My Science School

               Matter exists in three states: solid, liquid and gas. The molecules in all matter are in constant motion, and in a gas they are held together so loosely that they can move freely. Gas molecules move about rapidly and at random. This means that a gas will expand to fill any space it occupies. The molecules in a gas press against anything that restrains them, causing pressure. As a gas is heated, the molecules move further apart and move about more rapidly. If it is restricted in a container, the pressure will increase. If any gas is cooled sufficiently, it will condense into a liquid. This is why some of the outer planets of the solar system are composed of liquid methane and hydrogen.

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               Radioactivity can contain large amounts of energy, which causes damage to matter, including living cells. These forms of radioactivity can knock electrons out of the atoms of a substance to produce ions, which have different properties.

               Organic compounds always contain the element carbon. Carbon compounds often have a very complicated structure, and they are responsible for most of the chemical reactions that sustain life. Carbon is found in some very large molecules, such as those in proteins and plastics. It has proved relatively easy to manufacture many of these substances artificially.

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               New elements are created by bombarding other elements with radiation in an atomic reactor. Scientists have made 16 artificial elements by bombarding uranium and other radioactive elements.

 

               Radioactivity is a form of energy given off by some types of atom with a high atomic number, such as uranium, radium and plutonium. Some forms of radiation consist of protons and neutrons bound together, while other forms consist of electrons or other particles called positrons. As radiation is emitted, the loss of particles from the original atoms changes their properties to those of another atom with a lower atomic number.

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Hydrogen is the lightest and simplest element, and its atomic number is 1. Uranium is the heaviest and its atomic number is 92 — indicating that it has 92 protons in each atom.

 

 

 

 

 

 

 

 

 

 

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           The periodic table is a list of all the elements, arranged in such a way that elements with similar properties are grouped together. Each element in the table is given a number, called an atomic number, which indicates the number of protons the atom has. (A single atom has the same number of protons as electrons.) Elements with the same number of electrons in their outer shells are grouped together in the table.

How many different elements are there?

               There are 92 elements that exist naturally, but it has been possible for scientists to create many more in the laboratory. These artificial elements are radioactive and they quickly decay or lose their radioactivity. Some exist for only a few seconds or less.

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               Antimatter is like normal matter, but it is made up of particles that are exactly the opposite to those making up ordinary matter. A normal electron, for example, has a negative charge, but in anti-matter, the corresponding particle has a positive charge. Antimatter was first proposed in 1930, and it is now possible to make it in tiny amounts, using a machine called a particle accelerator. When antimatter and normal matter make contact, huge amounts of energy are released.

 

 

 

               

Niels Bohr, a Danish physicist, was awarded the Nobel Prize in 1922 for his discovery of the structure of the atom. He went on to help develop the atomic bomb in 1943.

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               The smallest part of a substance that can exist on its own is a molecule. This consists of anything between two and several thousand atoms, which are linked together by chemical bonds. Sometimes the molecule consists of identical atoms, and it is called an element. When a group of different types of atom is connected together in this way, it forms a compound.

               The way in which the atoms become linked depends on the types of chemical bonds. This, in turn, determines the shape the molecule and its chemical properties.

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               Quantum mechanics helps us to understand how energy is used or released by atoms. Negatively charged electrons circle about the positively charged nucleus of the atom. They stay in the same orbit, until this is disturbed, and each orbit has its own level of energy. If more energy is added, when the atom is heated or when light shines on it, the electron jumps out to another orbit, absorbing the extra energy. Then when it drops back again to its original orbit, it releases this energy as heat or light. This tiny packet of energy is called a quantum. Heisenberg’s Uncertainty Principle states that it is not possible to measure exactly where a subatomic particle is and how fast it is moving, because any attempt to measure it will disturb the particle and change its characteristics.

               Atoms consist almost entirely of empty space, because almost all their mass is concentrated into the nucleus. If an atom were enlarged to the size of a football, its nucleus would still be too small for you to see it with the naked eye.

What are electrons?

               Electrons are the very tiny particles that travel around the nucleus of an atom at incredibly high speed. They carry a negative electrical charge.

               The circling electrons are arranged in different layers called shells. If there are many electrons circling around the atom and the outer shell is full, the atom will not react with other substances. If the outer shell is not full, the atom can gain or lose its electrons as it reacts chemically with other atoms around it.

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               The centre of an atom is its nucleus, which has shells of electrons hurtling around it. The nucleus consists of protons, which are electrically charged particles, and neutrons, which have no electrical charge at all. The nuclei of similar atoms usually contain the same numbers of electrons and protons, but sometimes the number of neutrons varies. These atoms with different numbers of neutrons are known as isotopes.

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               There are many smaller particles, and more are being discovered. These very small particles are known as subatomic particles. The electron revolving around the atom, and the neutron and the proton that make up the nucleus, are all subatomic particles.

               Another type of subatomic particle is the positron. It is the same as an electron but with a positive electrical charge. If a positron collides with an electron they are both destroyed and form a shower of even smaller particles. Even neutrons and protons are thought to consist of even smaller particles, called quarks. Photons, gluons and bosons are other forms of subatomic particles, and there may be as many as 100 different types altogether.

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               Atoms are the smallest pieces of matter. They are the tiniest particles into which a substance can be divided without changing into something else. Atoms actually consist almost entirely of open space, in which tiny particles orbit the central particle, or nucleus. The particles travel so fast that they seem to be solid.

               Atoms are so tiny that the smallest particle visible to the naked eye would contain about one million billion atoms. Despite their tiny size, atoms can be seen individually under very powerful electron microscopes.

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