ELECTRONS

All matter, both living and nonliving, is composed of basic structures called elements. There are only 92 naturally occurring elements. Elements are what they are because they cannot be broken down to substances with different properties. Elements contain tiny particles called atoms. There is only one type of atom in each type of element. The three most stable parts of an atom are the proton, neutron and electrons. Protons and neutrons are located with the nucleus of an atom. Electrons move around the atom. Most of an atom is empty space. Protons and electrons carry an electrical charge; protons have a positive electrical charge and neutrons have a negative electrical charge. When an atom is electrically neutral, the number of protons equals the number of electrons. The entire atom is held together by the electrical force between the positive nucleus and the negative electrons. The periodic table is a convenient listing of the 92 naturally occurring elements. The element’s atomic symbol, weight and number are included on this chart. One or two letters of each element is used to create it’s atomic symbol. An element’s atomic number is the number of protons in each atom of the element. The atomic weight of an element is the weight of each individual atom’s protons and neutrons. Atoms are listed according to increasing atomic number on the periodic table of elements. The rows are arranged according to the number of electrons in the outer shell. Electrons orbit the nucleus of the atom at fixed distances, forming electron shells that correspond to different energy levels. The electron shell closest to the atomic nucleus is the smallest and can hold only 2 electrons. The second shell can hold up to eight electrons.