Concept atom. Structure of atom and atomic nucleus
Atom is the smallest particle of the element keeping it characteristics.
Atoms of different elements differ from each other. As there are over 100 different elements, there are also over 100 different types of atoms.
Each atom has the kernel located in the center of atom. It contains positively charged particles – protons and the uncharged particles – neutrons.
Electrons, negatively charged particles, rotate around kernels (see Fig. 1-2).
The quantity of protons in the atomic nucleus is called atomic number of the element.
Atomic numbers allow to distinguish one element from another. Each element has atomic weight. Atomic weight is the mass of atom which is defined by the total number of protons and neutrons in the kernel. Electrons practically do not give the contribution to atom lump, the mass of the electron is only 1/1845 part of mass of the proton and it can be neglected.
Electrons rotate on concentric orbits around the kernel. Each orbit is called the cover. These covers are filled in the following sequence: at first the cover To, then L, with M, N, etc. is filled (see Fig. 1-3). The maximum quantity of electrons which can be placed on each cover is shown in Fig. 1-4.
The outer jacket is called valent, and the quantity of electrons which is contained in it is called valency. The farther from the kernel the valent cover, the smaller attraction from the kernel tests each valence electron. Thus, the potential possibility of atom to attach or lose electrons increases if the valent cover is not filled and located rather far from the kernel.
Electrons of the valent cover can receive energy. If these electrons receive enough energy from external forces, they can leave atom and to become the free electrons randomly moving from atom to atom. The materials containing the large number of free electrons are called conductors.
In Fig. 1-5 are compared conductivity of the different metals used as conductors. In the table silver, copper and gold have the valency equal to unit (see Fig. 1-6). However silver is the best conductor as its valence electrons are more weakly connected.
Insulators, contrary to conductors, interfere with electricity course. Insulators are stable thanks to the fact that valence electrons of one atoms join other atoms, filling their valent covers, interfering, thus, with formation of free electrons.
The materials classified as insulators are compared in Fig. 1-7. Mica is the best insulator because it has the smallest number of free electrons on the valent covers.
The intermediate position between conductors and insulators is occupied by semiconductors. Semiconductors are not either good conductors, or good insulators, but they are important because their conductivity can be changed from the conductor to the insulator. Silicon and germaniye are semiconductor materials.
About atom which has identical number of electrons and protons, say that it electrically is neutral. The atom receiving one or more electrons is not electrically neutral. It becomes negatively charged and is called the negatively ionized atom. If atom loses one or more electrons, then it becomes positively charged and is called the positively ionized atom. Process of accession or loss of electrons is called ionization. Ionization plays the large role in course of electric current.Top