This is an excellent question as we would expect Mg to have a higher melting point due to its smaller ionic radius. One suggested reason that the melting point of Mg is lower than all the other group 2 metals is related to how the ions are structured in the lattice (known as crystal structure) when solid and liquid. It seems strange to consider arrangement of ions in a liquid but there is still some organisation of small groups of ions. For the other group 2 metals, it seems that their crystal structure is different in the solid and liquid state so additional energy is required to rearrange them. For magnesium, the crystal structure is the same in the solid and liquid state so no additional energy is required to reorganise the ions. Hence the lowest melting point. This is the best suggestion I could find but would be happy to hear if there are others...or if I am completely wrong! I will ask around.
Thank you!
Thank you.
You are very welcome!
why the melting point of Ca is higher than Mg？
This is an excellent question as we would expect Mg to have a higher melting point due to its smaller ionic radius. One suggested reason that the melting point of Mg is lower than all the other group 2 metals is related to how the ions are structured in the lattice (known as crystal structure) when solid and liquid. It seems strange to consider arrangement of ions in a liquid but there is still some organisation of small groups of ions. For the other group 2 metals, it seems that their crystal structure is different in the solid and liquid state so additional energy is required to rearrange them. For magnesium, the crystal structure is the same in the solid and liquid state so no additional energy is required to reorganise the ions. Hence the lowest melting point.
This is the best suggestion I could find but would be happy to hear if there are others...or if I am completely wrong! I will ask around.