Q.What are the characteristic colours imparted by the II A elements?

When heated in a flame, the outer electrons of Ca, Sr and Ba are excited and emit visible light of characteristic colours on returning to the ground state; Be and Mg do not show this because their electrons need too much energy to be excited by an ordinary flame.

When a compound of an alkaline earth metal (Group IIA) is heated in a Bunsen flame, the thermal energy of the flame excites the outer (valence) electrons of the metal atom to higher energy levels. Since this excited state is unstable, the electron falls back to its original (ground) energy level, releasing the absorbed energy as light of a specific wavelength, which appears as a characteristic flame colour.

Characteristic flame colours of Group IIA elements:

• Beryllium (Be): no characteristic colour (its ionisation energy is too high; the flame is not energetic enough to excite its electrons)
• Magnesium (Mg): no characteristic colour, for the same reason
• Calcium (Ca): brick red
• Strontium (Sr): crimson red
• Barium (Ba): apple/pale green …