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<h2>Atoms</h2> <p><b>What is an atom made of?</b></p> <p>Although in nature atoms are the basic building block, atoms themselves are made of pieces. Those pieces are called sub-atomic particles, because they are smaller than atoms. Atoms are made up of three particles: protons which have a positive electrical charge, electrons which have a negative electrical charge and neutrons which carry no charge.</p> <p>In the centre of each atom is a nucleus which contains protons and neutrons. Surrounding the nucleus at a distance are electrons. The nucleus is ten thousand times smaller in diameter than the total atom size, so most of the atom is empty space. Protons and neutrons are about the same size as each other, but electrons are 1800 times smaller.</p> <p>Different numbers of these subatomic particles make atoms of different elements. If an atom has a single proton in the nucleus it is hydrogen. If there are two protons in an atom's nucleus it is helium. Three protons makes lithium, four make beryllium, and so on upwards. 82 protons make an atom of lead and beyond that are the very heavy elements. The heaviest atom that we know of so far has 118 protons. The number of protons in the nucleus of an atom defines what element that atom is and how it behaves.</p> <p>Because protons are positively charged, and electrons are negatively charged an atom is electrically uncharged if there is an even number of electrons and protons to cancel each other out. A regular atom of oxygen for instance will have eight protons in the nucleus and eight electrons surrounding it. Atoms that do not have the same number of protons and electrons are called ions. An ion is just an atom with an electrical charge. It will be attracted to ions with opposite charge.</p> <p>An ion is not fundamentally different from a 'normal' uncharged atom. An atom's fundamental nature depends only on the number of protons in its nucleus. A regular oxygen atom has 8 protons and 8 electrons. An oxygen with 9 electrons is a negative ion, one with 7 electrons is a positive ion. But an atom with 9 protons and 7 electrons isn't oxygen any more, it is fluorine. Ions with opposite charges will combine together easily into molecules, that process is a chemical process.</p> <p>The third sub-atomic particle was the last to be discovered because it is uncharged and therefore difficult to detect. It was not until 1932 in fact that Chadwick proposed the existence of the neutron as a result of his experiments. The nucleus of an atom is made up of roughly equal numbers of protons and neutrons.</p> <p> <a href="basics2.html" target="_top">next ></a></p>
