# Melting point of alkaline earth metal carbonates

The melting point of carbonates of group 2 elements is (From Wikipedia)

• $\ce{BeCO3}$ : 54
• $\ce{MgCO3}$ : 540
• $\ce{CaCO3}$ : 1339
• $\ce{SrCO3}$ : 1494
• $\ce{BaCO3}$ : 811

A similar trend is followed by alkali metal carbonates (from Wikipedia). But in the inorganic chemistry book by Shriver and Atkins, this is given

Is there a difference between decomposition temperature and melting point? Or is the values given in the book wrong?

Melting and decomposition are different things, as you guessed in your question.

Melting:

Something can melt, and then re-solidify, undergoing a physical but not chemical change.

A simple example would be ice, but it is also true for many chemicals. For example tert-butanol is a solid at room temperature (at least in a well air-conditioned lab), but melts readily at slightly elevated temperatures without any degradation. Dimethylsulfoxide is another example of a chemical which often solidifies in a cool lab, but can be melted back down with only the heat of your hand.

Decomposition:

Decomposition is a different thing, whereby the material undergoes a chemical change (usually in addition to physical change). This is often seen in laboratory settings when trying to measure the melting point of molecules with high melting points, such that at the temperatures needed to melt the solid, side reactions are often observed, destroying the material. For this reason, in the literature, you will see melting points reported as mp. (decomp.), i.e. the temperature at which your molecule decomposed rather than melted.

• So barium carbonate melts before decomposing? – Aditya Dev Dec 13 '15 at 17:04
• The data you present certainly suggests so, which is entirely possible. You could try looking up the sources cited by Wikipedia and Atkins' to find the conditions used to measure the melting and decomposition points, as you can only really compare values if they were measured under the same conditions (for instance, if they were both measured by heating in the open atmosphere, or under inert atmosphere, or under vacuum and extrapolated back to melting/decomposition values at atmospheric pressure). – NotEvans. Dec 13 '15 at 17:07