Topic 5.1: Structure of the Atom Questions

A charged conducting ball carries a charge of +6.4 × 10⁻¹⁹ C.

Determine how many electrons have been removed from the ball.

(e = 1.60 × 10⁻¹⁹ C.)

State what is meant by saying that electric charge is quantised.

An ion contains 17 protons, 20 neutrons and 18 electrons.

What is the correct nuclear notation for this nuclide?

Two nuclei are described as being isotopes of the same element.

Identify the quantity that must be the same for both nuclei, and the quantity that differs between them.

State why the energy of an electron in an atom can only take certain values rather than any value at all.

An alpha particle (charge +2e) is accelerated from rest through a potential difference of 1.5 × 10³ V between two parallel plates.

State, in electronvolts, the kinetic energy it gains.

An electron is accelerated from rest through a potential difference of 250 V.

(a) State, in electronvolts, the kinetic energy gained.

(b) Express this kinetic energy in joules.

Define the electronvolt.

A neutral atom of an element has nucleon number 39 and proton number 19.

State the number of protons, neutrons and electrons in this atom.

An atom has four energy levels.

The downward transitions and the energy each one releases are: P releases 1.0 × 10⁻¹⁸ J, Q releases 6.0 × 10⁻¹⁹ J, R releases 2.5 × 10⁻¹⁹ J and S releases 8.0 × 10⁻¹⁹ J.

Identify which transition emits the photon with the longest wavelength, and explain your choice.

A student claims that an atom of an element and a singly-charged positive ion of the same element 'are basically the same particle'.

Discuss this claim, identifying what stays the same and what changes between the neutral atom and its 1+ ion.

An iron nucleus has a binding energy per nucleon of 7.6 MeV and contains 60 nucleons.

(a) Calculate the total binding energy of the nucleus in MeV.

(b) Express this total binding energy in joules.

In the alpha-scattering experiment, a very small fraction of the alpha particles were repelled through angles greater than 90°, returning back towards the source.

Explain what this observation reveals about the size and charge of the nucleus.

Outline why the alpha-scattering experiment used a very thin metal foil and a source of fast alpha particles, rather than a thick foil or a beam of slow particles.

A magnesium ion is represented by the nuclide notation with nucleon number 25 and proton number 12, carrying an overall charge of 2+.

State the number of protons, neutrons and electrons in this ion, and explain why the electron count differs from a neutral magnesium atom.

A charged latex sphere is found to carry a charge of −1.12 × 10⁻¹⁸ C.

(a) Explain what is meant by saying that electric charge is quantised.

(b) Calculate the number of excess electrons on the sphere.

(c) State whether a charge of 2.4 × 10⁻¹⁹ C would be possible for a charged object, and justify your answer. (e = 1.60 × 10⁻¹⁹ C.)

Outline how Millikan's oil-drop experiment provided evidence that electric charge is quantised.

Electrons in a sample of atoms are excited to the fifth energy level (n = 5).

Determine the maximum number of different wavelengths that can appear in the emission spectrum as the electrons return to the ground state by every possible route.

A nuclear decay releases 4.3 MeV of energy.

(a) State what is meant by the unit MeV.

(b) Convert 4.3 MeV to joules, showing your working. (1 eV = 1.60 × 10⁻¹⁹ J.)

A bright line in a hydrogen emission spectrum has a wavelength of 434 nm.

Determine the size of the energy gap (in joules) between the two levels involved in this transition.

(h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹.)