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Chem Chemistry

ChemistryNEB 2076 (old course)

Why are alkali metals impart characteristic colours when introduced to the flame ? [2]

2

Answer

· Based on the official syllabus and past papers
Updated

Alkali metals impart characteristic colours to a flame due to the excitation and subsequent relaxation of their valence electrons.

When alkali metals (e.g., lithium, sodium, potassium) are introduced into a flame, the heat energy excites their outermost electrons to higher energy levels. These excited electrons are unstable and quickly return to their ground state, releasing excess energy in the form of visible light. The wavelength (and thus the colour) of the emitted light depends on the energy difference between the excited and ground states, which is unique for each alkali metal.

For example:

  • Lithium emits a crimson red flame.
  • Sodium emits a yellow flame.
  • Potassium emits a lilac flame.

This phenomenon is called flame emission spectroscopy and is used to identify alkali metals in qualitative analysis. The emitted colours are a result of the electron transitions specific to each element’s electronic configuration.

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