Atom consists of extremely dense kernel surrounded with electronic "cloud". The kernel is insignificant a little in comparison with external dimensions of a cloud, and consists of protons and neutrons. Atom in a usual state is neutral, and electrons bear a negative charge. But atom can also draw others electrons, or give the. In that case it will already be a negatively charged or positively charged ion. How to define how many electrons contain in atom?
1. First of all, you will be come to the rescue by Mendeleyev's Table. Having glanced in it, you will see that each chemical element takes not only the strictly certain place, but also individual serial number. For example, at hydrogen it is equal to unit, at carbon – 6, at gold – 79 and so on.
2. Serial number characterizes quantity of protons in a kernel, that is a positive charge of an atomic nucleus. As atom in a usual state is neutral, the positive charge has to be counterbalanced by a negative charge. Therefore, at hydrogen – one electron, carbon – six electrons, at gold – seventy nine electrons.
3. And how to define quantity of electrons in atom if atom, in turn, is a part of any more difficult molecule? For example, what quantity of electrons in atoms of sodium and chlorine if they form a molecule to all of you well-known usual table salt?
4. And there is nothing difficult. Begin with the fact that write a formula of this substance, it will have the following appearance: NaCl. From a formula you will see that the molecule of table salt consists of two elements, namely: alkaline metal of sodium and gas-halogen of chlorine. But it is not neutral atoms of sodium and chlorine, and their ions. Chlorine, forming ionic communication with sodium, thereby "drew" to itself one of its electrons, and, respectively, it "gave" sodium.
5. Again look in Mendeleyev's Table. You will see that sodium has serial number 11, chlorine – 17. Therefore, now the ion of sodium will have 10 electrons, at a chlorine ion – 18.
6. Working on the same algorithm, it is easily possible to define quantity of electrons at any chemical element, whether it be in the form of neutral atom or an ion.