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Class 11 chap 2 | Atomic Structure 02 | Bohr's Atomic ModeL | Most Important For IIT JEE and NEET ||

Physics Wallah - Alakh Pandey・56 minutes read

The Bohr Atomic Model introduces fixed circular orbits for electrons, quantized angular momentum, and specific energy levels in atoms. It explains electron excitation, energy transitions between shells, and the atomic spectrum puzzle, emphasizing the importance of energy matching for smooth transitions between energy levels.

Insights

  • Bohr's Atomic Model introduces fixed circular orbits for electrons, emphasizing quantized angular momentum and specific energy levels, revolutionizing the understanding of atomic structure.
  • The model's explanation of electron excitation and de-excitation clarifies how energy gain or loss leads to transitions between energy levels, elucidating the atomic spectrum's line phenomenon and the necessity of precise energy matching for electron movement.

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Recent questions

  • What is the Bohr Atomic Model?

    The Bohr Atomic Model is a crucial concept in physics, particularly for Class 11th and 12th students, NEET exams, and general physics understanding.

  • How do electrons move in Bohr's model?

    In Bohr's model, electrons move in fixed circular orbits with specific energy and velocity, unlike Rutherford's model.

  • What is the Quantization Condition in Bohr's model?

    The Quantization Condition in Bohr's model states that the angular momentum of an electron is an integral multiple of h/2π, emphasizing specific orbits.

  • What provides the centripetal force in Bohr's model?

    The electrostatic force between the nucleus and electron provides the necessary centripetal force for the electron's circular motion in Bohr's model.

  • How does the Bohr model explain electron excitation?

    The Bohr model explains electron excitation as the gain of energy leading to movement to a higher energy level, while energy loss results in moving to a lower energy level within the same shell, addressing the conditions for electron excitation and de-excitation.

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Summary

00:00

Bohr Atomic Model: Crucial for Physics

  • Bohr Atomic Model is crucial for Class 11th and 12th, NEET, and Physics.
  • Bohr's model focuses on fixed circular orbits for electrons, unlike Rutherford's model.
  • The model emphasizes that electrons revolve in specific orbits with fixed energy and velocity.
  • The Quantization Condition in Bohr's model states that angular momentum is an integral multiple of h/2π.
  • The shell number (n) denotes the orbit in which the electron revolves.
  • Angular momentum (L) is a vector quantity equal to r x p, where r is the radius and p is momentum.
  • The angular momentum of an electron is quantized and must be an integral multiple of h/2π.
  • The electrostatic force between the nucleus and electron provides the centripetal force for the electron's circular motion.

15:48

"Electrostatic Force, Centripetal Force, and Bohr Model"

  • The electrostatic force between two charged particles is crucial in providing centripetal force.
  • The force between the nucleus and the electron is determined by the electrostatic force.
  • The formula for the force between two charges is 1/4πε₀ * q₁ * q₂ / r².
  • The constant in the formula is 1/4πε₀.
  • The force between opposite charges is attractive, while between similar charges, it is repulsive.
  • Centripetal force is essential for a rotating particle with mass 'm', radius 'r', and velocity 'v'.
  • The formula for centripetal force is mv²/r.
  • The Bohr model introduces the concept of stationary energy levels in atoms.
  • Electrons in fixed orbits have specific energies and cannot gain or lose energy.
  • Calculations in the Bohr model involve determining the radius, velocity, kinetic energy, potential energy, and total energy of an electron in a specific shell.

30:31

Electron Shell Formulas for JE Exams

  • The formula for the radius of an electron in a shell is r = n * h / (pi * m * z).
  • The radius of an electron in a shell is calculated as 0.53 * n / z angstrom.
  • The shortcut formula for the radius of a shell is r = 0.53 * n / z angstrom.
  • The Bohr model is not valid for all atoms, only for single electron species.
  • The velocity of an electron in a shell is v = 2.18 * 10^6 * z / n meters per second.
  • The speed of an electron in the first orbit of hydrogen is 2.18 * 10^6 meters per second.
  • The energy of an electron in a shell consists of kinetic energy and electrostatic potential energy.
  • The formula for kinetic energy of an electron is 1/8 * m * z^2 * e^4 / (4 * h * n^2).
  • The constants in the expression for kinetic energy are the mass of the electron, charge of the electron, Planck's constant, and the shell number.
  • It is essential to understand the basics thoroughly for JE Mains and JE Advanced exams.

46:00

Energy Levels and Electron Excitation in Atoms

  • The value obtained after putting the values of z, s, b, n, and s is 13.6 electron volts.
  • The kinetic energy of an electron in the ith shell of an atom with atomic number z changes according to the formula 13.6 * z * s / n.
  • The potential energy between two charged particles q1 and q2 at a distance r is calculated using the formula 1/4 * pi * n * q1 * q2 / r.
  • The potential energy between an electron and a nucleus is calculated as -2 * 13.6 in joules per square electron volt.
  • The total energy of an electron in a shell is the sum of potential and kinetic energy, resulting in -13.6 * z * s in joules per square electron volt.
  • The negative total energy of an electron indicates its bound state to the nucleus due to ionization energy requirements.
  • The total energy of an electron in different shells of a hydrogen atom varies, with the first shell having -13.6 electron volts, the second -3.4, the third -1.51, and the fourth 0.85.
  • As the electron moves away from the nucleus, its energy increases, with the maximum energy being zero when the electron is free from the nucleus.
  • Excitation of an electron occurs when it gains energy and moves to a higher energy level, while losing energy results in moving to a lower energy level within the same shell.
  • The Bohr model explains the conditions for electron excitation and de-excitation, emphasizing that energy gain or loss leads to movement between energy levels rather than within a shell.

01:01:20

Electron Energy Levels Determine Shell Movement

  • B6's total energy will be affected by not gaining 4.6 electron volts, leading to a change in its energy level.
  • Electrons require specific energy levels to move to different shells, akin to seating arrangements based on energy values.
  • Providing energy to an electron alters its energy level, prompting it to move to a shell with a matching energy value.
  • Electrons only accept energy that aligns with specific energy levels, ensuring they transition smoothly between shells.
  • Bohr's model addressed the atomic spectrum puzzle by explaining how electrons absorb selective energies, resulting in the observed line spectrum phenomenon.
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