Chemical element

A chemical element is a substance that is made up of only one type of atom. Atoms are made up of protons, neutrons, and electrons.

The number of protons in an atom is called the atomic number. For example, all atoms with 6 protons are atoms of the chemical element carbon, and all atoms with 92 protons are atoms of the element uranium. The number of neutrons in the nucleus does not have to be the same in every atom of an element. Atoms of the same element with different numbers of neutrons are called isotopes. Saying that a substance "contains only one type of atom" really means that it contains only atoms that all have the same number of protons.

The number of protons in the nucleus causes its electric charge. This fixes the number of electrons in its normal (un-ionized) state. The electrons in their atomic orbitals determine the element's various chemical properties.

Elements are the basic building blocks for all types of substances. If a substance contains more than one type of atom, it is a compound or a mixture. The smallest particle of a compound is a molecule.

118 different chemical elements are known to modern chemistry. 92 of these elements can be found in nature, and the others can only be made in laboratories. The human body is made up of 26 elements. The last natural element discovered was uranium, in 1789. The first man-made element was technetium, in 1937.

Chemical elements are commonly arranged in the periodic table. Where the elements are in the table tells us about their properties relative to the other elements.

Chemical symbols

Chemical elements are given a unique chemical symbol. Chemical symbols are used all over the world. This means that, no matter which language is spoken, there is no confusion about what the symbol means. Chemical symbols of elements almost always come from their English or Latin names. For example, carbon has the chemical symbol 'C', and sodium has chemical symbol 'Na', after the Latin natrium. Tungsten is called 'W' after its German name, wolfram.  'Au' is the symbol for gold and it comes from the Latin word for gold, aurum. Another symbol which comes from Latin is 'Ag'. This is the element silver and it comes from the Latin argentum. Lead's symbol, 'Pb', comes from the Latin plumbum and the English word plumber derives from this as pipes used to be made out of lead. Some more recently discovered elements were named after famous people, like einsteinium, which was named after Albert Einstein.

Compounds

Elements can join (react) to form pure compounds (such as water, salts, oxides, and organic compounds). In many cases, these compounds have a fixed composition and their own structure and properties. The properties of the compound may be very different from the elements it is made from. Sodium is a metal that burns when put into water and chlorine is a poisonous gas. When they react together they make sodium chloride (salt) which is generally harmless in small quantities and edible.

Mixtures

Some elements mix together in any proportion to form new structures. Such new structures are not compounds. They are called mixtures or, when the elements are metals, alloys.

 

Base (chemistry)

A base is a substance that can accept a hydrogen ion (H+) from another substance. A chemical can accept a proton if it has a negative charge, or if the molecule has an electronegative atom like oxygen, nitrogen, or chlorine that is rich in electrons. Like acids, some bases are strong and others are weak. The weak bases are less likely to accept protons, while the strong bases quickly take protons in solution or from other molecules. An acid is a base's "chemical opposite". An acid is a substance that will donate a hydrogen atom to the base.

Bases have a pH greater than 7.0. Weak bases generally have a pH value of 7–9 while strong bases have a pH value of 9–14.

How bases work

Bases can be used to neutralize acids. When a base, often OH^–, accepts a proton from an acid, it forms a water molecule which is harmless. When all of the acids and bases react to form water molecules and other neutral salts, it is called neutralization. Acids can also be used to neutralize bases.

Every base has a conjugate acid formed by adding a hydrogen atom to the base. For example, NH₃ (ammonia) is a base and its conjugate acid is the ammonium ion, NH₄⁺. A weak base forms a strong conjugate acid and a strong base forms a weaker conjugate acid. Since ammonia is a moderately strong base, ammonium is a considerably weaker acid.

Characteristics

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Bases have these characteristics:

• Bitter taste (opposed to sour taste of acids)
• Slimy, or soapy feel on fingers (Slippery)
• Many bases react with acids and precipitate salts.
• Strong bases may react violently with acids. An acid spill can be safely neutralised by using a mild base.
• Bases turn red litmus paper blue
• Bases are substances that contain metal oxides or hydroxides
• Bases which are soluble in water form alkalis (soluble bases)

Some common household products are bases. For example, caustic soda and drain cleaner are made from sodium hydroxide, a strong base. Ammonia or an ammonia-based cleaner such as window and glass cleaner, is basic. These stronger bases may cause a skin irritation. Other bases, like cooking ingredients sodium bicarbonate (baking soda) or cream of tartar are basic, but these are not harmful and suitable for cooking.

Gloves should always be worn when handling bases. If skin irritation is encountered, the affected area should be rinsed thoroughly with cold water. If that does not stop the problem, contact medical help as soon as possible.

Strong bases

A strong base is a base that completely converts to hydroxide ions, OH−, in water. Most strong bases are hydroxide salts, which dissolve in water rather than reacting with it.

Sodium hydroxide is the most commonly used strong base, but all salts of alkali metals and alkaline earth metals and the hydroxide ion are strong bases:

• Lithium hydroxide - LiOH
• Sodium hydroxide - NaOH
• Potassium hydroxide - KOH
• Rubidium hydroxide - RbOH
• Cesium hydroxide - CsOH
• Calcium hydroxide - Ca(OH)2
• Strontium hydroxide - Sr(OH)2
• Barium hydroxide - Ba(OH)2

These are sometimes listed as the only strong bases, following the Arrhenius acid-base theory, but this is inaccurate in general. Because of the leveling effect, stronger bases than the hydroxide ion will react with water to produce hydroxide and their conjugate acid. For example, the strong base sodium methoxide reacts to make sodium hydroxide and methanol in water:

NaCH3O + H2O → NaOH + CH3OH

 

Acids and bases

 Acids and bases are common chemicals. Acids release H⁺ ions when in water, and bases release OH⁻ ions when in water. Acids can react with bases. The H⁺ ion is taken from the acid by the base. This makes water, H₂O. A salt is also made when an acid and a base react together. An example would be reacting hydrochloric acid (HCl) and sodium hydroxide (NaOH). Hydrochloric acid releases H⁺ and Cl^- ions in water. The base releases Na⁺ and OH^- ions. The H⁺ and the OH^- react to make water. There is a solution of sodium chloride (NaCl) left. Sodium chloride is a salt.

An acid is a substance that can donate a hydrogen ion (H⁺) (generally speaking, this will be a proton) to another substance. Acids have a pH less than 7.0. A chemical can donate a proton if the hydrogen atom is attached to an electronegative atom like oxygen, nitrogen, or chlorine. Some acids are strong and others are weak. The weak acids hold on to some of their protons, while the strong acids let go of all of them. All acids will release hydrogen ions into solutions. The amount of ions that get released per molecule will determine if the acid is weak or strong. Weak acids are acids that partially release the hydrogen atoms that are attached. These acids, then, may lower pH by dissociation of hydrogen ions, but not completely. Weak acids generally have a pH value of 4-6 while strong acids have a pH value of 1 to 3.

A base is an acid's "chemical opposite." A base is a substance that will accept the acid's hydrogen atom. Bases are molecules that can split apart in water and release hydroxide ions.

Acids can have different strengths, some are more reactive than others. More reactive acids are often more dangerous.

Acids can have a lot of different properties depending on their molecular structure. Most acids have the following properties:

• taste sour when they are eaten
• can sting the skin when they are touched
• can corrode (or eat away at) metals and skin
• can be used as a reactant during electrolysis due to the presence of mobile ions
• turn blue litmus paper red
• turn red or orange on universal indicator
• conduct electricity

Acids can burn the skin, the severity of the burn depending on the type and concentration of the acid. These chemical burns require immediate medical attention.

Because acids donate hydrogen ions, all acids must have hydrogen in them.

Acids can have different strengths, some are more reactive than others. More reactive acids are often more dangerous.

Acids can have a lot of different properties depending on their molecular structure. Most acids have the following properties:

• taste sour when they are eaten
• can sting the skin when they are touched
• can corrode (or eat away at) metals and skin
• can be used as a reactant during electrolysis due to the presence of mobile ions
• turn blue litmus paper red
• turn red or orange on universal indicator
• conduct electricity

Acids can burn the skin, the severity of the burn depending on the type and concentration of the acid. These chemical burns require immediate medical attention.

Because acids donate hydrogen ions, all acids must have hydrogen in them.

One of the biggest diamonds

 The fifth biggest diamond ever discovered has been unearthed in a mine in Lesotho, a small landlocked country surrounded by South Africa. The stone has a weight of 910 carats and the size of two golf balls.

The diamond is especially valuable because it belongs to a category of gems that are colourless and do not have grave impurities.

The diamond was found in the Letseng mine, which in the past has been famous for the size and quality of gems discovered there. Diamonds that come from the Lesotho mine usually sell at a high price. Since 2006 the mine has produced some remarkable diamonds, including the Lesotho Promis, a 603-carat diamond found in 2006.

The newly found diamond will now be cut into smaller stones and polished. After that, diamond traders can actually say how much the diamond is worth, probably around $40 million.

 Gem, the British based company that operates the mine together with the Lesotho government, expects its shares to recover after prices fell and a new mine had to close in Botswana.

The largest diamond ever discovered is still the Cullinan, a 3,106-carat gem found near Pretoria in 1905. It was cut into several stones including the Great Star of Africa, the largest cut diamond in the world. The rest has been cut into the gems that are in the British Crown Jewels.

Words

• British-based = its main headquarters are in the U.K.
• discover = to find for the first time
• colourless = clear, so that you can see through it
• Crown Jewels = objects that are a symbol of the British monarchy, kept in the Tower of London
• especially = above all
• gem = beautiful stone that has been cut into a special shape
• government = people who rule a country
• grave = serious, bad
• impurity = object that is not very pure; with other substances that are mixed into it
• including = also
• landlocked = country that has no coast
• mine = deep hole in the ground that people dig in order to find coal , gold and other metals or minerals
• operate = to run a company; the owner of ...
• polish = to make something smooth, bright and shiny by rubbing it
• recover = here: to go up again
• remarkable = unusual, surprising
• share = part of a company that belongs to an individual
• surrounded = all around it
• trader = person who buys and sells things
• unearth = to dig something up from the earth
• valuable = worth a lot of money
• weight = how heavy something is
• worth = how much money you can get by selling it

 

Have scientists found the Higgs boson?

Scientists in Switzerland have made a major discovery recently. They claim they might have found a Higgs boson, or the “God particle”, as it is sometimes called. Scientists think that the Higgs boson could explain how matter gets its mass or weight. Such a particle is smaller than an atom. Scientists have been searching for this particle for almost 50 years. Without mass, particles wouldn’t hold together. In the 1960s British physicist Peter Higgs predicted that such a particle existed.

Physicists believe that the Higgs boson existed for a very short time after the Big Bang, which led to the creation of the universe about 13 billion years ago. For some time, scientists at the European Center for Nuclear Research, CERN, have been trying to create the energy that existed at that time.

CERN is the home of the Large Hadron Collider, a gigantic machine that produces high energy to smash atoms. Such a machine is used to find out how our universe developed and to look into mysteries we have not yet found an answer to. The LHC lies in a round 26 km long tunnel over a hundred meters below the Earth’s surface.  It sends particles around at light speed.

What physicists call the “standard model” describes the buildings blocks of our universe and the way it works. But there are a few missing links in this theoretical model of physics. One of them is how some particles gain their mass, while others are without mass.

The Higgs theory says that an energy field exists everywhere in the universe. As particles fly around such a field they attract Higgs bosons which are around such fields. Certain particles can attract more Higgs bosons and give them a larger mass, while others attract fewer bosons.

Some scientists are skeptical of their discovery. They say they can’t be 100% sure it is the God particle, but it is different than any other particle they have found so far.

Words

• attract = pull
• billion = a thousand million
• boson = a particle that is smaller than an atom
• certain = here: some
• claim = to say officially that something is true
• collide = crash
• creation = making of
• describe = explain
• develop = grow
• discovery = to find something new
• gain = get
• gigantic = very, very big
• light speed = the distance that light travels in a second = 300,000 km
• major = very important
• mass = weight
• missing link = piece of information that you need in order to explain something
• mystery = something that people cannot understand or explain
• particle = very small part of something
• predict = foresee
• physicist = a person who has special knowledge in physics
• recently = a short time ago
• scientist = a person who is trained in science and works in a laboratory
• skeptical = not sure, doubtful
• smash = break into pieces
• surface = the top part of something

Important Elements

 

Important Elements

Carbon

Carbon is one of the most important elements. All living creatures have carbon in them and the industry uses carbon in many ways.

Carbon’s chemical symbol is C. Its atomic number is 6 and it has a mass of 12, but there are other isotopes of carbon too.

Carbon atoms like to form bonds with other atoms. They can link together with other elements and form very long chains.

A lot of carbon on Earth is found together with other elements. Carbon dioxideis in the air that we breathe out. Minerals, like limestone have carbon in them. Mixtures of carbon and hydrogen are in petroleum and natural gas.

Pure carbon does not occur very often on Earth. The best known forms of pure carbon are diamonds and graphite.

Diamonds are the hardest objects on Earth. They are in the Earth’s crust, formed under high temperatures and pressure. Diamonds are very valuable. Most of them are used in industry—to cut or polish other objects or as drilling heads in oil fields.

 Graphite is a soft grey or black mineral. Like diamonds, graphite is formed under the surface of the Earth. It is used in pencils and, because it is lightweight, you can find it in spaceships, tennis rackets and bicycles.

Chlorine

Chlorine is a poisonous greenish-yellow gas with a strong, bad smell. In nature, it can only be found together with other elements, especially in minerals. Together with sodium it forms salt (NaCl).

Chlorine is used to make water clearer and purer. In swimming pools it kills bacteria. We also use chlorine to clean metal. The industry uses chlorine compounds to produce paper, plastic, medicine and paint.

Chlorine often combines with other elements because it easily accepts free electrons from them. It has 17 protons and an atomic mass of 35.

 Aluminium

Aluminium is a very light silver metal that can be formed into any shape. It is one of the most common elements on Earth. About 8% of the Earth’s crust is made up of aluminium. But you always find it in combination with other elements, never in its pure form.

Aluminium is often used as an alloy—together with copper, magnesium or tin. When it is formed with these elements, aluminium becomes very valuable. Such alloys are very light, but strong. They do not corrode and electricity and heat can pass through them easily.

Aluminium can be as strong as steel. It is very often used to make cars and trucks as well as containers for ships. Industries make cans, pots and pans out of aluminium.

Most of our aluminium is found in rocks called bauxite. About 500 kg of aluminium can be made out of a ton of bauxite. This valuable raw material is mined in tropical and subtropical countries. Australia, Jamaica, Brazil are among the biggest producers.

 Gold

Gold is a shiny, yellow metal , probably one of the most expensive on Earth. It was one of the first metals discovered and people have been using gold for jewellery and coins for thousands of years.

Gold’s chemical symbol is Au (Latin for “aurum”) .It is a soft metal that can be pressed into many different shapes. One ounce of gold (about 30 grams) can be made into a thin wire that is 70 km long.

Gold does not rust when it gets into contact with water or air. Radios and TV sets have parts made of gold because electricity can pass through it well. Dentists use gold to make crowns, because it is easy to shape and gold crowns last a long time. Artists use thin sheets of gold to decorate objects.

Gold can be found in many rocks on Earth. In most cases , gold ore is mined deep under the surface. Sometimes gold is washed away by rain and wind. It gets into rivers where it sinks to the bottom because it is very heavy. In the middle of the 19th century a gold rush broke out all over the world. Gold was discovered in the rivers of Alaska, California and Australia.

Today, South Africa, the USA and Australia are the world’s largest gold-producing countries.

 

Galileo Galilei

Galileo is often called the founder of modern science. He made many discoveries in astronomy and physics and he built telescopes to study space.

Galileo Galilei was born in Pisa, Italy in 1564. His father sent him to the university to study medicine, but young Galileo was more interested in science and mathematics.

Galileo made one of his greatest discoveries as he sat in a cathedral of Pisa. As he watched a chandelier swing back and forth he noticed that longer and shorter swings took the same time. This discovery became known as the law of the pendulum. These and other important discoveries made him so well-known that Galileo became a professor at the University of Pisa.

 Galileo often questioned scientific facts of his age. For a long time people thought that heavier objects fall to Earth faster than lighter ones. By dropping objects of the same size but different weights from the Leaning Tower of Pisa Galileo showed that this wasn’t true.

 In 1609 Galileo constructed his first telescope. He used it to observe the stars and the planets. He saw things that nobody had ever seen before. Galileo discovered that the moon’s surface was not smooth and flat, like everyone thought, but had a rough surface and was full of craters.

In January 1610 Galileo discovered 4 moons revolving around the Jupiter. They were named after him, the Galilean moons. These observations proved that not the Earth was the centre of the solar system, but the sun. It was a discovery that Copernicus had made 60 years earlier.

The Roman Catholic Church did not always like what Galileo taught. It still believed that the Earth was the centre of the universe and everything revolved around it. The church ordered him not to teach such ideas any more.

In 1633 Galileo was brought before the Inquisition, the Church’s court. It sentenced him to life in prison because of his teachings. Galileo was put under house arrest because he was old and not so healthy any more. He spent the last years of his life in Florence, where he continued to work on his theories and even published a final book. He became blind and died in 1642.

In 1992 Pope John Paul II published a document that said the Church made a mistake by condemning Galileo.