Alkali and alkaline earth metals impart colours when heated over the burner, it is due to?
Correct answer: C. De-excitation of electrons from higher energy levels to lower energy levels
- A. Smaller electronegativity of alkali metals
- B. The smaller ionic radius of these metals
- C. De-excitation of electrons from higher energy levels to lower energy levels
- D. Excitation of electrons from low energy levels to higher energy levels
Explanation
Alkali metals have low ionization energies. The energy from the flame is sufficient to excite electrons to a higher energy level. The excited state is unstable hence, electrons emit energy and come back to their original levels. These energies fall in the visible light region hence the burner has color as excited electrons lose energy and become de-excited.
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About Reactions of Group I Elements
Group I elements have one valence electron, so their reactivity increases down the group as ionisation energy decreases. Their reactions with water, oxygen, hydrogen and halogens produce hydroxides, oxides, hydrides and halides, while the behaviour of lithium differs from the heavier metals because of its small ionic size.
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