All of the protons and neutrons are sure along into a compact nucleus. Nucleus might be thought of as a central sun, concerning that electrons revolve in a specific fashion. This structure encompassing the nucleus is referred because the lepton cloud.
In the traditional atom the amount of protons equal to the amount of electrons. Associate degree atom as a whole is electrically neutral. The electrons are organized in totally different orbits. The nucleus exert a force of attraction on the revolving electrons and hold them along. All these totally different orbits are preferred to as shells and possess bound energy. Thus this are conjointly referred to as energy shells or quanta. The orbit that is highest to the nucleus is often underneath the tremendous force of attraction whereas the orbit that is farthest from the nucleus is underneath terribly weak force of attraction.
In certain atoms such valence electrons are so loosely sure to the nucleus that at temperature the further energy imparted to the valence electrons causes them to flee from the shell and exist as free electrons. Such free electrons are primarily accountable for the flow of electrical current through metals.
The electrons that are revolving spherical the nucleus, not revolve in a single orbit every orbit consists of fastened variety of electrons. In general, associate degree orbit will contain a most of 2n2. So first orbit occupy maximum of 2x12 electrons ie. two electrons while the second shell can occupy maximum of 2x22 ie. 8 electrons and so on. The exception to this rule is that the valence shell can occupy maximum 8 electrons irrespective of its number.
Let us see the structure of 2 totally different atoms.
1) Hydrogen: This atom consists of 1 nucleon and one lepton revolving around the nucleus. This is that the simplest atom. This can be shown within the Figure. (a). The dot represents associate degree lepton whereas nucleus is diagrammatic by a circle with the positive sign within it.
2) Silicon: This atom consists of fourteen electrons. These revolve around the nucleus in 3 orbits. The 1st 'orbit has most a pair of electrons, the second has most eight electrons and therefore the third orbit has remaining four electrons.
The four electrons set in the farthest shell are loosely control by the nucleus and customarily on the market as free electrons. If by any suggests that some of the electrons are removed, the negative charge of that atom decreases whereas completely charged protons stay same. The resultant' charge on the atom remains a lot of positive in nature and such part is termed completely charged. whereas if by any suggests that the electrons are side, then the total negative charge will increase than positive and such part is termed negatively charged.
Definition of Electron: The electrons re revolving in farthest orbit are hence loosely held to the nucleus. Such a shell is called the valence cell and such electron is called valence electron.