Atoms & Isotopes (AQA GCSE Physics)

In 1909, Rutherford, Geiger and Marsden developed an experiment where alpha particles were scattered from gold foil.

Figure 1 shows the paths of some of the alpha particles that were fired at the gold foil during the experiment.

Figure 1

Explain how the paths of the alpha particles were used to develop the nuclear model of the atom.

In 1913, Niels Bohr improved upon Rutherford’s nuclear model by suggesting that electrons orbited the nucleus at particular distances.

Explain how the distance at which an electron orbits the nucleus can be changed.

Two isotopes of uranium are uranium-238 and uranium-235

The nuclear symbols for these are shown below.

What is meant by the term ‘isotope’?

How many protons are in the nucleus of a atom?

How many neutrons are in the nucleus of a  atom?

What is the mass number of a atom?

In the early 20th century, one model of the atom which was popular was the ‘plum pudding’ model, shown in Figure 2.

Figure 2

In 1909, Rutherford, Geiger and Marsden suggested a new model of the atom, called the ‘nuclear’ model, shown in Figure 3.

Figure 3

Describe the differences between the two models.

Rutherford’s experiment, as shown in Figure 4, was designed to test the plum pudding model.

It involved firing alpha particles at a thin sheet of gold foil, and then detecting which direction the alpha particles left the gold foil.

Figure 4

The plum pudding model predicted that alpha particles would pass straight through the atom with very few deflections, and even those would be small: no more than 4°.

The results of the experiment were that most of the alpha particles did go straight through, but some were deflected through large angles, and around 1 in 8000 was deflected straight back at the alpha source.

Why did this model lead to the plum pudding model being replaced by the nuclear model?

Figure 5 shows the paths of three of the alpha particles that were fired at the gold foil.

Figure 5

Use the nuclear model to explain the three paths, A, B, and C.

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:

State the number of protons number, the mass number and the number of neutrons in this isotope. 

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 .

Write down the symbols, using nuclide notation, for:

The deflection of α-particles by a thin metal foil is investigated with the arrangement shown in Figure 1.

The detector of α-particles, D, is moved around the path labelled WXY.

State the environment the apparatus must be enclosed in and explain why this is required for the experiment.

Explain the readings detected by D and the conclusions that were made about the nature of atoms at points W and X.

State what the readings detected by D at position Y conclude about the charge of the nucleus. Explain why.

A beam of α-particles produces a current of 3.5 pA.

Calculate the number of α-particles per second passing a point in the beam.

You will need to use the equations for current.

1 pA = 10⁻¹² A

The charge on a proton is 1.60 × 10^–19 C

Figure 1 represents a neutral atom of an isotope of element X.

Figure 1

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

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 .

Write down the symbols, using nuclear notation, for:

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

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

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

Explain what is meant by the term ‘neutral atom’. 

Refer to the number of electrons and protons.

is an example of nuclide notation for the element nitrogen.

Determine the number of neutrons in nitrogen.

Write the nuclide notation for another possible isotope of nitrogen.

Figure 1 shows the processes of excitation and ionisation.

Figure 1

Identify which of A and B is excitation and which is ionisation. Give a definition for each process.