Did you ever find yourself wondering – what are particles? This question is undoubtedly exciting yet confusing as its answer might twist your head and leave you confused. The beauty of the definition of particles lies within the wide variety of opinions on the topic.
A particle, in simpler terms, can be defined as a tiny bit of anything. There have been different opinions and discussions on its definition, yet all are interested in their particular ways. Whether it’s the chair in your house or the useless cardboard box you might have kept for no reason, everything is made up of particles.
Scientifically, particles are defined as a body having finite mass and internal structure but negligible dimensions. These tiny particles can also be classified as subatomic particles made of three constituents – electrons, protons, and neutrons – and they hardly take up any space.
Atoms: A Brief
The idea that everything is made up of atoms was first introduced by John Dalton. He published his theory in 1808, which was quick to gain the attention of all science enthusiasts. Dalton’s atomic theory was particular because it was the first of its kind to be supported by the law of conservation of mass and constant.
There are four parts of Dalton’s atomic theory, where he puts forward the following conclusions:
- All matter is made up of atoms divided into many subatomic particles.
- All atoms present in an element are identical in their mass and properties.
- Compounds are made up of two or more different types of atoms.
- A chemical reaction rearranges an atom.
Atoms generally contain space. The nucleus present in the centre of an atom is positively charged and mainly contains its mass. It is made up of protons, which are positively charged, and neutrons, which generally have no charge. These atoms are primarily surrounded by electrons, which are generally present in all atoms and are negatively charged.
Let us see how these three components of atoms were discovered.
Who Discovered Electrons?
Electrons are low-mass, negatively charged particles present in all the atoms. It acts as a primarily sole carrier of electricity in solids.
It was first discovered by J.J. Thomson, who carried the experiments in a discharge tube by taking the gas at low pressure of 0.01mm Hg. Thomson took two parallel aluminium plates and shot a beam of cathode rays between them.
He observed that the movement of the rays after being directed towards the end of the tube was highly dependent on the nature of the aluminium plate. According to his observation, the rays moved up when the upper aluminium plate was positive and vice versa.
He also observed that the deflection of cathode rays was proportional to the potential between the aluminium plates. After playing both kinds of deflections, Thomson concluded that the rays contained negatively charged components. He proceeded to name this component electron.
Although Thomson successfully marked finding the existence of electrons, he could not jot down the exact value that it held. The charge value electrons hold is calculated by Robert Millikan, a well-known American physicist.
Millikan’s famous work – the oil drop experiment – is credited for finding the value of electrons. He measured the electron’s charge to be 1.6*10-19 Coulombs, a value that is of extreme importance even today. His experiment revolved around dropping negatively charged oil droplets and inferring the observations.
To know more about the electrons, refer to the Important Concepts of Chemistry and NCERT Solutions and enhance your preparation levels.
Who Discovered Protons?
Protons are positively charged particles present in all the atoms and generally in the nucleus of a hydrogen atom. Ernest Rutherford first discovered them in 1911 through his most famous experiment called the gold foil experiment.
Rutherford worked with alpha particles to go about this experiment. He set up an alpha particle emitter in front of a zinc sulphide (ZnS) screen. This screen was fluorescent.
After that, he kept a fragile gold foil between the alpha particle emitter and the screen. Once the setup was ready, he projected the alpha particles on the gold files and observed their nature of deflection.
Based on the above experiment, Rutherford was able to draw the following operations:
- The majority of the alpha particles emitted could pass straight through the gold foil. They banged straight in front of the zinc sulphide fluorescent screen.
- However, not all alpha particles travelled in a straight line. A significant few amongst the straight travelling alpha particles ended up on a slightly deviated path. They went through a fraction of deflection, and hence the hits on the screen were slightly to the side of the straight deflection hits.
- There were very few alpha particles that we could completely bounce back. One about 20,000 alpha particles were able to retrace their path back after a deflection from the gold foil.
Through the above observations, the following conclusions were drawn:
- The majority of an atom’s mass is concentrated in its nucleus. It contains positively charged ions and is a small core located in the centre of the atom.
- There were negatively charged ions, called electrons, revolving around the nucleus. Since they numerically combine to be equal to the combined charge of protons, the charge of an atom is neutral.
Who Discovered Neutrons?
Neutrons carry no charge present in all the atoms and have the same mass as protons. Sir James Chadwick first discovered neutrons in the year 1932. He was also awarded in the year1935 with the Nobel Prize in physics for the same discovery.
James Chadwick did his experiment on a beryllium sheet, which led to the production of uncharged radiation. This radiation was observed with the help of an ionisation chamber. Thus, he concluded that uncharged particles have the same mass as a proton.
Before Chadwick’s discovery, scientists confused neutrons with photons. However, Chadwick used the Joliot curie experiment and changed the bombarding target – using targets other than paraffin. He continued to analyse and infer what happened after he bombarded these particles on different targets – and finally concluded that this uncharged component of the atom was, in fact, not a photon but something else.
Chadwick fired neutrons at the targets, which were rich in protons. The results of this experiment included neutrons smashing protons and knocking them out. He calculated the mass of this new particle, now known as a neutron – and discovered that its mass was slightly more than a proton.
Conclusion
Hence, to sum up, we have covered the discoveries of the three components of atoms:
- JJ discovered electrons. Thomson in the year1897.
- Rutherford discovered protons in the year 1911.
- Chadwick discovered neutrons in 1935.
The discoveries of these particles are fundamental even today. The values and experimental observations gifted to us by these well-known and genius scientists have helped us solve numerous problems in our daily life.
These discoveries have also paved the way for several other discoveries and refinement of theories – carried out by scientists these men deeply inspired.
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