Category Science

           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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