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Electrons were discovered as a result of a study of cathode rays by JJ Thomson. It carries a negative charge ( 1.6 X 10-19 C). The name electricity is taken from the Greek word electron, meaning amber. Many pairs of materials which on rubbing could attract light objects like straw, pith balls, and bits of paper. It was found that if two glass rods rubbed with wool or silk cloth when brought close to each other, they repel. The two strands of wool and two pieces of silk cloth, with which the rods were rubbed, also repel each other. But, the glass rod and wool attracted each other.
Electrons
Electrons are negatively charged subatomic particles present inside the atom. For an electric current electron, it plays the role of primary element. The charge of an electron is equal to the charge of a proton.
Charge
A charge is a physical property that causes matter to experience a force within an electromagnetic field.
In simple terms, the charge of an atom is the number of protons minus the number of electrons.
Electron Charge
Electrons are present with an electric charge of negative 1, and their mass is one by 1830 times the mass of neutrons and protons. The e is the symbol of electron charge. The electron charge is the fundamental physical constant, which represents the naturally occurring unit of electric charge which has a value of 1.602 X 10-19.
Like all elementary particles, electrons also exhibit properties of both particles and waves, which is that they can collide with other particles and can be diffracted like light.
According to the International System (SI) of Units, a unit of charge is called a coulomb and is denoted by the symbol C. A coulomb is the unit of the electric current.
The electron is negatively charged because the proton is positively charged. A proton attracts an electron by the fact that opposite charges attract each other while two electrons repel each other.
Energy Level
Atoms have energy bands and energy gaps. Each electron is found in any of these energy bands. The two energy bands are the conduction band and valence band. Between these bands (valence and conduction band), the gap is called the forbidden energy gap. This gap also helps determine the electrical property of the material that the gap increases. The gap decreases in the conductor, and the gap is intermediate in the semiconductor.
Atom
John Dalton, in 1808 proposed that the atom is the smallest indivisible particle of matter. Atomic radii are in order of 10−8 cm. It consists of three subatomic particles called electrons, protons and neutrons.
Protons
Rutherford discovered protons on the basis of an anode ray experiment. It carries a positive unit charge (+1.6 × 10-19 C). The mass of the proton is 1.007276 u.
Some of the characteristics of anode rays are:
- i) They travel in a straight line and possess mass many times heavier than the mass of an electron.
(ii) They do not originate from an anode, but they are produced in the space between the anode and the cathode.
(iii) They also cause mechanical motion, and electric and magnetic fields deflect them.
(iv) Specific charge (e/m) for these rays depends upon the nature of the gas taken and is maximum for H2.
Neutrons
Neutrons are neutral particles. Chadwick, in 1932 discovered that the mass of the neutron is 1.675 X 10-24 g or 1.008665 amu or u.
Some Other Subatomic Particles:
(a) Positron: It is a Positive electron ( +1 e), discovered by Dirac in 1930 and Anderson in 1932.
(b) Neutrino and antineutrino: These are particles of small mass and have no charge, as stated by Fermi in 1934.
(c) Meson: Yukawa discovered it in 1935 and Kemmer. These are unstable particles, and they include pi ions [ π–, π+ or π0 ].
(d) Anti-proton: It is a negative proton produced by Segre and Weigland in 1955.
Atomic Number (Z)
The atomic number of an element denotes the total number of protons present in the nucleus or the total number of electrons present in the neutral atom.
Mass Number (A)
The mass of the nucleus is because of protons and neutrons, so they are called nucleons. The total number of nucleons is called the mass number of the atom. (Mass number of an element = number of protons + number of neutrons)
Developments Leading to the Bohr’s Model of Atom
The two developments played a major role in Bohr’s model, and those are as follows:
(i) The Dual character of electromagnetic radiation states that radiation possesses wave and particle-like properties.
(ii) The Atomic spectra are defined by the electronic energy level in atoms.
Conclusion
There are three subatomic particles: electrons, neutrons and protons. Electrons are negatively charged subatomic particles present inside the atom. It carries a negative charge ( 1.6 X 10-19 C). Neutrons are neutral particles. Neutrons are neutral particles. Rutherford discovered protons on the basis of an anode ray experiment, It carries a positive unit charge (+1.6 × 10-19 C)
