What is calcium oxide gas or solid?

Question

What is calcium oxide gas or solid?

Answer 1

The statement by kumorifox that gaseous CaO could not exist is not quite accurate, as evidenced by this article:

http://scitation.aip.org/getabs/servlet/...

It is true that at normal room temperature, in an inert atmosphere CaO is a solid and at elevated temperatures since CaO has a high melting point.

Calcium oxide can take up CO2 from the air and slowly reform calcium carbonate.  When calcium carbonate is heated above 800C CO2 is driven off and CaO is formed.  CaO boils (forming gaseous CaO) at around 2850C.  When CaO cools below 800C it begins to recombine with CO2 to form CaCO3 again.

Here is a misconception:  CaO boils at such a high temperature due to ionic bonds.  That's not quite true.  CaO melts and boils at such high temperatures because of the NETWORK of bonds formed in solid CaO.  You will notice that the MP and BP of CaO are very close, 2572 and 2850, indicating that once the network is broken apart there is very little in the way of bonding to keep it in the liquid state, and it vaporizes with little additional energy.  You get the same effect with networks of covalent bonds as in diamond and silicon dioxide.  It is the network arrangement of atoms that produces high melting points, not whether the internal bonds are ionic or covalent.

Answer 2

solid

Answer 3

CaO is an ionic compound, consisting of simple elemental ions. These are (almost) always solid.

Gaseous ionic compounds are not known, and ionic liquids have very bulky cations.