Electrons are subatomic particles that, along with protons and neutrons, come to form the most fundamental part of atoms. For a long time, the atom was considered to be the final structure of an element. The term ‘atom’ being wholly representative of that thought since it comes from the Greek word meaning indivisible. However, all that changed when in 1897, the English physicist J.J. Thomson through his now-famous cathode ray tube experiments, led to the discovery of electrons as being a part of subatomic particles, i.e., particles which make up the atom.
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An electron is defined as a subatomic particle that is negatively charged and can exist either in a free state, i.e., not bound to any atom or attached to the nucleus of an atom. In atoms, the electrons are represented as existing in spherical shells of heterogeneous radii based on the energy levels of the electron. Thus the energy contained in the electron is directly proportional to the size of the spherical shell that the electron exhibits. Electrons are usually denoted by the sign e-. Now that you are familiar with the electron definition in chemistry let us understand the properties of an electron.
Subatomic particles come with their own set of specific properties that are unique to them. Thus the properties of protons, neutrons, and electrons are, for the most part, well defined. Here are some of the properties of an electron:
Mass of an electron: The mass of an electron is 9.1 x 10-31 kg or 0.000548579909 atomic mass units. The mass of an electron can also be represented as being 1/1840 of the mass of a hydrogen atom. Now, since the mass of hydrogen atom is 1 u, the relative mass of an electron can also be represented as 1/1840 u
The absolute mass of an electron: Absolute mass of an electron is 9 x 10-28 grams
Charge of an electron: The electron is a negatively charged particle, and therefore the effective charge is -1.
Electrical charge: Since the charge of electrons is -1; the electrical charge should be 1.602 x 10-19 coulombs.
Electrons revolve around the nucleus of the atom of the element in specific, well-defined orbits.
The properties of an electron are unaffected and independent of the gas present in the discharge tube.
Electrons also exhibit a two-sided nature defined as wave-particle duality, which means that the electron, which is a particle under specific circumstances, behaves as a wave.
Electrons were discovered in 1897. However, the electron meaning and its significance came to be redefined with the discovery of the proton in the period between 1911 - 1919 and the neutron in 1932. With the discovery of the other two subatomic particles, the entire model of atomic structure, as we know it today, was established.
Protons are defined as the positively charged subatomic particles in the nucleus of an atom. They are 99.86% as large as protons, and the number of protons present in an atom is unique for each element. For instance, hydrogen has one proton, oxygen has eight, and carbon has six.
Neutrons were already theorized by the scientist Rutherford when he discovered the proton but neutrons were discovered by Chadwick in 1932. Neutrons were subatomic particles with no charge or neutral charge, hence the name ‘neutron’. Except for the hydrogen atom, neutrons make up the constitution of all other elements of the periodic table. The neutron's mass is larger than a proton but only slightly.
The discovery of electrons in chemistry was substantiated by an electric discharge in cathode-ray tubes. Thomson noted that the rays inside the tube were deflected, which was inferred as the presence of a negatively charged particle inside the vacuum tube that made such a phenomenon possible. His electron definition in chemistry came to be represented as the plum-pudding model based on the fact that there were a large number of electrons present in a form that produced an overall positive charge hence establishing an overall neutral charge. With the discovery of protons and neutrons, this model was replaced by the modern atomic model that we see today.
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1. Who and When Discovered the Electron?
The electron was discovered by the British physicist J.J.Thomson while conducting experiments with the cathode ray. It was discovered in 1897.
2. How was the Electron Discovered?
JJ Thomson’s experiment on cathode tubes eventually led to the discovery of the electron. Cathode ray tubes are essentially sealed vacuum chambers made up of glass. When a high voltage is applied across the electrodes placed on the ends of the tube, a beam flows from the negatively charged pole to the positively charged pole. To determine the existence of electrons, Thomson put up two oppositely charged electric places around the cathode ray. The cathode ray was observed by Thomson to be deflected towards the negatively charged electric plate. Thereby effectively proving that the cathode ray consisted of negatively charged particles.
3. Atoms are Electrically Neutral - Explain
Let us first understand what the term ‘electrically neutral’ means. When an atom is considered to be electrically neutral, it means that the overall charge that the atom has is zero. An atom consists of protons, neutrons, and electrons. As protons are positively charged, electrons are negatively charged, and neutrons are neutrally charged. Now, if an atom has the same number of protons and electrons, then the atom is considered to be electrically neutral.