The Nuclear Model of the Atom (Cambridge International IGCSE Physics): Exam Questions

State the term used to describe nuclides which have the same number of protons but different numbers of neutrons.

Table 1.1 describes four nuclides. The nuclide notation for lead-206 is missing.

Table 1.1

(i) State which two nuclides have the same number of protons.

(ii) Complete the table by filling in the nuclide notation for lead-206.

Extract:

| name of nuclide | radium-222 | radon-222 | lead-216 | lead-206 | | nuclide notation | Ra 88 222 | Rn 86 222 | Pb 82 216 | Pb 82 206 |

• Number of protons = bottom number
• Number of nucleons = top number
• Number of neutrons = nucleon number − atomic number A neutral atom is one with the same number of protons and electrons (so the overall charge is 0). The nuclide notation above does not show the number of electrons directly, but remember, that for a neutral atom this is just the same as the number of protons!

Using the information from Table 1.1

(i) State which two nuclides have the same number of nucleons.

(ii) State which two nuclides have the same number of neutrons.

(iii) State which one of the four nuclides has the most electrons orbiting when it is in a neutral atom.

Fig. 12.1 shows a diagram to represent a helium atom, and an incomplete key.

Complete the key in Fig. 12.1. State the name of each particle.

Extract:

Fig. 12.1 shows a diagram to represent a helium atom, and an incomplete key.

The table in Fig. 12.2 compares two isotopes of helium.

Fig 12.2

For each isotope, write the number of protons and the number of neutrons in the correct places in the table.

The nucleus of the helium atom in (a) is the same as an α-particle.

(i) Describe the penetrating ability of α-particles.

(ii) Explain why it is dangerous to swallow a source that emits α-particles.

Carbon-14 is a radioactive isotope of carbon. An atom of carbon-14 has 6 protons in its nucleus.

Another isotope of carbon is carbon-12.

(i) Determine the number of protons in a carbon-12 nucleus.

(ii) Determine the number of neutrons in a carbon-14 nucleus.

(iii) Determine the number of electrons orbiting the nucleus of a single carbon-14 atom.

Carbon-14 decays by emitting a β-particle.

State what happens to a nucleus of carbon-14 when it emits a β-particle.

People working with radioactive sources need to take safety precautions.

(i) A shielding material can absorb ionising radiation and reduce the damage to living tissue.

State a suitable material that will absorb all types of naturally occurring nuclear radiation.

(ii) Apart from using shielding, state how a person can reduce the amount of ionising radiation they absorb when they handle samples of radioactive substances.

Fig 1.1 show two different models of an atom.

Fig 1.1

The particles labelled X in the plum pudding model are also included in the model of the atom used today.

State the name of the particles labelled X.

Use words from the box to complete the sentences about the particles in an atom in today's model. Words can be used once, more than once or not at all.

The particle with a positive charge is ..........................................

The particle with the smallest mass is ..........................................

The particle with no charge is ..........................................

An electron is removed from the atom, as shown in Fig. 1.2.

Fig. 1.2

(i) State the name given to this type of atom.

(ii) State the effect on the charge of the overall atom.

Extended tier only

Fig. 1.1 shows the names of three different processes that take place in different locations.

Fig 1.1

Draw one line from each process to the location it takes place.

Extended tier only

This passage is about the differences between nuclear fission and fusion.

Tick the correct statements in the table below

Extended tier only

A nucleus of americium-241 has the nuclide notation shown.

${}_{95}^{241}\mathrm{ } A m$

(i) Determine the number of neutrons in a nucleus of americium-241.

number of neutrons = ........................................................ [1]

(ii) Determine the charge on a nucleus of americium-241.

charge = ........................................................ [2]

Americium-241 decays by emitting α-particles.

Put a tick in the box next to each correct statement.

square α-particles are electromagnetic waves.

square α-particles are fast-moving electrons.

square α-particles are helium nuclei.

square α-particles are stopped by a sheet of paper.

square α-particles can pass through 3 cm of aluminium.

Americium-241 has a half-life of 432 years. A sample contains 16 mg of americium-241.

Calculate the time it takes until only 4.0 mg of americium-241 are left in the sample.

time = .............................................. years

This notation represents the nucleus of a neutral atom of carbon-14.

C _ 6 ^ 14

State the number of:

(i) protons in the nucleus of an atom of carbon-14

(ii) electrons orbiting the nucleus of an atom of carbon-14

(iii) neutrons in the nucleus of an atom of carbon-14.

Extract:

Carbon-14 is an isotope of carbon. Carbon-12 is another isotope of carbon.

State the similarities and differences between the nucleus of carbon-14 with the nucleus of carbon-12:

• The two nuclei have the same;
• atomic number / proton number / number of protons;
• charge;
• The two nuclei have different:
• masses;
• nucleon numbers;
• numbers of neutrons;

The number of protons determines the element. All isotopes of carbon have 6 protons.

For isotopes, the only difference between the atoms is the number of neutrons.

The lower, smaller number is the atomic, or proton number:

• There are 6 protons; The higher, larger number is the mass, or nucleon number, with neutrons added to protons:
• There are (14 − 6) = 8 neutrons;

Carbon-14 is an isotope of carbon. Carbon-12 is another isotope of carbon.

Compare the nucleus of carbon-14 with the nucleus of carbon-12.

State the similarities and differences.

Scientists use carbon-14 to estimate the age of wood that is very old.

A very old sample of wood contains 1.0 × 10⁸ carbon-14 atoms.

When the sample was new, it contained 8.0 × 10⁸ carbon-14 atoms. The half-life of carbon-14 is 5700 years.

Estimate the age of the sample of wood.

age of wood = ........................... years

Use words from the box to complete the sentences about the charges in an atom. Words can be used once, more than once or not at all.

negative

neutral

positive

The charge on the nucleus of an atom is ..........................................

The charge on a proton is ..........................................

The charge on electrons orbiting the nucleus is ..........................................

A nucleus of radium-226 has the nuclide notation shown.

${}_{88}^{226}\mathrm{Ra}$

(i) Determine the number of protons in a nucleus of radium-226.

(ii) Determine the number of neutrons in a nucleus of radium-226.

(iii) Radium has another isotope, radium-223.

Write the nuclide notation for radium-223.

Radium-226 has a half-life of 1600 years.

A sample contains 8.0 mg of radium-226.

Calculate the time for the sample to decay until only 1.0 mg of radium-226 remains.

time = ............................................... years

A nuclear power station uses uranium to generate thermal energy.

The fuel for the power station is an isotope of uranium.

Explain the meaning of the term isotope.

When the nucleus of one particular isotope of uranium decays, it releases a β-particle. In the periodic table the entry for this isotope looks like this:

${}_{92}^{239}\mathrm{U}$

State the proton number, the mass number and the neutron number of this isotope.

A sample of rock includes some uranium-239.

The half-life of uranium-239 is 23 minutes.

Determine the fraction of the uranium-239 that remains after 46 minutes.

fraction remaining = ...........................................................

Extended tier only

The circles shown in Fig. 11.1 represent three gold nuclei. Three α-particles are approaching the gold nuclei.

On Fig. 11.1, complete the path of each α-particle.

The nuclide notation ${}_{Z}^{A}\mathrm{X}$ describes the nucleus of one type of atom.

On Fig. 11.1 draw a line from each symbol to the correct description for that symbol.

Two of the isotopes of hydrogen are hydrogen-2 * ( *${}_{1}^{2}\mathrm{H}$) and hydrogen-3 ( ${}_{1}^{3}\mathrm{H}$).

(i) State one similarity in the composition of their nuclei.

(ii) Describe how a nucleus of hydrogen-3 differs from a nucleus of hydrogen-2.

Extended Tier Only

In a nuclear fusion reactor, a nucleus of hydrogen-2 fuses with a nucleus of hydrogen-3 at an extremely high temperature. This fusion reaction produces an isotope of element X and releases a neutron.

(i) Explain why an extremely high temperature is needed when forcing these two nuclei together.

(ii) Using nuclide notation, complete the equation for this reaction.

${}_{1}^{2}\mathrm{H}$ + ${}_{1}^{3}\mathrm{H}$ ⟶

Fig. 11.1 represents all the particles in an atom which is a radioactive isotope of carbon.

Table 11.1 gives information about the particles shown in Fig. 11.1.

Using the information in Fig. 11.1, write in the empty boxes to complete

Table 11.1.

Extended tier only

Table 1.1 shows data about nine elements.

Table 1.1

Carbon-14 is a radioactive isotope with a nucleon number of 14. It decays by emitting β-particles.

Use data from Table 1.1 to write down the nuclide equation for this decay.

A radioactive sample is placed close to a detector. The radioactive isotope in the sample has a long half-life. The detector records a count rate of 597 counts/s.

Fig. 11.2 shows the readings when different materials are placed between the radioactive sample and the detector.

Fig. 11.2

Explain whether any α-particles, β-particles or γ-rays are emitted by the radioactive sample.

Fig. 10.1 represents a neutral atom of an isotope of element X.

State one similarity between this atom and a neutral atom of a different isotope of element X.

Extract:

Isotope X has 13 nucleons therefore, atomic number, A = 13 Isotope X has 5 protons, therefore, proton number, Z = 5 Hence, the nuclide notation is: ${}_5^{13}\mathrm{X}$ Recall the nuclide notation for a β-particle: ${}_-1^{0}\beta$ Consider the radioactive decay equation: ${}_5^{13}\mathrm{X}$ → ${}_-1^{0}\beta$ + ${}_?^{?}\mathrm{Y}$ Balance the atomic and proton numbers for both sides of the equation: Atomic numbers: 13 = 0 + ? Hence, atomic number for Y = 13 Proton numbers: 5 = −1 + ? 5 + 1 = ? Hence, proton number = 6 Obtain the nuclide notation for Y: ${}_6^{13}\mathrm{Y}$

The isotope of element X is radioactive. It decays to form an isotope of element Y by emitting a β-particle.

(i) Using Fig. 10.1 deduce the nuclide notation for the isotope of Y produced by this decay.

nuclide notation: $Y {}_\cdots^{\cdots}$ [3]

(ii) β-particles ionise the air they pass through less strongly than the same number of α-particles.

Suggest why this is so.

Extended tier only

When uranium-235 ($space_{92}^{235} \mathrm{U}$) is bombarded with a neutron, it forms an isotope of caesium (Cs) and an isotope of rubidium (Rb).

Complete the nuclide notation for this reaction.

U _ 92 ^ 235 + n _ square ^ square -> Cs _ square ^ 144 + Rb _ 37 ^ square + 2 n _ square ^ square

Extract:

When uranium-235 (U-235) is bombarded with a neutron, it forms an isotope of caesium (Cs) and an isotope of rubidium (Rb). The completed reaction equation is: U-235 + n → Cs-144 + Rb-90 + 2n. This is a nuclear fission reaction, where a neutron collides with an unstable nucleus, causing it to split into two smaller nuclei (daughter nuclei) and some neutrons.

Extended tier only

State and explain the process shown by the equation in (a).

Extract:

When uranium-235 (U-235) is bombarded with a neutron, it forms an isotope of caesium (Cs) and an isotope of rubidium (Rb). The completed nuclide notation for this reaction is: U-235 (subscript 92, superscript 235) + n (subscript 0, superscript 1) → Cs (subscript 55, superscript 144) + Rb (subscript 37, superscript 90) + 2 n (subscript 0, superscript 1)

The products of this fission reaction are caesium, rubidium and two neutrons. The neutrons move quickly away from the initial nuclear reaction. Therefore, energy from the nuclear store of the uranium nucleus is transferred into the kinetic energy store of the neutrons.

Extended tier only

(i) Describe and give a reason for the difference between the mass of the products and the reactants in the reaction from part (a).

(ii) State the energy transfer that takes place in the products of the reaction from part (a).

There are three naturally occurring isotopes of hydrogen: hydrogen-1, hydrogen-2 and hydrogen-3.

Hydrogen-1 is the simplest nuclide containing only one proton. Each isotope of hydrogen is represented by the symbol $H$.

Write down the symbols, using nuclide notation, for:

hydrogen-1 ...................................

hydrogen-2 ...................................

hydrogen-3 ...................................

Extract:

hydrogen-1: H₁¹ AND hydrogen-2: H₁² AND hydrogen-3: H₁³

Extended tier only

In a fusion reactor, a nucleus of hydrogen-2 and a nucleus of hydrogen-3 undergo fusion.

(i) State what is meant by nuclear fusion.

(ii) The fusion reaction produces a free neutron and one other particle.

Write down, using nuclide notation, the equation that represents this reaction.

Extended tier only

Fig 1.1 shows a neutron colliding with a nucleus of uranium-235, producing a number of products.

(i) Name the process shown in the diagram.

(ii) Complete, using nuclide notation, the equation that represents the reaction shown in Fig 1.1.

Extract:

Fig 1.1 shows a neutron colliding with a nucleus of uranium-235, producing a number of products.

The process shown in the diagram is: Nuclear fission.

The correct equation for this fission reaction is as follows: n^1_0 + U^235_92 → Ba^141_56 + Kr^92_36 + 3 n^1_0

(Where a neutron collides with uranium-235, producing barium-141, krypton-92, and 3 neutrons.)

Extended tier only

Explain how the process shown in Fig 1.1 can lead to a chain reaction.

Extract:

Fig 1.1 shows a neutron colliding with a nucleus of uranium-235, producing a number of products.

(i) The process shown in the diagram is:

• Nuclear fission; [1 mark]

(ii) The correct equation for this fission reaction is as follows:

n + U-235 → Ba-141 + Kr-92 + 3n

Example of calculation:

• Nucleon number: 1 + 235 = Ba + 92 + 3
• Therefore, Ba = (1 + 235) − (92 + 3) = 141
• Atomic number: 92 = 56 + Kr
• Therefore, Kr = 92 − 56 = 36

Extended tier only

This process releases energy.

Explain the energy transfer taking place in this reaction.