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The "size" of the atom in Rutherford's model is about \(1.0 \times 10^{-10} \mathrm{~m} .\) (a) Determine the speed of an electron moving about the proton using the auractive electrostatic force between an electron and a proton separated by this distance. (b) Does this speed suggest that Einsteinian relativity must be considered in studying the atom? (c) Compute the de Broglie wavelength of the electron as it moves about the proton. (d) Does this wavelength suggest that wave effects, such as diffraction and interference, must be considered in studying the atom?

Short Answer

Expert verified
The speed of the electron is not close enough to the speed of light to necessitate considerations under special relativity. However, the de Broglie wavelength of the electron is comparable to the size of the atom, which suggests that wave effects must be considered in studying the atom.

Step by step solution

01

Calculation of Electron Speed

Use the formula for electrostatic force \(F = \frac{{k \cdot |q1| \cdot |q2|}}{{r^2}}\), where \(F\) is the force, \(k\) is Coulomb's constant, \(q1\) and \(q2\) are the magnitudes of the charges, and \(r\) is the distance between the charges. Here the attractive electrostatic force provides the centripetal force for the electron. Thus, \(F = m \cdot v^2 / r\), where \(m\) is mass and \(v\) is velocity (or speed in this context). By equating these two expressions, we can solve for \(v\).
02

Relativity Assessment

After finding the speed of the electron in step 1, check if the speed is comparable to the speed of light (approximately \(3 \times 10^8\) m/s). If the electron's speed is a significant fraction of the speed of light, the relativistic effects must be accounted for. Compare the two speeds to make this determination.
03

De Broglie Wavelength Calculation

After determining the speed, calculate the de Broglie wavelength of the electron using the equation \(\lambda = h / (m \cdot v)\), where \(h\) is Planck's constant. The mass and speed of the electron were either given or calculated in previous steps.
04

Wave Effects Assessment

After the wavelength has been found, compare it with the size of the atom. If the wavelength is comparable to or larger than the size of the atom, wave effects such as diffraction and interference must be considered.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electrostatic Force
The electrostatic force is a fundamental concept in understanding how electrons and protons interact within an atom, particularly in the Rutherford model. This force is attractive and arises from the electric charges of the electron and the proton. It's calculated using Coulomb’s Law:
  • Formula: \( F = \frac{{k \cdot |q_1| \cdot |q_2|}}{{r^2}} \)
  • \( F \) represents the force
  • \( k \) is Coulomb's constant, approximately \( 8.99 \times 10^9 \) N·m²/C²
  • \( q_1 \) and \( q_2 \) are the charges of the proton and electron, respectively
  • \( r \) is the separation distance, \( 1.0 \times 10^{-10} \) m in this case
In this model, the electrostatic force acts as the centripetal force, keeping the electron in its orbit around the proton. By equating the electrostatic force with the centripetal force (\( F = m \cdot v^2 / r \)), where \( m \) is the electron's mass and \( v \) is its speed, we can solve for \( v \). Understanding this interaction is crucial in predicting how the electron behaves in its orbit.
de Broglie Wavelength
The de Broglie wavelength is an essential concept that combines classic physics with modern quantum mechanics. It reflects the wave-like nature of particles, such as electrons. This wavelength is calculated using the formula:
  • \( \lambda = \frac{h}{m \cdot v} \)
  • \( \lambda \) is the de Broglie wavelength
  • \( h \) is Planck’s constant, approximately \( 6.626 \times 10^{-34} \) J·s
  • \( m \) is the particle's mass
  • \( v \) is its velocity
After finding the electron's speed, you can compute \( \lambda \). If the wavelength is comparable to the size of the atom, this indicates that the wave properties of electrons, such as interference and diffraction, need to be considered. The concept of the de Broglie wavelength bridges the gap between particle motion and wave behavior, impacting how we perceive atomic structures.
Relativistic Effects
Relativistic effects become significant when the speeds involved approach the speed of light. When considering an electron moving around a proton, if its speed is a substantial fraction of the speed of light (\( c = 3 \times 10^8 \text{ m/s} \)), relativistic physics must be applied.
Here’s what you should think about:
  • If \( v \) (electron's speed) is close to \( c \), relativistic mass increase and time dilation might influence the electron's behavior.
  • For the electron in a typical atom at the size \( 1.0 \times 10^{-10} \text{ m} \), these effects are usually negligible - classic mechanics are sufficient.
However, in high-energy physics, such as in accelerators where particles approach light speed, these effects are crucial. Understanding when relativistic adjustments are needed helps in accurately modeling electron behavior in varying contexts.
Wave-Particle Duality
Wave-particle duality is a fundamental principle of quantum mechanics that posits particles, like electrons, exhibit properties of both particles and waves. This duality is prominently described by:
  • Electrons behaving like particles in collision experiments.
  • Wave-like behavior evident from diffraction and interference patterns observed in double-slit experiments.
The de Broglie wavelength of an electron supports this dual nature. When the wavelength is similar in magnitude to the atomic size, wave effects have noticeable implications, such as interferometric patterns. This duality challenges classic physics, which treats particles and waves as separate entities. Accepting this concept enhances the understanding of phenomena at the quantum level, where particles can spread over space like waves while still maintaining particle-like properties in interactions.

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Most popular questions from this chapter

Using the concept of standing waves, de Broglie was able to derive Bohr's stationary orbit postulate. He assumed a confined electron could exist only in states where its de Broglie waves form standing-wave patterns, as in Figure \(28.6 .\) Consider a particle confined in a box of length \(L\) to be equivalent to a suring of length \(L\) and fixed at both ends. Apply de Broglic's concept to show that (a) the linear momentum of this particle is quantized with \(p=m \tau=n h / 2 L\) and \((b)\) the allowed states correspond to particle energies of \(E_{u}=n^{2} E_{0}\) where \(E_{0}=h^{2} /\left(8 m L^{2}\right)\).

List the possible sets of quantum numbers for electrons in the \(3 d\) subshell.

Two electrons in the same atom have \(n=3\) and \(\ell=1\). (a) List the quantum numbers for the possible states of the atom. (b) How many states would be possible if the exclusion principle did not apply to the atom?

An electron has a de Broglie wavelength equal to the diameter of a hydrogen atom in its ground state. (a) What is the kinetic energy of the electron? (b) How does this energy compare with the ground-state energy of the hydrogen atom?

(a) Write an expression relating the kinetic energy \(K E\) of the electron and the potential energy \(P E\) in the Bohr model of the hydrogen atom. (b) Suppose a hydrogen atom absorbs a photon of energy \(E\), resulting in the transfer of the electron to a higher-energy level. Express the resulting change in the potential energy of the system in terms of \(E\). (c) What is the change in the electron's kinetic encrgy during this process?

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