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Atomic And Nuclear Physics-Competitive Physics

Atomic and Nuclear Physics-Competitive Physics

             Physics topic – “Atomic and Nuclear Physics”, is important for all competitive exams like CET- Common eligibility Test,  SSC CGL, SSC CHSL, RRB NTPC,UPSC and other state civil services exams. In these exams, almost 4-5 Questions are coming from Physics. Let’s start the topic – Atomic and Nuclear Physics.

Atomic and Nuclear Physics for Competitive Exams

The Atomic Physics deals with the atom as a system consisting of a nucleus and electrons. This includes ions as well as neutral atoms. Atomic physics also help to understand the physics of molecules.

The Nuclear Physics deals with the nucleus as a system consisting of a nucleons (protons and neutrons). The most commonly known applications of nuclear physics are nuclear power generation. The nuclear physics has provided application in many fields, including:-

  • Nuclear medicine (Positron Emission Tomography, isotopes production, etc.)
  • Magnetic resonance imaging,
  • Ion implantation in materials engineering 
  • Radiocarbon dating in geology and archaeology.

Main difference in atomic and nuclear physics is in the scale. The term atomic deals with 1 Å = 10­-¹ºm, where Å is an angstrom, the term nuclear deals with 1 femtometer = 1 fermi =10-15 m.  

Atom:- The atom is the basic building block for all matter in the universe. An atom is composed of two regions: The nucleus, which is in the centre of the atom and contains protons and neutrons, and the outer region of the atom, which holds its electrons in orbit around the nucleus. atomic structure sukrajclasses.com

  • In an atom the number of protons and electrons are equal. Thus an atom is electrically neutral in nature.
  • The volume of an atom is about 15 orders of magnitude larger than the volume of a nucleus.
  • Examples of atom: Neon (Ne), Hydrogen (H), Argon (Ar), Iron (Fe), Calcium (Ca) etc.

Protons: – Protons are the positively charged particles which are present in the nucleus of an atom.

  • Protons were discovered by “Ernest Rutherford” in the year 1919, when he performed his gold foil experiment.
  • Example of proton: – silicon has 14 protons and 14 neutrons. Its atomic number is 14 and its atomic mass is 28.

Electrons: – The electrons are Negative charges particles and are not held very tightly in the atom so it is easy for them to move around.

  • Electrons are located in an electron cloud, which is the area surrounding the nucleus of the atom.
  • Electrons were discovered by “Sir John Joseph Thomson” in 1897.
  • Example of electrons: – hydrogen atom has atomic number 1. So, it has just one electron and one proton.

Neutrons: – Neutrons are located in the nucleus with the protons.  Neutrons have no charge, they are electrically neutral. The number of neutrons affects the mass and the radioactivity of atom.

  • This is represented by the symbol “N”.
  • Neutrons were discovered by “James Chadwick” in 1932.

Nucleons: – The nucleus contains protons and neutrons which are collectively called nucleons.

Atomic Mass Number: The mass number is defined as the total number of protons and neutrons in an atom.

  • It is represented by the letter ‘A.’
  • It is equal to “Z + N = A”
  • Example of atomic mass number: – Silicon has 14 protons and 14 neutrons. So, its atomic mass is 28.

Photon: – A photon is the smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light.

  • Photons are always in motion and in a vacuum, they travel at a constant speed (2.998 × 108 m/s). It is commonly referred to as the speed of light, denoted by the letter c. 
  • They have zero mass and rest energy. They only exist as moving particles.
  • They are elementary particles despite lacking rest mass.
  • They have no electric charge.
  • They are stable.

Atomic Number: The nucleus is composed of protons and neutrons. Total number of protons in the nucleus is called the atomic number of the atom.

  • It is represented by the symbol Z.
  • Atoms of different elements have different atomic numbers.
  • Example of atomic number: – Hydrogen has an atomic number of 1.

Atomic Ion:Atoms may be neutral or electrically charged. An atom that carries a positive or negative charge is called an atomic ion.

Isotopes: – Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons and electrons.

  • Isotopes – Element having equal number of Atomic Number (Z)
  • Example of isotopes: – Hydrogen has three isotopes. Hydrogen-1 (protium), hydrogen-2 (deuterium), and hydrogen-3 (tritium).
    1. Protium or hydrogen-1:- This isotope of hydrogen contains 1 proton, 1 electron, and no neutrons.
    2. Deuterium or hydrogen-2:- This isotope of hydrogen contains 1 proton, 1 electron, and 1 neutron.
    3. Tritium or hydrogen -3: – This isotope of hydrogen contains 1 proton, 1 electron, and 2 neutrons.
  • Uranium also has three isotopes in nature = 238U, 235U and 234U.

Isobars:Atoms of chemical elements having same atomic mass but a different atomic number are called Isobars.

The number of protons and neutrons alone will vary but the number of nucleons or the sum of protons and neutrons in isobars will always be same. Isobars always have different atomic structure because of the difference in atomic numbers.

  • Examples of Isobars:-
    • 18Ar4019K40 20Ca40 
    • 11Na2412Mg24
    • 26Fe5827Ni58 

Isotones: Isotones are those atoms which have the same number of neutrons (N) but different number of protons.

  • Example of isotones:-  3616S, 3717Cl, 3818Ar, 3919K, and 4020Ca
  • These all isotones of 20, because they all contain 20 neutrons.

Isomers: – Isomers have the same chemical formula but different chemical structures. Isomers contain the same number of atoms for each element, but properties and the atomic arrangement differs of atoms in the molecule.

Photo Electric Effect: – Photo-electric effect is the phenomenon of emission of electrons from the surfaces of certain substances, mainly metals, when light of shorter wavelength is incident upon them.

  • The photoelectric currents directly proportional to the intensity of incident radiation.

Threshold Frequency: – Threshold frequency is the minimum frequency, that capable of producing photoelectric effect.

Molecule: A molecule is defined as two or more atoms of the same element or different element that are bound together.

  • Molecules are made up of groups of atoms.
  • A molecule may be mononuclear or heteronuclear type.

Mononuclear: – It consists of atoms of one chemical element. For example – oxygen (O2).

Heteronuclear:A chemical compound composed of more than one element is type of Heteronuclear. For example: – water (H2O).

Avogadro Law: Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules. Avogadro made a distinction between atoms and molecule.

Avogadro’s number: Avogadro’s number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance.

  • It is equal to 6.022×1023 mol-1.
  • It is expressed by the symbol NA.

Matter: Anything which has mass and occupies space is called “matter”.

  • Everything around us, for example, book, pen, pencil, water, air, all living beings etc. are composed of matter.
  • Matter can exist in three physical states: – Solid, Liquid and Gas.
    1. Solids have definite volume and definite shape.
    2.  Liquids have definite volume but not the definite shape. They take the shape of the container in which they are placed.
    3. Gases have neither definite volume nor definite shape. They completely occupy the container in which they are placed.

These three states of matter are interconvertible by changing the conditions of temperature and pressure.

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Atomic and Nuclear Physics

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