When you are going to start learning the subject Electronics devices, At first sight you need to understand some key concepts and definitions which are explained below.
Matter: Matter is defined as anything that has weight and can occupy space.
e.g. our own body, air, water etc. and matter can be found in any one of the three states: Solid, Liquid and Gaseous.
Element: A substance which can not be reduced to a simpler substance by chemical reaction.
e.g. copper, gold, silver.
Compound: When two or more elements are combined chemically then the new substance formed is called as compound. Compound can be separated by chemical but not physical means.
e.g. salt, water.
Atom: An Atom is the smallest individual particle of an element which retains the characteristics of that element. These atoms of each elements are made up of Electrons, Protons and Neutrons.
Electron is having small negative charge of electricity. Proton has positive charge of electricity which is equal and opposite to the charge of Electron. Neutron has no electric charge.
Electrons, Protons and Neutrons are arranged like a solar system. Protons and Neutrons are at the center and they form a heavy nucleus having positive charge and Electrons revolve around them.
Atomic Number: The number of protons in the nucleus gives the atomic number.
Below figure shows the atomic structure of Silicon atom.
From above fig. atomic number of Silicon is 14. In this fig. shown the black circles are called as shells. The number of electrons required to fill the shells is given by Pauli's Exclusion Principle it states that each shell will contain maximum of 2(n^2) number of electrons where n is shell number starting from 1. By this principle first shell consist of 2(1^2) that is max 2 electrons, second shell consist of 2(2^2) that is max 8 electrons, third shell will consist of max 2(3^2) that is 18 electrons and so on.
Valence: The number of electrons in the outermost shell gives the Valence of that atom. For this reason the outermost shell of an atom is called as Valence shell and the electrons in this shell are called as valence electrons. The valence shell can either gain or lose electrons depending upon the number of electrons.
Ionization: When an atom gains or lose electrons in this process it is said to Ionized. When an atom gains electrons then it becomes more negative and is called Negative ION. When an atom loses electrons then it will be having less number of electrons than previous and it becomes a Positive ION.
