It is well known to us that an atom consists of protons, neutrons, and electrons. The central mass of an atom is made up of protons and neutrons and electrons revolve in orbitals. The number and arrangement of protons, neutrons and electrons in an atom determine the physical, chemical and electrical properties of an element. The numbers and arrangements of protons, neutrons and electrons in an atom are collectively called structure of an atom of the element. The structure is alternatively called atomic structure.
The atomic structure of carbon and copper are not same and this is the reason the properties of carbon and copper are different. Let us examine the structure of a copper atom. It has 29 electrons. The first orbit consists of two electrons, the second orbit consists of 8 electrons and the third orbit consists of 18 electrons. The fourth or outermost orbit consists of 29 – 28 or 1 electron. The electron is most important to study in detail because electronics engineering is based on the different behaviour of electrons.
An electron is negatively charged very tiny and nearly massless particle. The electric charge of an electron is 1.602 × 10 – 19 coulombs. The mass of an electron is 9 × 10 – 31 kg. The charge to mass ratio of an electron is 1.602 × 10 – 19/9 × 10 – 31 or 1.71 × 10 11 coloumb/kg. This ratio proves that the charge of an electron is significantly high compared to its mass. This causes the electron extremely mobile and it is greatly influenced by electric field and magnetic field.
There are two types of energy associated with an electron moving around the nucleus of an atom. One is kinetic energy due to the motion of the electron. Other is potential energy due to the charge of the electron as well as the charge of the nucleus. The total energy associated with an electron is the sum of these two energies. The energy of an electron is more in outer orbit than that of an electron in inner orbit. So this is clear that the electrons moving in the outermost orbit posses the highest level of energy. This is why, the electrons in the last orbit or outermost orbit play a vital role in signifying physical, chemical and obviously electrical properties of an element.
It is well known to us that the outermost shell of an atom processes maximum 8 number of electrons. So the maximum number of valence electrons of an atom cannot be more than 8. In this article, we will concentrate on the electrical properties of an element and try to observe how the electrical property is determined by the number of valence electrons in the outermost shell.
Electrical Conductivity and Valence Electrons
By electrical conductivity, the elements are divided into three groups.
All metallic substances are the good conductor of electricity. If we observe the electronic configuration of any metal element we will find that it has less than 4 electrons in its outermost shell that means it has less than four valence electrons. Most commonly used electrical conducting material is aluminium and it has three valence electrons, and another metallic conductor is magnesium which has two valence electrons. The most popularly known electrical conductor is copper, and the copper atom has only one valence electron.
When the number of valence electrons in an element is 4, the element will have the properties of purely metallic only non-metallic elements. The properties of such elements and materials are in between metallic and nonmetallic. The elements or materials can not conduct electric current as efficiently as a conductor and at the same time, they cannot block the flow of current through them. The conductivity of these elements which have four valence electrons is moderate that is not good as well as not bad. These elements or materials are called semiconductor. Carbon, silicon and germanium are semiconductor elements, and these have precisely four valence electrons in their atoms.
When the number of valence electrons in the atom is more than four, the element behaves as non-metal. The non-metal is a bad conductor of electricity. These elements and the materials made of those elements are called insulator or insulation materials. The three well-known examples of the insulator are nitrogen, sulphur and neon.
- Nitrogen has 5 valence electrons
- Sulphur has 6 valence electrons
- Neon has 8 Valence electrons.
Electrons of all elements do not process the same level of energy. The energy of valence electrons is more in metallic element than that in the non-metallic element. If a valence electron possesses high energy, it is closely associated with its parent atom. The slight influence of an external force can easily detach the electron from its orbit. These loosely attached or detached electrons can freely move into the metallic crystal with random motion. These freely and randomly moving valence electrons are called free electrons. The movement of these separated free electrons towards a particular direction causes an electric current in a conductor. Hence, the electrical conductivity of a material depends upon the behaviour of free-electrons in it.
The metallic conductors do have plenty of free electrons in its crystal even at room temperature. When we apply a potential difference across the conductor due to the electrostatic force or due to the influence of electric field the free electrons move towards the positive side of the applied potential. The movement of free-electrons with their localised random motion causes an electric current in the conductor.
A pure and ideal insulator does not have any free electron at room temperature hence it does not allow electric current to flow through it. In other words, due to lack of free electrons in an insulator, there would not be any current developed in it when we apply a potential difference across the insulator.