Subatomic Particles

An atom consists of several small particles(or subatomic particles). Three important subatomic particles are Electron, Proton, and Neutron. Subatomic particles are main constituents of the atom we call as fundamental particles. The nucleus is the center of an atom.The constituents of the nucleus, both proton, and neutron, are often referred as nucleons.

  Read Must: Structure of Atom.

Subatomic Particles Definition

The unit (regarded as single and complete) of energy and matter is the subatomic particle. Its composition or constitution of something called as matter. Modern atomic theory says that an atom has fundamental particles: electron, proton, and neutron.

Subatomic Particles of an Atom

Electrons always revolve around the nucleus at a very high speed.They are the subatomic particles but they are not a part of nucleons. It has a negative charged and having a very small mass of 1/1840 of the hydrogen atom.Electron decides the chemical and physical properties of an atom.

Protons carry a charge opposite to the electron. It is a subatomic particle found in the nucleus of every atom. The mass of a proton is slightly less than the mass of the neutron. The atomic number is equal to the number of protons.

The hydrogen is the only atom that does not include the neutron.

Subatomic Particles

 Subatomic Particles List

According to new discoveries, only a few new subatomic particles list as follow:

B meson Antineutrino
Positron Antiproton
Muon Photon
Gluon Alpha particle
down-antiquarks charm antiquark
There are much more we have listed only a few.

3 Subatomic Particles

Name Symbol Located at
Electron e  or -1eo or e Around Nucleus
Proton P or 1p1 In the Nucleus
Neutrons n or 0n1 In the Nucleus

Mass of Subatomic Particles

Name Mass (In kg) Mass in amu Relative Mass
Electron 9.109534 × 10-31 5.4858026 × 10-4 1/1837
Proton 1.6726485 × 10-27 1.007276471 1
Neutrons 1.6749543 × 10-27 1.008665012 1

Charges of Subatomic Particles

Name Actual (in Coloumb(C)) Relative Charge
Electron 1.6021892 × 10-19 -1
Proton 1.6021892 × 10-19 +1
Neutron 0 0

Discovery of Subatomic Particles

Element Discovery by Scientist
Electron JJ. Thomson
Proton Goldstien
Neutron Chandwick
Nucleus Ernest Rutherford

Let’s have the discussion about the discovery of fundamental particles of atom i.e Protons neutrons and electrons.

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 conduction of electricity through gases taken in a discharge tube.

Protons Neutrons And Electrons

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.

Protons Neutrons And Electrons

 

Anode Rays Cathode Rays
H→ H+ e
O → O+ e

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

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.

Properties of Subatomic Particles

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.Protons Neutrons And Electrons

(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.

Protons Neutrons And Electrons

(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 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.

  1. Neutrons which are not a part of the nucleus we call as a free neutron.
  2. Free neutrons are very much unstable. Free neutrons helpful in the nuclear power production. Protons and neutrons are together as nucleons.
  3. The number of neutrons determines the isotope along with their physical properties.
  4. In general, greater the mass means the higher number of neutrons, higher melting point, and boiling point.
  5. Is there any metal that does not include protons: Yes, under special circumstances stars and powerful particle accelerators have no proton

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