Question 4
a. Locate the ‘Electrons in Atoms’ activity on DVD2 or the DVD online version available on
the website.
i. Using the Spectra tool for the hydrogen atom, click on the emission line with an
energy of just less than 1 eV and hence state the energy of this line in electron volts and to
two decimal places.
ii. Use the Energy levels tool to find the transition in the hydrogen atom which leads
to the spectral line you identified in part (i). State the initial energy level and the final energy
level of the transition.
b. Explain why the nitrogen ion N6+ is a hydrogen-like ion. Assuming the ion is for the major
stable isotope 14N, state which sub-atomic particles it contains and how many of each there
are in the N6+ ion. (Guideline: two or three sentences.)
c. Calculate the ground state energy of the N6+ ion (i.e. for n = 1), and the energy of the next
four highest energy levels (i.e. for n = 2, 3, 4, 5). Express your answers in eV and to an
appropriate number of significant figures.
d. Sketch an energy level diagram for a N6+ ion, labelling the energy levels with the values
you have calculated above. Be sure also to indicate the position and energy of the continuum
(Insert your sketch into your assignment document.)
e. What might cause the N6+ ion to make a transition between the n = 1 energy level and the n
= 2 energy level? Be as quantitative as you can in your answer.
f. A N6+ ion in its ground state absorbs an X-ray photon of energy 2.0000 keV. Explain what
happens to the ion and why. Be as quantitative as you can in your answer. (Guideline: up to
80 words in total.)

Question 5
In Book 7, Section 6.6 you learnt that late in its life, a star like the Sun can produce elements
as heavy as carbon through nuclear reactions in its core. However astronomers have found
stars that are between ten to a hundred times more massive than the Sun. While such massive
stars are very rare they are also very important since they are a source of elements heavier
than carbon and essential for life.

a. One such reaction fuses two nuclei of carbon-12 (
) to form an atom of neon (
with the emission of an ?-particle. Write an equation for this process, indicating the atomic
number and mass number of each of the products in the usual way.
b. Another reaction involving carbon-12 in stars is one in which a carbon-12 nucleus fuses
with a hydrogen nucleus (atomic mass of 1) to form a nucleus of nitrogen, releasing 1.95
MeV in the process.
Write down the equation for this process, and using values for the binding energy of the
hydrogen and carbon-12 nuclei of 0 MeV and –92.2 MeV respectively, calculate the binding
energy of the nitrogen nucleus. (Show all your working.)
c. Convert the energy liberated in the reaction in part (b) into the equivalent amount of energy
in joules, and then calculate the amount of mass that has been converted into energy as a
result of this process. Using SI units throughout show that the units for the mass are
kilograms. (Express your answers in scientific notation to an appropriate number of
significant figures.)
d. An alpha particle and an electron are 1.00 × 10-6 m apart from one another.
i. Assuming the values for charge and mass given in Table 3, calculate the strength of
both the electrical and gravitational forces between them.
ii. Given your results, briefly compare and contrast the nature of these forces in terms
of relative strength, dependence on separation distance and direction (attractive or repulsive).
Table 3. Charge and mass of an electron and alpha particle.
-1.6 × 10 C 9.1 × 10-31 kg
Alpha particle 3.2 × 10-19 C
6.6 × 10-27 kg
(Hint: You should review Coulomb’s Law and Newton’s law of gravity as discussed on pages
111 and 135 of Book 7 respectively and consider the form of the relevant equations and the
nature of the electric charges.)