Fig. 1 is a simplified energy-level diagram for a sodium atom in a flame test. A flame supplies energy to the atom. One outer electron can move to a higher ...
Question 1 Report
Fig. 1 is a simplified energy-level diagram for a sodium atom in a flame test. A flame supplies energy to the atom. One outer electron can move to a higher energy level, but this state is unstable. When the electron falls back, energy is released as yellow light. Students compare this effect with potassium compounds, which give a different flame colour because their electron energy levels are different. The same sample also contains sodium chloride dissolved in water.
(a) Describe what happens to the electron when it moves upwards in Fig. 1. [2]
(b) Explain why light is emitted when the electron returns to the lower level. [2]
(c) Use the idea of electron energy levels to explain why potassium gives a different flame colour from sodium. [3]
(d) What is the charge on a sodium ion in the sodium chloride solution? [3]
Answer Details
(a) [2] The electron absorbs or gains energy from the flame, then moves to a higher energy level.
(b) [2] The electron falls back to a lower energy level. The energy difference between the levels is released as light.
(c) [3] Potassium has different electron energy levels, so the gaps between its levels differ from those in sodium. Its electrons release a different amount of energy when they fall to lower levels. Therefore the light has a different wavelength and colour.
(d) [3] A sodium ion has charge +1. Sodium loses one electron, so it has one more proton than electrons.
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