The development of the model of the atom

Different radioactive isotopes emit different types of radiation.

One isotope of uranium (U) decays into thorium (Th) by emitting an alpha particle (He).

Which nuclear equation shows the decay of this isotope of uranium?

Tick () one box.

Figure 4 shows how the percentage of uranium atoms in a sample of one uranium isotope varies with time.

What is the time taken for 50% of the atoms of this uranium isotope to decay?

Use Figure 4.

What is the half-life of this uranium isotope?

Figure 5 shows how the percentage of uranium atoms varies with time for three different isotopes of uranium, A, B and C.

Figure 5

Which isotope is the most unstable?

Give a reason for your answer.

Tick () one box.

Figure 6 shows the nuclei of four different atoms.

Which nucleus in Figure 6 has the smallest mass number?

Tick () one box.

Which nucleus in Figure 6 has an atomic number of 4?

Tick () one box.

Which two nuclei in Figure 6 are isotopes of the same element?

Give a reason for your answer.

Scientists have replaced old models of the atom with newer models.

The nuclear model of the atom has a nucleus at the centre.

Which model of the atom was replaced by the nuclear model?

Tick () one box.

What does the nuclear model state about the mass of an atom?

Tick () one box.

Some atoms emit radiation.

Why do scientists sometimes change the model used to describe the structure of the atom?

Tick () one box.

When radioactivity was discovered, the dangers of radiation were not known.

Some scientists were irradiated and contaminated while working with the radioactive materials.

Describe the difference between irradiation and radioactive contamination.

Polonium-210 was one of the first radioactive elements to be discovered.

Polonium-210 (Po) decays into lead (Pb).

Complete the nuclear equation for polonium-210.

Polonium-210 has a half-life of 138 days.

A sample of polonium contains 256 000 atoms.

Calculate the time taken for the number of polonium-210 atoms to reach 16 000.

A sample of polonium contains equal numbers of polonium-209 atoms and polonium-210 atoms.

Polonium-209 has a half-life of 125 years.

Polonium-210 has a half-life of 138 days.

Explain how the activity of polonium-209 compares with the activity of polonium-210 in this sample.

Scientists developed different models of the atom as new discoveries were made.

Which particle in the atom was discovered first?

Tick (✓) one box.

In an experiment that led to the nuclear model of the atom, alpha particles were directed at a sheet of gold foil.

Figure 3 shows the path of three alpha particles passing close to a gold nucleus.

An alpha particle has a radius of 1.7 femtometres.

The radius of a gold nucleus is 4.2 times larger than the radius of an alpha particle.

Calculate the radius of a gold nucleus in femtometres.

Alpha particles are deflected by the gold nucleus.

What are the charges on an alpha particle and a gold nucleus?

Tick (✓) one box.

Which statement describes the force between the alpha particle and the gold nucleus?

Tick (✓) one box.

Which alpha particle in Figure 3 experiences the largest force from the gold nucleus?

Tick (✓) one box.

Table 1 lists different models of the atom in alphabetical order.

Which model in Table 1 was developed first?

Which model in Table 1 was developed last?

Scientists developed new models of the atom as new particles were discovered.

Draw one line from each particle to the year it was discovered.

The nucleus was discovered using an alpha particle scattering experiment. Alpha particles were directed at a sheet of gold foil. Figure 8 shows the paths taken by seven alpha particles, A, B, C, D, E, F and G.

Explain why alpha particle A takes the path shown in Figure 8.

Explain why the path of alpha particle B is more tightly curved than the path of alpha particle C.

What can be deduced about the atom from the paths taken by alpha particles D, E, F and G in Figure 8 ? Tick (✓) one box.

How is the Bohr model of the atom different from the nuclear model of the atom?

Explain how an electron can move up and down between energy levels in an atom.

The ancient Greeks thought that atoms were tiny spheres that could not be divided into anything smaller. Since then, different discoveries have led to the model of the atom changing. Some of the discoveries are given in Table 1.

Which discovery was the earliest?

Tick (✓) one box.

Which discovery was the most recent?

Tick (✓) one box.

The alpha particle scattering experiment led to the nuclear model of the atom. Figure 5 shows the paths of alpha particles travelling close to a gold nucleus.

Complete the sentences. Choose answers from the box. Each answer may be used once, more than once or not at all.

Alpha particles and gold nuclei are both positively charged. The gold nucleus the alpha particles.

As the alpha particle approaches the gold nucleus, the electric field strength experienced by the alpha particle.

As an alpha particle approaches the gold nucleus, the force experienced by the alpha

The results of the alpha particle scattering experiment were reproducible. What does reproducible mean?

Tick (✓) one box.