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Subatomic Particles

The basic unit of matter which consists of a dense central nucleus surrounded by a cloud of negatively charged electrons is called as atom. In any atom , the center part that is known as nucleus consist of two subatomic particles ; positively charged protons and electrically neutral neutrons, while negatively charged electrons are bound to the nucleus by the electromagnetic force.

Except noble gases; atom cannot exist in free state and they bound to each other to form a molecule. An atom is always electrically neutral due to presence of equal number of protons and electrons. If the number of electron and proton is not equal, atom gets some charge and known as ion.

The particles present in an atom are termed as subatomic particles. There are mainly three subatomic particles i.e., Electrons, protons and neutrons. The number of protons in any atom is called as atomic number which determines the chemical element.

The number of neutrons in an atom is used to identify the isotope of the element. Electrons present in any atom involve in chemical reaction and responsible for the physical and chemical properties of elements.

 

What is a Subatomic Particle?

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Each atom consist a certain number of particles called as subatomic particles. Subatomic particles can be classified in two types.
  1. Elementary particles
  2. Composite particles

Subatomic Particles of an Atom

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Elementary particles

These are fundamental particles which are not composed of any other particles. They can be classified on the basis of spin of particles.

  1. Fermions: These particles have half-integer (1/2) spin. All fermions have their own antiparticles and hence also known as Dirac fermions. Fermions are the basic building blocks of all matter. Total twelve types of elementary fermions: six quarks and six leptons.
  2. Quarks: They are constituent particles of hadrons in which they interact through the strong interaction. These particles carry fractional charge but they combine in the group of three or two so only integer charge is observed in nature. Total six flavors of quarks are possible; three positively charged quarks known as up-type quarks and the three negatively charged quarks called as down-type quarks.
  3. Leptons: These particles do not interact through strong interaction like quarks. Electron is an example of lepton. Each lepton has one anti particle like the antiparticle of the electron is the anti-electron also called as positron. Just like quarks; there are total six leptons; the three charged leptons are called electron-like leptons; however the neutral leptons are called neutrinos.
  4. Boson: these particles have integer spin. Different type of bosons and their antiparticles are as follows.

Name
Symbol
Antiparticle
Charge (e) spin
Photon ν Self 0, 1
W boson
W W+
-1, 1
Z boson
Z
Self
0, 1
Gluon g
Self
0, 1
Higgs boson
Ho
Self
0, 0
Gravitation
G Self
0, 2


Composite particles


These particles made due to the combination of one or more elementary subatomic particles like protons are made from the combination of two up quarks and one down quark.

Composite particles are three types.
  1. Hadrons: They are made of quarks which are held together by the strong force. Hadrons are categorized in two types; Baryons and Mesons.
  2. Baryons: These composite particles made up from the combination of fermions like protons and neutrons.
  3. Mesons: These composite particles are formed from the combination of elementary particles; bosons. For example; pions and kaons.

Subatomic Particles List

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Particle
Symbol
Charge
Electron e- Negative
Proton
p
Positive
Neutron
n
Neutral
Positron
e+
Positive
Neutrino
u
Neutral
Antiproton
p-
Negative
Gravitation
G
Neutral
Photon
? Neutral
V particle
V
±
Kappa meson
k meson
±
Pai meson
π meson
±
Zeta meson
ξ meson
±
Tatu meson
T meson
±

Out of all subatomic particles the most important particles are electron, proton and neutron. In an atom, neutron and proton located in nucleus and electrons revolve around the nucleus in a certain orbits.

Electrons

  1. Electrons discovered by William crooks and J.J. Thomson during the study of cathode rays in a gas discharge tube also known as crooks tube.
  2. Electrons are fundamental particles of an atom with negative charge named by J.S. Stony.
  3. They have unit negative charge and the charge by mass ratio of electron is 1.76 x 108 coulomb/gm.
  4. The value of negative associated with electron is measured by R.A. Millikan through an oil drop experiment and estimated as 1.602 x 10-9 coulomb or 4.803 x 10-10 e.s.u.
  5. The mass of electron is 9.1091 x 10-28gm or 0.0005486 a.m.u.
  6. Electron is 1837 times lighter than one hydrogen atom. The gram molar mass of electron is 5.483 x 10-4.
  7. There are 1.1 x 1027 electrons in one gram of that.
  8. The mass of 1 mole electrons is 0.5483 mg.
  9. One mole of electrons carries one Faraday (96500 coulomb) charge.
  10. Electrons of any atom involve in chemical reaction of an element, hence the number and position of electrons in atom is responsible for their chemical and physical properties of elements.

Protons

  1. Protons are discovered during the study of canal rays by Eugene Goldstein in 1886. Canal rays also termed as positive rays also as they attracted towards negative electrodes.
  2. Canal rays travel in a straight line and effect photographic plates.
  3. Due to positive charge, positive rays are affected by electrical and magnetic field which proves that they have some charge.
  4. Canal rays formed from positive charged particles known as protons.
  5. Just like electrons; Protons are also fundamental particle of an atom with positive charge discovered by Goldstein and named by Thomson and Wine.
  6. The mass of proton is equals to the mass of one hydrogen atom or 1837 times heavier than the mass of electrons.
  7. The magnitude of charge by mass ratio (e/m) also known as specific charge, for proton is 9.578 x 104 coulomb /gm.
  8. The charge (e) on proton considered as 1.6 x 10-19 and mass as 1.6725 x 10-24 gm.
  9. In a neutral atom, the number of protons is equals to the number of electrons and also termed as atomic number.
  10. The chemical and physical properties of an element are periodic function of their atomic number.
  11. Protons and neutrons are termed as nucleons and responsible for the mass of atom.
  12. The total sum of number of protons and neutrons is known as mass number of atom.
  13. The charge on protons is 1.602 x 10-19 coulomb or 4.8 x 10-10 e.s.u while mass is 1.6725 x 10-24gm or 1.6725 x 10-27 kg or 1.6725 x 10-29 quintal.
  14. Each proton is 1837 times heavier than electron and the mass of one hydrogen atom is equals to the mass of proton that is 1.00757 a.m.u. The gram molar mass of proton is 1.6725 x 10-24 x 6.023 x1023 (Na) =1.008.

Neutrons

  1. Neutrons are neutral subatomic particles located in nucleus with positively charged protons.
  2. In 1932, Chadwick discovered these neutral particles by the bombardment of alpha particles on Beryllium.
  3. He observed the emission of a radiation which have high penetration power but electrically neutral as they were unaffected by magnetic and electric fields.
  4. He found that the mass of these particles approximately same as for the mass of protons and named as neutrons.
  5. 4Be9 +2He4 6C12 +0n1
  6. Neutrons are subatomic particles present in nucleus with protons.
  7. They are electrically neutral particles with almost same
  8. mass as for protons that is 1.6748 x 10-24gm or 1.00893 a.m.u.
  9. The gram molar mass of protons is 1.00893 with 1 x 1012 Kg/cc density.
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Mass of Subatomic Particles

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Particle Symbol Mass(a.m.u)
Mass with respect to electron mass = 9.11 x 10-28gm
Electron
e-, β- 0.0005486 1
Proton
p 1.00758
1.836
Positron
e+, β+ 0.0005486
1
Neutrino
u <0.000022
<0.04
Antiproton
p-
0
1.836
Gravitation
G
0
0
Photon
? 1.000893
0
Neutron
n
0.1152
1.8385
Negative μ meson μ-
0.1152
210
Positive μ meson
μ+ 0.1514
265
Negative π meson π-
0.1514
276
Positive π meson π+ 0.1454
276
Neutral π meson π 0.7680
265
Positive X meson
X+ 0.7680
1400
Negative X meson
X- 0.3018
1400
ξ meson
ξ 0.5349
550
T meson
T 0.6035
975
K meson
K
1.2069
1100
Negative V meson
V-
1.2069
2200
Positive V meson
V+ 1.2069
2200
Neutral V meson
V 0.41643
850
More topics in Subatomic Particles
Properties of Subatomic Particles
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