Английский язык: Аннотирование и реферирование текста

251 There are more than one hundred different atoms or elements. The simplest and lightest is Hydrogen. An atom of Hydrogen consists of one electron whirling around one proton much like the moon revolv- ing around the earth. The next atom in terms of weight is Helium (He) consisting two protons and two electrons. The third atom is Lithium (Li) with three protons and three electrons and so it goes on. Some of the elements and their atomic weights are: Hydrogen (1); Helium (2); Lithium (3); Carbon (6); Oxygen (8); Aluminium (13); Silicon (14); Iron (26); Nickel (28); Copper (29); Germanium (32); Gold (79); Lead (82). Most atoms have a nucleus consisting of all the protons of the atom and also one or more neutrons. The remainder of the electrons (always equal in number to the nuclear protons) are whirling around the nucleus in different layers. The first layer of electrons outside the nu- cleus can only accomodate two electrons. If the atom has three elec- trons then two will be in the first layer and the third will be in the next layer. The second layer is completely filled when eight electrons are whirling around it. The third is filled when eighteen electrons are whirl- ing around. Don't think these electrons whirl around in some haphazard man- ner, they don't. The electrons in an element of a large atomic number are grouped into rings having a definite number of electrons. The only atoms in which these rings are completely filled are those of inert gase- ous elements such as Helium, Neon, Argon, Krypton, Xenon and Radon. All the other elements have one or more uncompleted rings of electrons. Some of the electrons in the outer orbit of atoms such as copper or silver can be easily dislodged. These electrons travel out into the wide open spaces between the atoms and molecules and may be termed free electrons. It is the ability of these electrons to drift from atom to atom which makes electric current possible. Other electrons will resist dislodgement and are called bound electrons.