Quiz 8

12. What is a photon? How is the energy of a photon related to its wavelength? Its frequency?

A photon is a packet of light. The energy of the photon can be expressed in terms of wavelength as E=hc/λ or in terms of frequency as E=hv

23. What is a probability distribution map?

A probability distribution map is a statistical map that shows where an electron is likely to be found under a given set of conditions.

19. What is a trajectory? What kind of information do you need to predict the trajectory of a particle?

A trajectory is a path that is determined by the particle's velocity, its position, and the forces acting on it. Both position and velocity are required to predict trajectory.

13. What is an emission spectrum? How does an emission spectrum of a gas in a discharge tube differ from a white light spectrum?

An emission spectrum when an atom absorbs energy and reemits that energy as light. The light emitted contains distinct wavelengths for each element. The emission spectrum of a particular element is always the same and can be used to identify the element. A white light spectrum is continuous, meaning that there are no sudden interruptions in the intensity of the light as a function of wavelengths. It consists of all wavelengths. Emission spectra are not continuous. They consist of bright lines at specific wavelengths, with complete darkness in between.

11. How did the photoelectric effect lead Einstein to propose that light is quantized?

Because of the results of the experiments with the photoelectric effect, Einstein proposed that light energy must come in packets. The amount of energy in a light packet depends on its frequency. The emission of electrons depends on whether a single photon has sufficient energy to dislodge a single electron.

20. Why does the uncertainty principle make it impossible to predict a trajectory for the electron?

Because the uncertainty principle says that you cannot know both the position and velocity of the electron simultaneously, you cannot predict the trajectory.

17. What are complementary properties? How does electron diffraction demonstrate the complementarity of the wave nature and particle nature of the electron?

Complementary properties excludes one another. The more you know about one, the less you know about the other. Which of two complementary properties you observe depends on the experiment you perform. In electron diffraction, when you try to observe which hole the electron goes through, you lose the interference pattern. When you try to observe the interference pattern, you cannot determine which hole the electron goes through.

21. Newton's laws of motion are deterministic. Explain this statement.

Deterministic means that the present determines the future. That means that under the identical condition, identical results will occur.

9. Explain the wave behavior known as diffraction. Draw the diffraction pattern that occurs when light travels through two slits comparable in size and separation to the light's wavelength.

Diffraction occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. The wave bends around the slit. The diffraction of light through two slits separated by a distance comparable to the wavelength of the light results in an interference pattern. Each slit acts as a new wave source, and the two new waves interfere with each other. This results in a pattern of bright and dark lines.

15. Explain electron diffraction.

Electron diffraction occurs when an electron beam is aimed at two closely spaced slits and a series of detectors is arranged to detect the electrons after they pass through the slits. An interference pattern similar to that observed for light is recorded behind the slits. Electron diffraction is evidence of the wave nature of electrons.

5. What determines the color of light? Describe the difference between red light and blue light.

For visible light, wavelength determines the color. Red light has a wavelength of 750 nm, the longest wavelength of visible light, and blue has a wavelength of 500 nm.

18. Explain Heinsberg's uncertainty principle. What paradox is at least partially solved by the uncertainty principle?

Heinsberg's uncertaintu principle states that the product of Δx and mΔv must be greater than or equal to a finite number. In other words, the more accurately you know the position of an electron, the less accurately you can know its velocity and vise versa. The complementarity of the wave nature and particle nature of the electron results in the complementarity of velocity and position. Heinsberg solved the contradiction of an object as both a particle and a wave by introducing complementarity- an electron is observed as either a particle or a wave, but never both at once.

14. Describe the Bohr model for the atom. How did the Bohr model account for the emission spectra of atoms?

In the Bohr model, electrons travel around the nucleus in circular orbits. Bohr's orbits could exist only at specific, fixed distances from the nucleus. The energy of each orbit was also fixed, or quantized. Bohr called these orbits stationary states and suggested that although they obeyed the laws of classical mechanics. Bohr further proposed that in contradiction to classical electromagnetic theory, no radiation was emitted by an electron orbiting the nucleus in a stationary state. It was only when an electron jumped, or made a transition, from one stationary state to another that radiation was emitted or absorbed. The emission spectrum of an atom consisted of discrete lines because the stationary states existed only at specific, fixed energies. The energy of the photon created when an electron made a transition from one stationary state to another was simply the energy difference between the two stationary states.

2. What is light? How fast does it travel in a vacuum?

Light is electromagnetic radiation, a type of energy embodied in oscillating electric and magnetic fields. Light in a vacuum travels at 3.00x108 m/s

16. What is the de Broglie wavelength of an electron? What determines the value of the de Broglie wavelength for an electron?

The de Broglie wavelength is associated with an electron traveling through space. It is related to its kinetic energy. The wavelength, λ associated with an electron of mass, m, moving at velocity, v, is given by the de Broglie relation: λ=h/mv

4. Define the frequency of electromagnetic radiation. How is frequency related to wavelength?

The frequency is the number of cycles that pass through a stationary point in a given period of time. The units of frequency are cycles per second. The frequency is inversely proportional to wavelength. Frequency and wavelengths are related by the equation v= c/λ

22. An electron behaves in ways that are at least partially indeterminate. Explain this statement.

The indeterminate behavior of an electron means that under identical conditions, the electron does not have the same trajectory and does not land in the same spot each time.

10. Describe the photoelectric effect. How did experimental observations of this phenomenon differ from the predictions of classical electromagnetic theory?

The photoelectric effect was the observation that many metals emit electrons when light shines on them. Classical electromagnetic theroy attributed this effect to the transfer of energy from the light to an electron in the metal, dislodging the electron. In this description, changing either the wavelength or the amplitude of the light should affect the emission of electrons. So the rate at which electrons were emitted from a metal due to the photoelectric effect could be increased by using either light of shorter wavelength or light of higher intensity. Experiments showed that the light used to dislodge electrons has a threshold frequency below which no electrons were emitted from the metal, no matter how long the light shone on the metal. Low- frequency light would eject electrons even at low intensity without any lag time.

6. What determines the color of a colored object? Explain why grass appears green.

The presence of a variety of wavelengths in white light is responsible for the way we perceive colors in objects. When a substance absorbs some colors while reflecting others, it appears colored. Grass appears green because it reflects primarily the wavelength associated with green light and absorbs the others.

1. Why is the quantum-mechanical model of the atom important for understanding chemistry?

The quantum-mechanical model of the atom important because it explains how electrons exist in atoms and how those electrons determine the chemical and physical properties of elements.

3. Define the wavelength and amplitude of a wave. How are these related to the energy of the wave?

The wavelength of the wave is the distance in space b/w adjacent crests and is measured in units of distance. The amplitude of the wave is the vertical height of a crest. The more closely spaced the waves, the more energy there is. The amplitude of the electric and magnetic field waves in light determine the intensity or brightness of the light. The higher the amplitude is the more energy the wave has.

8. Explain the wave behavior known as interference. Explain the difference between constructive and destructive interference.

Waves interact with each other in a characteristic way called interference. They can cancel each other out or build each other up, depending on their alignment upon interaction. Constructive interference occurs when waves of equal amplitude from two sources are in phase and a wave with twice the amplitude results. Destructive interference occurs when the waves are completely out of phase and the waves cancel each other.

7. Give an approximate range of wavelengths for each type of electromagnetic radiation and summarize the characteristics and/or the uses of each. a. gamma rays b. X-rays c. ultraviolet d. visible light e. infrared radiation f. microwave radiation g. radio waves

a. gamma rays, wavelength range is 10-11 to 10-13m. produced by the sun, other stars, certain unstable atomic nuclei on Earth. human exposure to it is dangerous because of its high energy b. x-rays 10-8 to 10-11m. x-ray pass through substances that block visible light c. ulthra violet .4 x 10-6 to 10-8m sunburn alot of energy d. .75 x 10-6 to .4 10-3 e. 75x10-6 to 10-3 heat near object that hot is infrared. f. 10-3 to 10-1 g. 10-3 to 105.transmit signals (AM radio), tv, phones