Chem Bohr Model Quiz Review

In an emission spectrum, the emitted light appears as very thin, colored lines at very specific wavelengths. These wavelengths are discrete. What does this mean? Relate this observation to the Bohr model of the atom. What makes these wavelengths "discrete?"

"Discrete" refers to wavelengths that are fixed. The wavelengths are discrete/fixed due to the restrictions on energy levels. Since n can only be equal to whole numbers, the differences in energy between two levels are constant. For example, the emission of light at a result of a transition from n=2 → n=1 has a discrete/fixed value, since the energy of each orbit is fixed. Therrefore, the wavelengths corresponding to these energy values are also fixed.

The observed wavelength of red light is approximately 720 nm. Calculate the emission energy (in J) associated with this wavelength. (1m = 109 nm)

720 nm = 7.20x10-7 m E = hc/λ E = 2.76x10-19 J

Explain what is meant by "absorption". What is the sign of ΔE for this process?

Absorption is when an electron in an atom is promoted from a low energy level to a higher energy level. ΔE of the electron is positive, since the energy is increasing.

As n increases, what happens to the difference between two successive energy levels (ΔE)?

As n increases, the difference between two successive energy levels decreases.

As n increases, what happens to the energy of the corresponding orbit (En)?

As n increases, the energies of the orbits increase.

As ΔE increases, what happens to the wavelength of emitted light?

As ΔE increases, the wavelength of emitted light decreases. Remember that energy and wavelength are inverse to each other.

Are energy and frequency directly related, or inversely related?

Direct

Explain what is meant by "emission". What is the sign of ΔE for this process?

Emission is when an electron in an atom falls from a high energy level to a lower energy level, resulting in the emission of a photon. ΔE of the electron is negative, since the electron's energy is decreasing.

Are frequency and wavelength directly related, or inversely related?

Inverse

The Bohr model is sufficient for describing what physical phenomenon?

Light emission

What did Rutherford's model of the atom (the nuclear model) fail to describe? (hint: think about Coulomb's Law).

Rutherford's nuclear model of the atom failed to explain why the electrons in an atom are not absorbed by the nucleus. We would expect this to happen, since the nucleus and electron and oppositely-charged, and the electron is so small compared to the massive nucleus.

Which of these processes will emit light with the shortest wavelength? n = 1→ n = 7, n= 2→ n = 1, or n = 3 →n = 2?

Shortest wavelength = greatest energy. n=2 → n=1

Why is the energy gap between n = 1 and n = 2 larger than the energy gap between n = 2 and n = 3. Be specific in your answer.

The energy gap between n = 1 and n = 2 is greater because the electron is closer to the nucleus in n = 1 than in n = 2. Since the electron is closer to the nucleus, the nucleus is attracting the electron with greater force. Therefore, it takes more energy to get the electron to escape to a higher energy level.

A photon that is emitted from an atom is emitted with an energy of 2.51x10-19 J. Calculate the wavelength of this photon in meters and nanometers. (1m = 109 nm)

Use E = hc/λ, since this equation relates energy and wavelength. . λ = 7.92x10-7 m = 792 nm

A photon has a frequency of 6.00x104 Hz. What is the energy of this photon in J and kJ?

Use Ephoton = h * f, since this equation relates Energy (E) and Frequency (f). Ephoton = 3.98x10-29 J = 3.97x10-32 kJ

A photon has a frequency of 4.10x105 Hz. What is the wavelength of this photon in meters and nanometers? (1m = 109 nm)

Use c = f * λ, since this equation relates Frequency (f) and Wavelength (λ) . λ = 732 m = 7.32x1011 nm

Which of these processes will emit light with the greatest energy: n = 1→ n = 7, n= 2→ n = 1, or n = 3 →n = 2?

n=2 → n=1 will emit light with the greatest energy. n=1 → n=7 represents absorption, not emission. The energy gap between n=1 and n=2 is greater than the energy gap between n=2 and n=3.

Which of these processes will emit light with the greatest energy: n = 2 → n = 1, .n = 3 → n = 1, or n = 4 → n = 1?

n=4 → n=1, because the electron is falling all the way from n=4 to the ground state (n=1).