What is an Electron?
An electron is a subatomic particle which is electrically negative in charge. Electrons are found in every atom apart from other particles. Electrons are the primary element of electric current. Charge on one electron is known as a unit electrical charge. The charge of an electron is equal to the charge of the proton hole with an opposite sign. The amount of electrical charge is not determined according to each electron’s since it is extremely small. Instead of that, it is determined by the standard unit of quantity of electrical charge and represented by the coulomb (C).
C = 6.24 x 1018 electrons
The mass of an electron at rest is approximately 9.11 x 10-31 kilogram (kg) and represented by “me” and charge is 1.602 × 10-19 coulombs symbolized as “e”.
The existence of charged particles was first discussed or hypothesized by Richard Laming (1838-1851). Later, Irish physicist G. Johnstone Stoney suggested the term “electron” for the particle in the year 1891. The electron was finally discovered or identified as a particle by British physicist J.J. Thomson and his team in the year 1897.
Meanwhile, an atom is the smallest possible component of an element. Every solid, liquid, gas and plasma are composed of atoms. Atoms are extremely small; typical sizes are around 100 picometers. Atoms are very small that it is not possible to predict accurately the behaviour of an atom. An atom also comprises of neutrons and protons. Protons are positively charged while neutrons neither have a positive charge nor a negative charge. It is a chargeless particle.
Also Read: Atomic Structure
The centre most part of an atom is called its nucleus. The proton and neutron are housed inside the nucleus of the atom. Electrons, on the other hand, are found outside of the nucleus.
The electrons of an atom are attracted to the protons in the nucleus of the atom. If the number of electrons is equal to the number of neutrons, then the atom is electrically neutral. If an atom has more or fewer number of electrons than the number of protons, then it has an overall negative or positive charge, respectively. These atoms are called ions.
Electrons have an electric charge of −1 and their mass is approximately about 1/2000 the mass of a neutron or proton. Electrons are an important part of numerous physical phenomena including magnetism, electricity, thermal conductivity, etc.
Electron Shell (Orbitals)
An atom consists of a number of shells around its nucleus. These shells accommodate the electrons of the atom. Electron shells usually consist of one or more subshells. The electron shell decides the electronic configuration of the atom. The number of electrons that can be accommodated in each shell is given by 2n2 where n is the number of the electron shell.
First electron shell can accommodate only 2 electrons and as the shell number increases the number of electrons that can be accommodated increases. This orbital filled first before the next orbitals.
1. Hydrogen has 1 electron, electronic configuration of hydrogen – 1s1.
2. Helium has 2 electrons, electronic configuration of Helium – 1s2.
Second electron shell contains one spherical shape s orbital and three dumble shape p orbitals, each can accommodate 2 electrons. After the first electro shell filling of 1s orbital, 2s and 2p orbitals of second electron shells are filled in.
- The atomic number of Li is 3, the electronic configuration of Lithium = 1s2 2s1.
- The atomic number of Ne is 10, the electronic configuration of Neon = 1s2 2s2 2p6 (Inert gas).
Third electron shell includes additional orbitals for large elements. Subshell d accommodates 5 orbitals and subshell f accommodates 7 orbitals.
The 3n principal shell has orbitals of s p and d and can accommodate 18 electrons in it and 4n principal shell has s,p,d and f subshell and can accommodate 34 electrons in it.
The electrons in the outermost occupied shell determine the chemical properties of the atom; it is called the valence shell and the electrons in the valence shell are called the valence electrons.
Each shell consists of one or more subshells, and each subshell consists of one or more atomic orbitals.
The electron shells are labelled as K, L, M, N, O, P, Q or 1, 2, 3, 4, 5, 6, 7 going from innermost electron shell to the outermost shell. The electrons in the outer shell occupy higher average energy and these electrons can move farther than that of electrons in the innermost shell. The pull of the atom’s nucleus on the valence electrons will be less and can easily be broken. The pull of the nucleus reduces as the shell number increases and therefore by giving a small external force the electrons can be moved out of the shell.
There are some energy bands and energy gaps in an atom. Each electron is located or included in any of the energy bands. Each atom has a valence band and a conduction band. The gap between the valence band and the conduction band is called the forbidden energy gap. The gap also decides the electrical properties of the material.
The outermost electrons are placed in the valence band. The electrons in the conduction band can move freely to produce electricity.
For a conductor, the conduction band overlaps the valence band and without any further energy, the electrons in the valence band can be brought to the conduction band. No forbidden gap is found in conductors. The common examples of conductors are copper, silver, etc.
For a semiconductor, the gap between the valence band and the conduction band is very small. A semi-conductor has a forbidden energy gap of approximately 1 electron volt(1 eV). The electrons in the valence band of a semiconductor can be moved to the conduction band by applying an external force. At normal temperature, semi-conductor acts as insulators. By applying an external force greater than 1 electron volt, semi-conductor can be made as a conductor. The common examples of semi-conductors are germanium and silicon.
Read More: Semi-conductors
For insulators, the gap between the valence band and the conduction band is very large. Insulators have a forbidden energy gap of approximately 15 electron volt (15 eV). The electrons in the valence band of an insulator can not be moved to the conduction band and hence insulators remain as insulators itself. The common examples of insulators are rubber, wood, plastic etc.
An electron cloud is an atomic model in which the atom consists of a small nucleus surrounded by a cloud of fast-moving electrons. In an electron cloud, it is not possible to find the exact position of an electron at any given time. Electron cloud model predicts the probability of density of electron around the nucleus of the atom.
Positrons are identical to electrons. What makes positrons different from electrons is that it carries charges of opposite sign. When a positron collides with an electron, both particles may be destroyed producing gamma-ray photons.
Electron diffraction is the wave nature of electrons. This is utilised for analysing the crystal structure of the matter in high accuracy.
The electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.
The strongest bonds are usually formed by electrons in an atom. An electron further helps to maintain a chemical bond between two different atoms. Nonetheless, a chemical bond is a lasting attraction between atoms or molecules that results in the formation of chemical compounds. There are three main types of chemical bonds. They are;
- Covalent bond
- Ionic bond
- Metallic bond
Covalent bonds are formed by the equal sharing of electrons between two or more atoms. By covalent bonding of atoms, new molecules are formed. The most common example of covalent bonding is H2O.
Properties of covalent bond compounds:
1. Lower melting and boiling point compared to ionic compounds.
2. Covalent compounds are flexible compounds, not hard compounds.
3. Less flammable and does not conduct electricity in the water.
4. Does not soluble in water.
Ionic bonding is the transfer of valence electrons from one atom to another. In ionic bonding, the metal loses electrons to become positively charged cation and non-metals accept those electrons to become negatively charged anion.
Lithium Fluoride (LiF) is an example of an ionic bond
Properties of Ionic compounds
1. High melting and boiling point compared to covalent compounds.
2. They are hard compounds.
3. More flammable and conduct electricity in the water.
4. Soluble in water.
Metallic bonding is a type of chemical bond formed between positively charged atoms in which the free electrons are shared among a lattice of cations. The covalent and ionic bonds form between two discrete atoms while Metallic bonding forms between same metal atoms. Iron and cobalt are examples of metallic bonding.
Read More: Chemical Bonding
- Electron beams are used in different fields such as in welding, treatment of tumours, electron beam lithography, electron beam processing.
- Low Energy Electron Diffraction
- Free electron laser
- Cathode Ray tubes and Vaccum tubes