Structure of the Atom
Atoms are very small and cannot be seen with the naked eye nor can they be seen in microscopes using the eye. One million atoms fit across the width of a strand of hair.
They consist of two main parts: the positively charged nucleus at the centre and the negatively charged elementary particles called electrons which surround the nucleus in their orbitals. (Elementary particle means that the electron cannot be broken down to anything smaller and can be thought of as a point particle.) The nucleus of an atom is made up of a collection of positively charged protons and neutral particles called neutrons.
Interesting fact: the neutrons and protons are not elementary particles. They are actually made up of even smaller particles called quarks. Both protons and neutrons are made of three quarks each. There are all sorts of other particles composed of quarks which nuclear physicists study using huge detectors - you can find out more about this by reading the essay in Chapter ??
NOTE :Insert diagram of atomic structure - see lab posters
Atoms are electrically neutral which means that they have the same number of negative electrons as positive protons. The number of protons in an atom is called the atomic number which is sometimes also called Z.
NOTE :check A and Z
The atomic number is what distinguishes the different chemical elements in the Periodic table from each other. In fact, the elements are listed on the Periodic table in order of their atomic numbers. For example, the first element, hydrogen (H), has one proton whereas the sixth element, carbon (C) has 6 protons. Atoms with the same number of protons (atomic number) share physical properties and show similar chemical behaviour. The number of neutrons plus protons in the nucleus is called the atomic mass of the atom.