Careers360 Logo
Planck's quantum theory

Planck's quantum theory

Edited By Shivani Poonia | Updated on Jul 02, 2025 05:49 PM IST

Introduction to Planck's Quantum in Chemistry:

At the end of the 19th century, scientists were curious about Black body radiation, a black body radiation means an idealized material that absorbs almost all types of electromagnetic radiation. No clues were identified with classical physics principles, how did this black body emit energy? According to classical physics, the emitted energy should increase with the increase in the frequency, this phenomenon is known as ultraviolet catastrophe, and the actual experimental results were contradictory. In 1900, German physicist Max Planck proposed the revolutionary theory, which today we study as Planck's Quantum theory. This theory gave the groundwork for Quantum physics. According to Planck's hypotheses, the energy emitted or absorbed by the body (e.g., Black body radiation) is in discrete or specific values, not random arbitrary values. He called it quantized values. From here comes another in quantum mechanics.

This Story also Contains
  1. Introduction to Planck's Quantum in Chemistry:
  2. Quantization of Energy - Why Energy Comes in Bits?
  3. Conclusion
Planck's quantum theory
Planck's quantum theory

In this article, we will cover the concept of Planck's quantum theory. This concept falls under the broader category of Atomic structure, which is a crucial chapter in Class 11 chemistry. It is not only essential for board exams but also for competitive exams like the Joint Entrance Examination (JEE Main), National Eligibility Entrance Test (NEET), and other entrance exams such as SRMJEE, BITSAT, WBJEE, BCECE, and more.

Quantization of Energy - Why Energy Comes in Bits?

When the energy is emitted and absorbed in discrete quantities, these discrete quantities are called Quanta, which is the quantization of energy. This term was later termed photons by Albert Einstein.

In short, we can say that atoms and molecules could emit (or absorb) energy only in discrete quantities known as quanta and not continuously. The following are certain phenomena that could not be explained by the wave nature of electromagnetic radiation and are explained by the particle nature:

Line spectra of atoms with special reference to hydrogen.

Max Planck suggested that the energy that is emitted or absorbed by the black body is not continuous but discontinuous in the form of small discrete packets of energy. Each such packet of energy is called a ‘quantum’. In the case of light, the quantum of energy is called a ‘photon’. The energy of radiation is proportional to its frequency ((ν)) and is expressed by the following equation:

E=hν=hcλ

where h is the Planck's constant, and it has a value equal to 6.63 × 10-34 J-s

Let's try to solve the question based on the above formula,

Recommended topic video on ( Plank Quantum Theory)


Example 1: The nature of emission of radiation from hot bodies (black-body radiation).

Which one of the following is not characteristic of Planck's quantum theory of radiation

1) The energy is not absorbed or emitted in whole numbers or multiple quantums.

2)Radiations are associated with energy.

3) Radiation energy is not emitted or absorbed continuously but in the form of small packets called quanta.

4) This magnitude of energy associated with a quantum is proportional to the frequency.

Solution:

According to Plank's Quantum Theory,

Energy is absorbed or emitted not in a continuous manner, but in the form of small packets called Quanta.

The energy associated with the quanta is proportional to the frequency.

Hence, the answer is the option (1).

1. Ejection of electrons from a metal surface when radiation strikes it (photoelectric effect).

2. Variation of heat capacity of solids as a function of temperature.

Example 2: Which of the following statements is false?

1) Photon has momentum as well as wavelength.

2) The splitting of spectral lines in an electrical field is called the Stark effect.

3) The Rydberg constant has a unit of energy

4) (correct) The frequency of emitted radiation from a black body goes from a lower wavelength to a higher wavelength as the temperature increases.

Solution

As we learned in

The energy (E) of a quantum of radiation -

E=hv

Where h is plank's constant and ν is the frequency

When the temperature is increased, the black body emits high-energy radiation, from a higher wavelength to a lower wavelength.

Hence, the answer is an option (4).

Example 3:The energy of one quantum of light with a wavelength of 6500 Ao (1 Ao = 10-10m) is

1) 5 x 10-18J

2) (correct) 3.06 x 10-19J

3) 8.02 x 10-20J

4)9.0 x 10-24J

Solution

As we learn

Planck’s Quantum Theory -

Atoms and molecules could emit (or absorb) energy only in discrete quantities known as quanta, and not continuously.

The energy of one quantum of light

E=hcλ=6.62×10−34×3×1086.5×10−7=3.06×10−19 J

Hence, the answer is the option (2).

Example 4: According to Planck's quantum theory, the energy of a quantum of radiation is given by:

1) E=hv
2) E=hcλ
3) E=hc2λ
4) E=hλ

According to Planck's quantum theory, the energy of a quantum of radiation is directly proportional to its frequency. This is given by the equation E=hv, where E is the energy of the quantum, h is Planck's constant (6.626×10−34 J s), and v is the frequency of the radiation.

Hence, the answer is the option (1).

Example 5: What is the wavelength of a photon with energy 3.0×10−19 J, according to Planck's quantum theory?
1) 1.15×10−7 m
2) (correct) 2.50×10−7 m
3) 5.56×10−7 m
4) 9.23×10−7 m

Solution

According to Planck's quantum theory, the energy of a photon is given by the equation E=hcλ, Where E is the energy of the photon, h is Planck's con (6.626×10−34 Js),cis thed the speed of light (3.0×108 m/s)(3.0×108 m/s)λ is the wavelength of the photon.

Rearranging this equation gives
λ=hcE

Plugging in the given values, we get
λ=(6.626×10−34 J s)(3.0×108 m/s)3.0×10−19 J≈2.50×10−7 m

Hence, the answer is the option (2).

Conclusion

We can conclude that Planck's quantum theory gave a whole new perspective and also a whole new paradigm shift in science, and we understood energy absorption and emission. The black body radiation which was initially not cleared by classical physics is much clearer in Quantum mechanics. Planck's postulate or Planck's Hypothesis explains the energy emitted and absorbed are in discrete quantities and termed as Quantization of energy and the term quanta termed Photons by Albert Einstein. The nature of emission or absorption of radiation from hot bodies (black-body radiation). The ejection of electrons from a metal surface when radiation strikes it called the photoelectric effect. Line spectra of atoms with special reference to hydrogen(Bohr's model of hydrogen).

Frequently Asked Questions (FAQs)

1. What is the Black Body Radiation?

Any ideal body can absorb almost all types of electromagnetic radiation.

2. Name the scientist who gave the Quantum Theory.

In 1900, German physicist Max Planck proposed the revolutionary theory, which today we study as Planck's Quantum theory.

3. What is a Photon?

Photons are the discrete energy emitted or absorbed by any object. Earlier, this term was known as Quanta, which was later termed Photons by Albert Einstein.

4. How is the energy of a quantum of radiation related to its frequency?

The energy of a quantum of radiation is directly proportional to its frequency.

5. In which year did Max Planck win the Nobel Prize for his revolutionary work in the field of Quantum mechanics?

In 1918 Max Planck won the Nobel Prize for his revolutionary work in the field of Quantum mechanics.

6. What is Planck's quantum theory?
Planck's quantum theory states that energy is emitted or absorbed by matter in discrete packets called quanta, rather than as a continuous wave. This revolutionary idea challenged classical physics and laid the foundation for quantum mechanics.
7. Why did Planck propose the quantum theory?
Planck proposed the quantum theory to explain the emission spectrum of blackbody radiation, which classical physics could not accurately describe. His theory resolved the "ultraviolet catastrophe" and matched experimental observations.
8. What is a quantum of energy?
A quantum of energy is the smallest, indivisible unit of energy that can be emitted or absorbed by matter. It is proportional to the frequency of the radiation and is given by E = hν, where h is Planck's constant and ν is the frequency.
9. How does Planck's constant relate to quantum theory?
Planck's constant (h) is a fundamental physical constant that relates the energy of a photon to its frequency. It appears in the equation E = hν and represents the scale at which quantum effects become significant.
10. What is the significance of Planck's quantum theory in atomic structure?
Planck's quantum theory led to the development of the Bohr model of the atom, which explained discrete electron energy levels and spectral lines. It revolutionized our understanding of atomic structure and electron behavior.
11. What is the wave-particle duality in quantum theory?
Wave-particle duality, a concept stemming from Planck's work, suggests that all matter and energy exhibit both wave-like and particle-like properties. This dual nature is fundamental to quantum mechanics and challenges classical intuitions about physical reality.
12. How did Planck's theory influence the development of quantum mechanics?
Planck's theory was the first step towards quantum mechanics. It inspired further work by Einstein, Bohr, Schrödinger, and others, leading to the formulation of quantum mechanics as a comprehensive theory describing the behavior of matter and energy at the atomic and subatomic scales.
13. How does Planck's theory relate to the uncertainty principle?
Planck's theory introduced the concept of discrete energy quanta, which led to the development of the uncertainty principle. This principle states that certain pairs of physical properties, like position and momentum, cannot be simultaneously measured with arbitrary precision.
14. What is the significance of Planck's black body radiation law?
Planck's black body radiation law accurately describes the intensity of electromagnetic radiation emitted by a perfect absorber (black body) at different frequencies. It resolved the ultraviolet catastrophe and provided evidence for energy quantization.
15. What is the relationship between Planck's theory and the Bohr model of the atom?
Bohr incorporated Planck's quantum theory into his atomic model, proposing that electrons could only exist in discrete energy levels. This explained the stability of atoms and the discrete spectral lines observed in atomic emission spectra.
16. How does Planck's theory contribute to our understanding of chemical bonding?
Planck's theory underlies the quantum mechanical description of electron orbitals and energy levels, which is crucial for understanding chemical bonding. It explains why atoms form specific types of bonds and why molecules have particular shapes and properties.
17. How does Planck's theory relate to the concept of zero-point energy?
Zero-point energy, the lowest possible energy a quantum mechanical system can have, is a consequence of Planck's quantum theory. It suggests that even at absolute zero temperature, particles retain some motion due to quantum effects.
18. How does Planck's theory contribute to our understanding of chemical reactions?
Planck's theory underlies the quantum mechanical description of molecular orbitals and energy states, which is crucial for understanding chemical reactivity. It explains why certain reactions occur, how activation energy works, and the nature of transition states.
19. What is the significance of Planck's theory in understanding the periodic table?
Planck's theory is fundamental to understanding electron configurations and orbitals, which form the basis of the periodic table. It explains periodic trends in atomic properties and why elements in the same group have similar chemical behaviors.
20. How does Planck's theory relate to the concept of quantum tunneling?
Quantum tunneling, where particles can pass through energy barriers that classical physics forbids, is a consequence of the wave-like nature of matter described by quantum theory. Planck's work laid the foundation for understanding such counterintuitive quantum phenomena.
21. What is the role of Planck's theory in understanding spectroscopy?
Planck's theory is fundamental to spectroscopy, explaining why atoms and molecules absorb and emit light at specific frequencies. It provides the theoretical basis for interpreting spectral data and identifying chemical compounds based on their unique spectral signatures.
22. How does Planck's theory contribute to our understanding of chemical bond energies?
Planck's theory underlies the quantum mechanical description of chemical bonds. It explains why bond energies are quantized and helps predict the strength and behavior of chemical bonds based on the electronic structure of atoms and molecules.
23. How does Planck's theory relate to the concept of quantum superposition?
Quantum superposition, where a system can exist in multiple states simultaneously until measured, is a consequence of the wave-like nature of matter described by quantum theory. Planck's work laid the groundwork for understanding such non-classical behavior of quantum systems.
24. What is the connection between Planck's theory and the concept of quantum entanglement?
While Planck's theory doesn't directly describe quantum entanglement, it laid the foundation for quantum mechanics, which predicts and explains entanglement. This phenomenon, where particles become correlated in ways that can't be explained by classical physics, is a key feature of quantum systems.
25. How does Planck's theory contribute to our understanding of chemical equilibrium?
Planck's theory underlies the quantum mechanical description of molecular energy states, which is crucial for understanding chemical equilibrium. It explains why equilibrium constants have specific values and how temperature affects equilibrium positions.
26. What is the role of Planck's theory in explaining the behavior of electrons in conductors and semiconductors?
Planck's theory is fundamental to understanding the band theory of solids, which explains the electronic properties of conductors and semiconductors. It helps describe how electrons occupy energy bands and how this affects a material's electrical conductivity.
27. What is the role of Planck's theory in understanding the Franck-Condon principle?
The Franck-Condon principle, which explains the intensity of vibronic transitions in molecules, is based on the quantum mechanical nature of molecular vibrations described by Planck's theory. It helps interpret the structure of electronic absorption and emission spectra.
28. How does Planck's theory relate to the concept of spin in quantum mechanics?
While Planck's theory doesn't directly describe spin, it laid the groundwork for the development of quantum mechanics, which includes spin as an intrinsic property of particles. Spin is quantized, aligning with the discrete nature of quantum properties proposed by Planck.
29. How does Planck's theory contribute to our understanding of chemical kinetics?
Planck's theory underlies the quantum mechanical description of molecular collisions and transitions states in chemical reactions. It helps explain reaction rates, activation energies, and the temperature dependence of reaction kinetics at a fundamental level.
30. What is the significance of Planck's theory in explaining the phenomenon of quantum tunneling in chemical reactions?
Quantum tunneling, where particles can pass through energy barriers that classical physics forbids, is explained by the wave-like nature of matter described in quantum theory. This phenomenon is important in understanding certain chemical reactions, especially at low temperatures.
31. How does Planck's theory relate to the concept of quantum confinement in nanomaterials?
Quantum confinement, observed in nanomaterials when particle size approaches the de Broglie wavelength, is a direct consequence of the quantum mechanical nature of matter described by Planck's theory. It explains size-dependent properties of nanomaterials.
32. What is the role of Planck's theory in understanding the behavior of electrons in chemical bonds?
Planck's theory is crucial for understanding the quantum mechanical nature of chemical bonds. It explains why electrons in bonds occupy specific molecular orbitals, why bond energies are quantized, and how this leads to the observed properties of molecules.
33. How does quantum theory explain the stability of atoms?
Quantum theory explains atomic stability by describing electrons in discrete energy levels or orbitals. Electrons can only exist in these specific energy states, preventing them from spiraling into the nucleus as classical physics would predict.
34. What is the relationship between Planck's theory and the photoelectric effect?
Einstein used Planck's quantum theory to explain the photoelectric effect, proposing that light consists of discrete particles (photons) with energy E = hν. This connection further validated Planck's ideas and extended quantum concepts to light.
35. How does Planck's theory differ from classical physics?
Planck's theory introduces discreteness in energy exchanges, contrasting with classical physics' continuous energy model. It also implies a fundamental limit to the precision with which certain pairs of physical properties can be known simultaneously.
36. What is the quantization of energy?
The quantization of energy refers to the idea that energy can only be emitted or absorbed in discrete amounts (quanta), rather than continuously. This concept is central to Planck's quantum theory and contradicts classical physics' continuous energy model.
37. How does Planck's theory explain atomic spectra?
Planck's theory, when applied to atoms, explains why atomic spectra consist of discrete lines rather than continuous spectra. Electrons transitioning between quantized energy levels emit or absorb specific frequencies of light, producing characteristic spectral lines.
38. What is the Planck-Einstein relation?
The Planck-Einstein relation, E = hν, connects the energy (E) of a photon to its frequency (ν) through Planck's constant (h). This fundamental equation bridges the concepts of energy quantization and wave-particle duality.
39. How does Planck's theory explain the photoelectric effect?
Planck's theory, as applied by Einstein to the photoelectric effect, explains why the emission of electrons from a metal surface depends on the frequency of incident light, not its intensity. Each photon carries a discrete amount of energy, E = hν, which must exceed the work function to eject an electron.
40. What is the connection between Planck's theory and the wave function in quantum mechanics?
Planck's theory laid the groundwork for the development of wave functions in quantum mechanics. The wave function, which describes the quantum state of a system, incorporates the idea of quantized energy levels and probabilistic behavior of particles.
41. How does Planck's theory explain the discrete nature of atomic energy levels?
Planck's theory suggests that energy can only be absorbed or emitted in discrete amounts. When applied to atoms, this explains why electrons can only occupy specific energy levels, resulting in the discrete nature of atomic energy states.
42. What is the significance of Planck's theory in understanding molecular spectra?
Planck's theory helps explain the complex spectra of molecules. The quantized energy levels in molecules, including electronic, vibrational, and rotational states, result in characteristic spectral lines that can be used to identify and study molecular structures.
43. What is the role of Planck's theory in explaining the behavior of electrons in atoms?
Planck's theory explains why electrons in atoms can only exist in specific energy states and cannot spiral into the nucleus. It provides the foundation for understanding electron transitions, atomic stability, and the emission and absorption of light by atoms.
44. What is the relationship between Planck's theory and the Heisenberg uncertainty principle?
Planck's theory introduced the concept of quantization, which led to the development of the uncertainty principle. This principle states that certain pairs of physical properties, like position and momentum, cannot be simultaneously measured with arbitrary precision, a direct consequence of the wave-like nature of matter proposed in quantum theory.
45. How does Planck's theory explain the discrete emission spectrum of hydrogen?
Planck's theory, when applied to the hydrogen atom, explains why its emission spectrum consists of discrete lines. Electrons transitioning between quantized energy levels emit photons with specific energies, resulting in the characteristic spectral lines of hydrogen.
46. What is the connection between Planck's theory and the Schrödinger equation?
Planck's theory provided the conceptual basis for the Schrödinger equation, which describes how the quantum state of a physical system changes over time. The equation incorporates the idea of quantized energy levels and wave-particle duality.
47. How does Planck's theory explain the stability of electron orbitals?
Planck's theory, by introducing quantized energy levels, explains why electrons in atoms occupy specific orbitals and don't collapse into the nucleus. Electrons can only exist in these discrete energy states, ensuring the stability of atomic structures.
48. What is the significance of Planck's theory in explaining the photoelectric effect's threshold frequency?
Planck's theory, as applied by Einstein to the photoelectric effect, explains the existence of a threshold frequency. Below this frequency, no electrons are emitted regardless of light intensity, as individual photons lack sufficient energy to overcome the work function of the metal.
49. How does Planck's theory relate to the concept of quantum numbers?
Quantum numbers, which describe the state of electrons in atoms, are a direct consequence of the quantization of energy proposed by Planck. These numbers (n, l, ml, ms) arise from solving the Schrödinger equation, which is based on quantum principles.
50. What is the significance of Planck's theory in understanding molecular orbital theory?
Planck's theory provides the foundation for molecular orbital theory, which describes the behavior of electrons in molecules. It explains why molecular orbitals have specific energies and shapes, and how they contribute to molecular properties and reactivity.
51. How does Planck's theory explain the discrete nature of vibrational and rotational energy levels in molecules?
Planck's theory, when applied to molecular motion, explains why vibrational and rotational energy levels are quantized. This quantization results in discrete spectral lines in infrared and microwave spectroscopy, allowing for detailed analysis of molecular structures.
52. How does Planck's theory contribute to our understanding of quantum dots?
Quantum dots, nanoscale semiconductor particles, exhibit properties that can be explained by Planck's quantum theory. The discrete energy levels in quantum dots, which depend on their size, are a direct consequence of quantum confinement effects predicted by the theory.
53. What is the significance of Planck's theory in explaining the phenomenon of fluorescence?
Planck's theory explains the quantized nature of electronic transitions involved in fluorescence. It helps describe why certain materials absorb light at one wavelength and emit it at another, and why these emissions occur at specific energies.
54. What is the role of Planck's theory in understanding the quantum mechanical model of the atom?
Planck's theory is fundamental to the quantum mechanical model of the atom. It explains the discrete energy levels of electrons, the probabilistic nature of their locations (orbitals), and the quantized angular momentum of electrons in atoms.
55. How does Planck's theory contribute to our understanding of photochemical reactions?
Planck's theory explains the quantized nature of light absorption in photochemical reactions. It helps describe why specific wavelengths of light can initiate certain reactions, and how the energy of absorbed photons relates to chemical transformations.

Articles

Back to top