An atom consists of several small particles (or subatomic particles). Numerous times multiple questions arise about Proton Neutron Electron, who discovered these subatomic particles and how discovery took place. Let’s answer these questions one by one.
Proton Neutron Electron
An atom is the smallest particle of matter that has the independent existence. An Atom is too small to be viewed even under a powerful microscope. As we told earlier that an atom consists of several small particles. We have listed below-
|Element||Discovered by Scientist|
We can visualize an atom as a sphere. An atom has two major divisions –
- In the centre of the atom, there is a nucleus the size of the nucleus is extremely small compared to the size of the atom.
- Observe that the nucleus consists of two types of particles known as protons(+ve charge) and neutrons (no charge).
- The electrons revolve around the nucleus in fixed orbits these are the electron shells.
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An atom consists of three elementary particles namely proton neutron and electron. Atoms of different elements are built up from different numbers of these fundamental particles.
- If an atom has one proton and one electron it forms an atom of hydrogen.
- But if the number of protons Neutrons and electrons are eight each. Then we have an atom of oxygen.
So far we have discussed the Location and scientist name who discovered the Proton Neutron Electron. Let’s go for the properties of Proton Neutron Electron.
Properties of Proton Neutron Electron
The properties of subatomic particles are listed below:
Properties of Electrons
Some important properties of an electron as follows:
- (i) They cast shadows of solid objects placed in their path. Hence they travel in straight lines.
- (ii) When allowed to fall on light paddle wheels, the rays cause its rotation. Hence they must consist of material particles.
- (iii) The rays possess heating effect.
- (iv) The rays cause ionization of gases through which they pass.
- (v) They produce X-rays when they strike against hard metals like tungsten.
- (vi) They penetrate through matter.
- (vii) They produce fluorescence on certain substances such as zinc sulphide.
- (viii) They affect the photographic plates.
- (ix) Cathode rays get deflected in a magnetic field in a direction as to indicate that they are negatively charged.
- (x) When subjected to electric fields, the rays deviate from their straight path towards the positively charged plate. Hence the rays must be made up of negatively charged particles. These particles were named electrons.
Properties of Protons
The properties of these protons or canal rays were studied and are as follows:
- (i) These rays are deflected by electric and magnetic field just as cathode rays but in the opposite direction showing that unlike cathode rays they consist of positively charged particles and therefore, called them as positive rays.
- (ii) The ratio of Charge/mass(e/m) of these particles is found vary and depends upon the nature of the gas contained in the discharge tubes.
- (iii) The mass of these positively charged particles is about 1837 times more that of an electron or is almost the same as that of atoms of hydrogen gas in the discharge tube.
- (iv) The e/m ratio is always less than that for cathode rays.
- The lightest positively charged particle discovered was for hydrogen gas. Its mass is approx. same as that of a hydrogen atom and its charge exactly equal in magnitude but opposite in sign to the negative charge on an electron. This positively charged particle was called proton.
Properties of Neutron
- (i) They are having no charge and present inside the nucleus of an atom.
- (ii) Neutrons are present in all atoms of the different element except the hydrogen have only one proton.
- (iii) The Number of neutrons decides the melting and boiling point.
- (iv) The existence was predicted by the scientist Rutherford.
- (v)It is 1839 times heavier than the mass of an electron.
Protons and Neutrons
There are few more important points of protons neutrons. let’s discuss one by one.
- Neutrons which are not a part of the nucleus we call as a free neutron.
- Free neutrons are very much unstable. Free neutrons helpful in the nuclear power production. Protons and neutrons are together as nucleons.
- The number of neutrons determines the isotope along with their physical properties.
- In general, greater the mass means the higher number of neutrons, higher melting point, and boiling point.
- Is there any metal that does not include protons: Yes, under special circumstances stars and powerful particle accelerators have no proton
Discovery of Proton Neutron Electron
Let’s have the discussion who and how the fundamental particles of atom i.e Proton neutron electron were discovered.
Discovery of Electron
Modern views about the structure of atom are based upon the discovery of a negatively charged particle termed as electron by Sir J.J. Thomson in 1987. The electrons were discovered during the study of the conduction of electricity through gases taken in a discharge tube.
It consists of a glass tube with two metal electrodes sealed in either end. A high voltage about (10,000 volts) is passed through the gas contained in the discharge tube at very Cathode low pressure. The air in the discharge tube is removed by a vacuum pump.
It was observed that at very low pressure (about 10-3 atm) a greenish light was emitted by the glass tube itself. The emission of greenish from the glass tube was caused by invisible rays emanating from the cathode. These rays which originated from the cathode were given the name “Cathode Rays”.
Discovery of Protons
As electrons are present in all atoms and atom, as a whole, is electrically neutral, it is essential that an equal amount of positively charged particles be present in an atom.
In 1886, Goldstein discovered these positive rays in the discharge tube using a perforated cathode. Such rays passed through the holes in the cathode and their properties could be studied. These rays were called Anode rays or canal rays or positive rays.
|Anode Rays||Cathode Rays|
Origin of positive rays
These positively charged particles are formed from the neutral atoms of the gas in the discharge tube due to knocking out of one or more electrons by the fast-moving electrons from the cathode. The positive particles from other gases are supposed to be made up of two or more units of protons.
Discovery of Neutrons
In 1913 Mosley experimentally proved that the nuclear charge of an atom is numerically equal to the atomic number Since an atom is electrically neutral, the nuclear charge (or no. of protons) must be equal to the number of planetary electrons. Therefore, an atomic number generally denoted by the letter Z is also equal to the number of planetary electrons.
This atomic number (Z) = nuclear charge or number of protons in the nucleus number of planetary electrons in a neutral atom.
To understand the discovery of the neutrons, take the case of hydrogen and helium atoms. Hydrogen, being the first element, has atomic number 1. Thus, it contains one proton and one electron. Helium, the second element in the periodic table has an atomic number 2. Therefore, its atom should have double mass than that of a hydrogen atom.
But in reality, its mass is found to be four times than that of the hydrogen atom. It was found that all other elements except hydrogen show similar weight discrepancies(illogically) and were at least twice as heavy as the number of their protons.
To account for these discrepancies, Rutherford (1920) had suggested that in addition to the two oppositely charged particle in an atom there was a possibility of the presence of a particle of essentially the same mass as that of a proton but without any charge.
This animation video helps you more Discovery of neutrons
Chadwick (1932) established the existence of such neutral particles called Neutrons by bombardment of the nucleus of lighter elements like Be or B with high-speed particles.
94Be + 42 He –→ 12 6C + neutron
After the discovery of neutrons, many other particles such as positrons mesons, antiprotons etc. were also discovered.
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