alum compounds, such as potassium aluminium sulphate, were well known, going back…

We know about bismuth’s unusual beauty because it also melts unusually easily. This metal element turns from solid to liquid at 271 degrees Celsius. That’s much lower than other metals, which melt at thousands of degrees Celsius. As it cools down, highly pure bismuth can form into stepped pyramids and other strange forms. This type of crystal is known as a ‘hopper’. The hopper crystal forms because as it cools, bismuth is driven to rapidly form hard edges in preparation for making a cube-shaped crystal. However, the driving force never lets the faces grow. Instead it impatiently forms more edges, leaving metal spirals that merge into unusual structures. The bare metal can then also react with oxygen in the air, forming a shiny, coloured surface. The low melting point of…

“Alloys are mixtures of elements where at least one of the elements is a metal” If you ever pick up an object made of or containing metal, more often than not it’s an alloy. This underlines the little-known fact that alloys have been vital in making our lives so comfortable. Alloys are mixtures of chemical elements where at least one of the elements is a metal. Unlike the atoms in molecules like water, usually they are not chemically bonded together. Instead they just sit side by side. To mix metal atoms together in this way, someone must melt at least one of the metal components, which usually only happens at very high temperatures. That means alloys can be quite difficult to make – but the effort is worth it. Mixing…

Hydrogen Flammable If one-fifth of the air we breathe wasn’t made up of oxygen, hydrogen might be relatively safe. But hydrogen and oxygen react rapidly, burning together to make water. Caesium Explosive/flammable If you ever come across caesium, handle it with care! Left alone in air, caesium metal bursts into flames. Put in water, it explodes violently. Plutonium Radioactive Plutonium’s atomic structure enables nuclear weapons, and makes it highly radioactive. Being radioactive means that its atoms break down, spitting out chunks that can badly damage human cells. Chromium Carcinogen Chromium metal that has reacted with air is stable and shiny, so is used in car parts. But removing six electrons from a metal chromium atom gives cancer-causing substances. Cadmium Poison A true heavy metal, cadmium can interfere with how calcium…

Explosions are characterised by three factors: a rapid increase in volume, the generation of high temperatures and an extreme release of energy. In addition to this, every explosion generates a shock wave that varies depending on the explosive substance’s detonation velocity. The four main properties of explosions are force, velocity, heat and fragmentation. The force of any explosion is the physical impact it has on its immediate environment, something often increased through a warhead’s shaped charge. An explosion’s force when magnified in a shaped charge can gauge impact craters, tear through the armour of military vehicles and puncture buildings. An explosive’s detonation velocity is the rapidity of the expansion of its volume (gases mainly) post detonation. Typically, the greater the detonation velocity the higher up the relative effectiveness (RE) table the…

Trinitrotoluene This was the first real breakthrough for explosives post-gunpowder. Trinitrotoluene is one of the most commonly used explosives on Earth. It was formed in 1863 and has an RE factor of 1.00. Molecular formula: C6 H2 (NO2 )3 CH3 Dynamite Based on nitroglycerin, dynamite can boast a whopping 60 per cent greater energy density than TNT. It was created in 1867 by the renowned German chemist Alfred Nobel and has an RE factor of 1.50. Molecular formula: C3 H5 N3 O9 C-4 Based on the explosive RDX, C-4 is the most famous plastic explosive used today. It is easily moulded into any shape (excellent for shaped charges) and has a high detonation velocity. It has an RE factor of 1.34. Molecular formula: C3 H6 N6 O6 Semtex Another brand of plastic explosives used mainly in commercial and industrial applications,…

The majority of paints dry through evaporation, a process that allows its pigmentation to be set onto a chosen surface purely by being exposed to the surrounding atmosphere. However, the drying process can vary and is often complicated and altered between different paint types. Paints usually contain three key components: pigments, binders and additives. Pigments are dry, insoluble powders that by wavelength-selective absorption (ie they only reflect certain wavelengths) change the colour of reflected or transmitted light, giving paint its colourisation. They can be ascertained either naturally or produced synthetically. The pigments of paint are given their paint structure by binders, synthetic or natural resins such as acrylics, polyesters or oils that impart adhesion and influence durability and flexibility. Crucially, though, binders can also play a role in how paint…

Ever since our ancestors rubbed two sticks together to produce embers, humans have evolved a fascination with fire. In a relationship which has defined our modern-day selves, fire has transformed the way humans eat, stay warm and build global civilisations. It was described in ancient Greece as one of Earth’s ‘natural elements’ alongside water, air and earth. But what exactly is fire? Fire is an interaction of particles that creates a hot, glowing plasma. Fundamentally, what we see when we strike a match is a series of chemical reactions that emit heat, light, gas and water as byproducts. Every flicker and flare of a dancing flame is created by atoms releasing energy at different stages of being heated. The recipe for fire is relatively simple. Add a dash of oxygen,…

Whether it’s the Fourth of July, Guy Fawkes Night or New Year’s Eve, you’re sure to see the sparking light of nearby fireworks, followed quickly by their boisterous booms. But igniting colourful chemicals and shooting them into the sky isn’t a new tradition by any means. The first fireworks were hurtling into the sky in around 600 BCE in ancient China. Ancient alchemists discovered that mixing potassium nitrate, sulphur and charcoal produced a black powder that’s now referred to as the ‘first gunpowder’. When this powder was stuffed into a bamboo stick and ignited, it created the first firework propulsion system. Early fireworks were used to celebrate weddings, births and even to ward off evil spirits. Modern fireworks still use black powder, but now incorporate small pellets of packed minerals,…

1 Willow As well as coloured salt, a large amount of charcoal is put into the stars of a willow firework. When the stars explode, the charcoal burns in trails as it falls. 2 Palm When larger grains of minerals are used within the shell’s stars, it takes longer for them to combust, creating a palm tree-like effect. 3 Strobe The composition of the compounds used in these dazzling fireworks produces a strobing effect, caused by chemical byproducts of the combustion that re-ignite following the initial explosion. 4 Comet A large amount of charcoal, along with titanium or aluminium, is used to produce long gold and silver tails radiating from a comet firework. 5 Crossette Unlike a typical firework star, the stars of a crossette firework have a four-sided cavity filled…

“Enzymes’ active sites lock on to other molecules, bringing them together to react” Summery Enzymes are biological molecules that bring other molecules together so they can react, but like catalysts they don’t get involved in the reaction themselves.…

Leaving hair unwashed for multiple days can cause it to feel heavy and greasy. This is because the scalp is continuously producing a natural oil called sebum. Without this sebum shield, the proteins within our hair would become damaged more easily. When there is a build-up of this oil and our hair is in need of a wash, water alone can’t remove it very effectively. Sebum largely resists mixing with water, especially if the water is cool, but when the water combines with shampoo it targets the oil. Molecules in shampoo, called surfactants, work to produce a frothy lather. They have two polar ends – one being hydrophobic (repelled by the water) and one being hydrophilic (attracted to the water). When rubbed into hair with both water and oil, the…