Fundamental Particles

Fundamental Particles: Many complex chemical phenomena occur around us, and these are explained on the basis of the matter which is made up of molecules. Molecules, in turn, are made up of atoms. Dalton’s Atomic Theory proposed that an atom is an indivisible particle. But research findings of the last hundred years on the study of gases in particular and then of solids led to discovering the fundamental particles, i.e., electron, proton, and neutron. Understanding this topic thoroughly will help you in science subject. It will give insight on the important topics of Physics.

Various atomic models to indicate the arrangement of these fundamental particles in an atom were proposed. An atom consists of a nucleus in its centre. Protons and neutrons are present in the nucleus, while electrons lie outside the nucleus. In this article, we will learn about the Fundamental Particles of an atom. Read full article to get complete details.

Fundamental Particles Introduction

Our modern ideas of the structure of matter began to shape in the early nineteenth century with Dalton’s atomic theory. The theory states that 

1. All matter is composed of tiny indivisible particles called atoms. The atoms are the building blocks of elements.
2. All atoms of the given element are identical in size, mass, and characteristics.
3. The atoms of elements differ from each other.
4. The compounds contain atoms of different elements combined in a whole-number ratio.
5. Atoms can neither be created nor be destroyed in chemical reactions.

Dalton’s vision of atoms as indivisible particles is now known to be incorrect. A large number of experiments conducted by Thomson, Rutherford, and Moseley, Chadwick, and others revealed that the atom has a complex structure.

Dalton’s atomic theory explains the law of conservation of mass, law of constant proportions, and law of multiple proportions successfully. Still, it cannot explain why glass or ebonite generates electricity when rubbed with silk or fur. 

All atoms except the hydrogen (protium) atom are composed of three fundamental subatomic particles electrons, protons and neutrons. These three are regarded as fundamental particles because they are the main constituents of an atom.

It is now known that more subatomic particles such as positron, neutrino, antiproton, pions, and mesons have been discovered. Many of them are unstable and exist for a fraction of a second only.

What are Fundamental Particles?

The fundamental particles of an atom are necessary to understand the chemical interactions. Protons are positively charged particles present in the atom’s nucleus, while electrons are negatively charged particles present in the extranuclear part of the atom. Neutrons are the neutral particles present in the nucleus along with the protons.

Discovery of Electron

Based on experiments on electrical discharge through gases, the structure of an atom can be known.

An electron is a subatomic particle that carries a unit negative charge. Thomson discovered it during the study of cathode rays in a discharge tube experiment. Sir William Crookes had designed this discharge tube.

A cathode ray discharge tube is a glass tube fitted with two metallic electrodes, which have been sealed. The tube is connected to a side tube through which it can be evacuated to any desired pressure with the help of a vacuum pump. The discharge tube is filled with the gas under study.

The cathode rays are produced when gas at low pressure is subjected to high electric discharge.

Characteristics of Cathode Rays

1. The cathode rays start from (\( – {\text{ve}}\) electrode) and move towards the anode (\( + {\text{ve}}\) electrode). So they have been named as they were believed to be coming from the cathode. Electrons are removed from an atom that will move from cathode to anode as they negatively charge.
2. The cathode rays are invisible, but their behaviour can be observed with the help of fluorescent materials such as zinc sulphide so that strong fluorescence is produced when electrons bombard the surface. Cathode rays also can have phosphorescence—for example, television picture tubes.
3. The cathode rays travel in a straight line in the absence of an electric or magnetic field.
4. The cathode rays are deflected towards the positively charged plate in the electric field and south pole in the magnetic field. It shows that the cathode rays consist of a stream of negatively charged particles called electrons. 
5. Cathode rays produced are independent of the nature of the cathode material and the nature of the gas present in the cathode ray tube. Hence, electrons were considered as constituent particles of all atoms.

Charge to Mass Ratio of Electron

 J.J. Thomson determined the ratio of the electric discharge to the mass of the electron using a cathode ray discharge tube.

Thomson applied electric and magnetic fields perpendicular to each other and the path of the electrons.

The extent of deviation of the particles from their path in the presence of electrical and magnetic fields depends upon:

1. The magnitude of the negative charge on the particle: The greater the magnitude of the charge on the particle, the greater is the interaction with the electric or magnetic field, and thus greater is the deflection.
2. The lighter the mass of the particle, the greater is the deflection. 
3. The deflection of electrons from its original path increases with the increase in the voltage across the electrodes or the strength of the magnetic field.

When the magnetic field alone is applied, electrons strike the cathode ray tube at point \({\text{C}}\). Similarly, when the electric field alone is applied, the electron strikes at point \({\text{A}}\). Finally, when both the magnetic and electric fields are off or balanced to cancel each other’s effects, the electron strikes at point \({\text{B}}\).

Thomson determined the value of charge to mass ratio as

\(\frac{{\text{e}}}{{{{\text{m}}_{\text{e}}}}} = 1.758820 \times {10^{11}}{\text{Ck}}{{\text{g}}^{ – 1}}\)

Where \({{\text{m}}_{\text{e}}}\) is the mass of electron in \(\mathrm{kg}\), and \(\mathrm{e}\) is the magnitude of the charge on the electron in coulomb \({\text{‘C’}}\).

Charge on the Electron

R.A. Millikan determined the charge on the electron by his famous experiment “oil drop method”. Millikan found that the charge on the oil drops was always an integral multiple of \(1.6 \times 10^{-19}\) coulombs, indicating the electron’s charge to be \(-1.6 \times 10^{-19} \mathrm{C}\). The presently accepted value of the electric charge is \(-1.6022 \times 10^{-19} \mathrm{C}\).

Knowing the values of \(\frac{{\text{e}}}{{{{\text{m}}_{\text{e}}}}}\) and charge of an electron, it is possible to calculate the mass of an electron.

\({{\text{m}}_{\text{e}}} = \frac{{\text{e}}}{{\frac{{\text{e}}}{{{{\text{m}}_{\text{e}}}}}}} = \frac{{1.6022 \times {{10}^{ – 19}}{\text{C}}}}{{1.758820 \times {{10}^{11}}{\text{C}}\,{\text{k}}{{\text{g}}^{ – 1}}}} = 9.1094 \times {10^{ – 31}}~{\text{kg}}\)

This mass is termed as the rest mass of an electron. It has been found that the mass of an electron is approximately the mass of a hydrogen atom. The mass of electrons in relative units is \(0.0005486\) amu.

Discovery of Proton

A Proton is a subatomic particle that carries a positive unit charge. Rutherford suggested the name proton. 

The positive rays or canal rays were discovered by Goldstein using a perforated cathode in the discharge tube. The characteristics of positively charged particles are:

1. The positive rays or anode rays travel in the opposite direction to the cathode rays.
2. The deflection of anode rays in an electric and magnetic field is opposite to that of cathode rays.
3. The anode rays are attracted towards the negative plate in the electric field and towards the north pole in a magnetic field. It means that these rays consist of positively charged particles.
4. Unlike cathode rays, the charge to mass ratio of positive rays depends upon the nature of the gas taken in the tube.
5. The e/m of positive rays is considerably smaller than that of cathode rays. Thomson determined the e/m value of positive rays. It varies with the nature of the gas. It is maximum when the lightest gas hydrogen is taken in the discharge tube. The value is \(9.58 \times {10^7}{\text{C}}\,{\text{k}}{{\text{g}}^{ – 1}}\). 

For example, when the gas in the discharge tube is hydrogen, the mass of a positive particle is almost identical to that of the hydrogen atom. If the gas in the tube is oxygen, the positive particle has a mass almost similar to that of the oxygen atom.

The lightest positive ions are produced when the gas in the tube is hydrogen. A proton has a positive unit charge. So, the unit of positive charge is that associated with \({{\text{H}}^{\text{ + }}}\) i.e., a proton has a charge of \( + 1.6022 \times {10^{ – 19}}{\text{C}}\). The electric charge on the proton has the same magnitude as that of an electron but with a positive sign.

Proton is formed when nitrogen \(14\) is bombarded with alpha particles. It is the first transmutation carried out by Rutherford.

The mass of the proton in relative units is \(1.00727\) amu. Thus, the mass of a proton is \(1836\) times the mass of the electron and is nearly equal to the mass of a hydrogen atom.

Discovery of Neutron

A neutron is a Subatomic particle that carries no charge. Since neutrons have no charge, it is not easy to detect and characterise them. James Chadwick discovered neutron by bombarding lighter elements with alpha particles.

Neutrons are formed when beryllium \(9\) is bombarded with alpha particles.

\({}_4^9{\rm{Be}} + {}_2^4{\rm{He}} \to {}_6^{12}{\rm{C}} + {}_0^1{\rm{n}}\)

The mass of a neutron is \(1.67493 \times 10^{-27} \mathrm{~kg}\) or \(1.00867\) amu. It is 1838 times the mass of the electron and is slightly heavier than a proton. The properties of fundamental particles are listed below:

Fundamental Particles of Nucleus

The fundamental particles present in the nucleus of an atom are neutrons and protons. Protons and neutrons make up the tiny nucleus of an atom, while electrons exist outside the atomic nucleus in discrete energy levels within an electron “cloud.”

Fundamental Particles of Universe

Fundamental particles are the smallest building blocks of the universe. The critical characteristic of fundamental particles is that they have no internal structure. In other words, they are not made up of anything else. There are two types of fundamental particles:

1. Particles that make up all matter, called fermions
2. Particles that carry force called bosons

Summary

In this article, we learnt that an atom is a divisible particle and can be divided into electrons, protons, and neutrons. It includes the discovery and characteristics of electrons, neutrons, and protons. We looked into fundamental particles of matter, nucleus, and the universe.

FAQs on Fundamental Particles

The frequently asked questions on fundamental particles are given below:

Q.1. Which are fundamental particles?
Ans: An atom consists of three fundamental particles called protons, neutrons, and electrons. 

Q.2. What are the 12 fundamental particles?
Ans: The 12 elementary particles of matter are six quarks (up, charm, top, Down, Strange, Bottom), 3 electrons (electron, muon, tau) and three neutrinos (e, muon, tau).

Q.3. What are the fundamental particles that make up a proton?
Ans: Three quarks make up each proton, two “up” quarks (each with a two-thirds positive charge) and one “down” quark (with a one-third negative charge), and they are held together by other subatomic particles called massless gluons.

Q.4. What is a proton definition?
Ans: Proton, stable subatomic particle with a positive charge equal in magnitude to a unit of electron charge and a rest mass of \(1.67262 \times {10^{ – 27}}~{\text{kg}},\,1,\,836\) times the mass of an electron. 

Q.5. Which term is defined as the fundamental particles of protons and neutrons?
Ans: Quarks are the fundamental particles of protons and neutrons.

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