Question

Beryllium and magnesium do not give color to flame whereas other alkaline earth metals do so. Why?

Answer 1

Hint: If any substance shows color when heated means the substance has loosely bound electrons. If the substance has loosely bound electrons they will get excited to higher energy while heating and come back to ground state after releasing some energy. That energy we can see in the form of color.

Complete step by step answer:
* We know that group IIA elements are called alkaline earth metals.
* When alkaline earth metals are heated the electrons are excited to higher energy levels and when they drop back to the ground state, energy is emitted in the form of visible light. Then we can see the color. 
* But in case of beryllium and magnesium the concept is different.
* Beryllium and magnesium are small in size, due to this the effective nuclear charge will be high, meaning their nucleus binds the electrons very strongly.
* Therefore they require a high amount of energy to excite the electrons and are not excited by bunsen flame.
* Hence, beryllium and magnesium elements do not exhibit any color to flame.
* The electrons in beryllium and magnesium are too strongly bound to get excited by flame. Hence, these elements do not impart any color.

Note: Don’t be confused with the alkaline earth elements. Beryllium and magnesium also belong to alkaline earth elements. Due to their small size it shows high nuclear effective energy. Due to this they beryllium and magnesium do not give color to flame.