Atoms quiz

Most alpha particles passed undeflected through gold foil because:

The radius of the first Bohr orbit of hydrogen is about:

The ground state energy of a hydrogen atom is:

The Balmer series lies in the:

According to Bohr, the angular momentum of an electron in the nth orbit is:

The ratio of the radii of the first and second Bohr orbits is:

The Lyman series is obtained when electrons jump to:

The energy of the electron in the nth orbit of hydrogen is proportional to:

Rutherford's model could not explain:

Large angle scattering of alpha particles occurs for:

Why is a thin gold foil used in the alpha scattering experiment? (2 marks)

What is the distance of closest approach? Write its expression. (2 marks)

Why are hydrogen spectral lines sharp and discrete? (2 marks)

Write the Rydberg formula for the wavelengths of the hydrogen spectrum. (2 marks)

What happens to the speed of an electron as it moves to higher Bohr orbits? (2 marks)

Distinguish between emission and absorption spectra. (2 marks)

Why is the energy of a bound electron negative? (2 marks)

Name the series of hydrogen spectrum that lies in the infrared region. (2 marks)

What is the significance of the negative total energy of an electron in an orbit? (2 marks)

State the condition for an electron orbit in terms of de Broglie wavelength. (2 marks)

Calculate the energy and wavelength of the photon emitted when an electron in hydrogen jumps from n = 4 to n = 2 (hc = 1240 eV nm). (3 marks)

Find the radius of the third Bohr orbit of hydrogen and the ratio of its radius to that of the first orbit. (3 marks)

For an electron in the n = 3 orbit of hydrogen, find its kinetic energy, potential energy and total energy in eV. (3 marks)

Calculate the longest and shortest wavelengths of the Balmer series (R = 1.097 x 10^7 m^-1). (3 marks)

The speed of the electron in the ground state of hydrogen is 2.18 x 10^6 m/s. Calculate its de Broglie wavelength (h = 6.63 x 10^-34 J s, m = 9.1 x 10^-31 kg) and compare it with the circumference of the first orbit. (3 marks)

Read the passage and answer the questions. In 1911, Geiger and Marsden directed a beam of 5.5 MeV alpha particles from a radioactive source at a gold foil about 2.1 x 10^-7 m thick. A rotating detector counted scintillations at different angles. About 1 in 8,000 particles was deflected by more than 90 degrees. (i) What does the rare large-angle deflection indicate? (ii) Why was a vacuum chamber used? (iii) What model of the atom did Rutherford propose? (5 marks)

Read the passage and answer the questions. When an electric discharge is passed through hydrogen gas in a tube, it glows and its light, seen through a spectrometer, shows sharp red, blue-green and violet lines. (i) Which series do these lines belong to? (ii) Which transition gives the red line? (iii) Why is the spectrum not continuous? (5 marks)

Read the passage and answer the questions. Astronomers observe dark lines at the Balmer wavelengths in the spectrum of a star, showing that cooler hydrogen gas surrounds it. (i) What type of spectrum is this? (ii) Why do the dark lines appear at the same wavelengths as the emission lines? (iii) Which energy level must the absorbing atoms be in? (5 marks)

Read the passage and answer the questions. Bohr's postulate that angular momentum is quantised seemed arbitrary in 1913. In 1924, de Broglie suggested that electrons have wave nature. (i) State de Broglie's relation. (ii) Show how it leads to mvr = nh/(2 pi). (iii) What does n represent in terms of waves? (5 marks)

Read the passage and answer the questions. A beam of electrons of energy 12.1 eV passes through hydrogen gas at room temperature, and the gas emits light. (i) Up to which level can the hydrogen atoms be excited? (ii) How many spectral lines are emitted? (iii) Name the series of each line. (5 marks)

Describe the Geiger-Marsden alpha scattering experiment with a labelled diagram. State the observations and conclusions, and draw the graph of number of scattered particles against scattering angle. (6 marks)

State Bohr's postulates and derive expressions for the radius and the total energy of the electron in the nth orbit of a hydrogen atom. (6 marks)

Draw the energy level diagram of hydrogen and explain the origin of the Lyman, Balmer, Paschen, Brackett and Pfund series, with their spectral regions. (6 marks)

Explain the limitations of Rutherford's model and how Bohr's model overcame them. State two limitations of Bohr's model. (6 marks)

Explain de Broglie's explanation of Bohr's quantisation condition with a diagram of standing waves in an orbit. (6 marks)