Science
Chemistry
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Acids and bases
Many acids and bases are highly reactive chemicals: they easily combine with other substances in chemical reactions to form new ones. Most bases do not dissolve in water; those...
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Atoms
All matter is made of atoms. An individual atom is far too small to see other than with the most powerful microscopes. But atoms joined together make up every solid object...
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Carbon
One of the most important chemical elements is carbon: it is the fourth most common element in the Universe. Carbon is the main element in all living things. It makes up one-fifth...
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Carbon dioxide
Carbon dioxide (chemical formula CO2) is a colourless gas. It consists of a carbon atom covalently bonded to two oxygen atoms. It is about 60% denser than air. CO2 is soluble in...
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Chemical analysis
Chemical analysis is the study of the chemical composition and structure of substances. It is split into two areas. Qualitative analysis aims to discover the elements or compounds...
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Chemical reactions
A chemical reaction takes place when two or more different substances join together to form one or more new substances. The change involves the movement of electrons in both the...
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Chemistry A-Z
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Crystals
In many solid substances, the atoms or molecules are fixed in place but they are not positioned at random. They are arranged in an orderly or regular pattern known as a crystalline...
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Density
Density is the amount of matter in a certain place or volume. The more matter within a certain volume, the denser the substance or object and the greater its mass. Some objects are...
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Electrolysis
Electricity can be used to separate a chemical compound into the molecules that make it up. This process is called electrolysis. For it to work, the compound has to conduct...
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Elements and their uses
An element is a substance made up of atoms of the same type. It cannot be broken down into simpler substances. Different elements have different characteristics, which are...
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Hydrogen
Hydrogen is a colourless, odourless, tasteless, non-toxic, highly combustible gas. The most abundant element in the Universe, it forms the bulk of most stars. On Earth, most...
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Kinetic theory
All matter is made up of molecules or atoms that are in constant motion. This view of the way matter behaves is called kinetic theory ("kinetic" means moving). Ever since the 17th...
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Matter
Everything is made of matter. Every object, substance, chemical and material is matter. This includes not only things you can see easily, but also specks of dust too small to...
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Methane
Methane is a colourless, odourless, flammable gas. It is a compound with the chemical formula CH4 (one atom of carbon and four atoms of hydrogen). It is the main ingredient of...
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Molecules
Atoms make up all the objects and substances in our world. But they rarely exist as single atoms, alone or unattached. They are usually attached or joined to other atoms. For...
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Oxidation and reduction
Lighting a fire, iron rusting and even our own breathing are all examples of a kind of chemical reaction called oxidation. Substances that gain oxygen or lose hydrogen atoms are...
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Oxygen
Oxygen is one of the commonest chemical elements on Earth. It forms about half the weight of the planet’s hard outer rock layer or crust, as it is found in most minerals...
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Periodic Table
The Periodic Table of elements is a list of all known elements arranged in order of their atomic numbers (the number of protons in each atom). It was designed by Russian scientist...
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Properties of matter
Matter exists as a solid, a liquid or a gas. It is made up of atoms of certain types (elements), either of just one type or a combination of two or more. Different materials have...
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Radioactivity
Most atoms are stable. They remain the same through time. Others are unstable—they are likely to break up. This is because they do not have enough energy to bind the nucleus...
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Solutions
Stir a teaspoon of table salt into a glass of water—and the salt disappears. However, tasting the water shows the salt is still there. It has dissolved. The large grains or...
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Subatomic particles
An atom is the smallest part of an element. But an atom is not the smallest thing there is. Inside it are even smaller, subatomic particles. Most of these cluster together in the...
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Water
Water is a molecule with the chemical formula H2O. It contains two chemical elements—hydrogen (H) and oxygen (O)—with each atom of oxygen bonded to two hydrogen atoms. Water...
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What is a flame?
We are all familiar with flames, the flickering tongues of coloured light that ripple upwards from bonfires and burning candles. Flames are the visible portion of hot gases that...
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What makes some drinks fizzy?
The fizz in a drink is caused by a mass of tiny bubbles rising up through the liquid. These bubbles contain gas that was dissolved in the liquid, but is now escaping. The gas is...
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Why do cakes rise when they are baked?
To make a cake, you add bicarbonate of soda to the cake mixture. It reacts with acidic ingredients, such as lemon juice, milk, honey or brown sugar, that are also in the mixture...
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