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Chemistry, GCSE, Research Study on ‘Francium and the alkali metals’

  1. Read the task in Box 1.
  2. Download each of the pdfs and read them. Keep these open so you can refer to them as you watch the video.
  3. Watch the video.

Step 1

The Task

Chemistry, GCSE, Research Study on ‘Francium and the alkali metals’, Oaklands School

Students studying triple science take one GCSE in each Biology, Chemistry and Physics. In Year 10, as part of their Chemistry coursework, they are given a research task worth 12% of their overall grade. This consists of five questions which students are expected to research independently using the Internet, the library and their own knowledge. The answers should be fully explained to GCSE level and written with correct spelling and grammar. The sources of included information should be cited and a full bibliography should be included.

This is the fifth and final question on the Research Study report:

"Scientists were able to explain the differences in reactivity of the alkali metals after the work of Neils Bohr on the structure of the atom. Describe the Bohr model of the atom. How can the Bohr model of atomic structure be used to explain the reactivity of alkali metals?"

In this task, it is important to explain abstract concepts clearly with the correct scientific vocabulary. Another important consideration is the choice of content; students need to provide enough relevant information to fully answer the question.

Step 2

Texts

Research Study on ‘Francium and the alkali metals’, Text 1

Niels Bohr proposed the Bohr model in 1913. Some people call it the Rutherford-Bohr model, as it was a modified version of the Rutherford model. The Bohr model is a planetary model consisting of negatively charged electrons orbiting a positively charged nucleus, much like our solar system, where planets orbit the sun but with electromagnetic forces causing attraction rather than gravity [9] Some main points of the Bohr model are that, electrons orbiting the nucleus have a set energy and size of orbit, the energy of the orbit depends on the size of the orbit, radiation is absorbed or emitted when an electron moves from one orbit to another [7].

The Bohr model of atomic structure can be used to explain the reactivity of alkali metals as it shows how many electrons need to be lost or gained by an atom, from the outer shell to create a full octet, all alkali metals only need to lose an electron. It also shows the distance, in shells, between the valence electron and the positively charged nucleus, giving us an idea of the electromagnetic force between the electrons and the nuclei. Examples of the Bohr model are shown below using the elements Lithium and Sodium.

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Research Study on ‘Francium and the alkali metals’, Text 2

The Bohr model has an atom of a small positively charged nucleus orbited by negatively charged electrons. [7] The Bohr model of atomic structure can be used to explain the reactivity of alkali metals because the atoms are stable with a full shell of electrons so the alkali metals only need to lose one electron to get a full shell. Their reactivity increases as you go down the group. As the electron is lost it gets further from the positive nucleus which is attracting it. This makes it easier for the outer electron to be lost. [8]

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Research Study on ‘Francium and the alkali metals’, Text 3

The Bohr model of the atom is named after the twentieth-century Danish scientist, Niels Bohr. The model says that an atom has a positively charged nucleus surrounded by electrons that have circular orbits around the nucleus. This model was inspired by the workings of the solar system and says that electrons are kept attracted to the nucleus by electrostatic forces rather than gravity. [9]

The Bohr model can explain the reactivity of the alkali metals because it says that atoms are at their most stable when they have a stable octet and seeing as the alkali metals only need to lose one electron to gain a stable octet they are very reactive.

The reactivity increases further down the group as the electron that needs to be lost is further away from the positively charged nucleus and so the electrostatic attraction between the electron and the nucleus is much weaker. The attraction is weakened as the elements further down the group have an increased atomic radius and so the shielding effect decreases the attraction between the outer electron and the nucleus.

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Step 3

Step 4

Download the transcript for this video.

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