Thank you for writing to Jewish Values Online.
I take it that you wish an answer to your question using a quite literal reading of the text. That is not my usual approach, but I will try to do so in my answer.
As you may recall, the Tanakh (Hebrew Scriptures, or Jewish Bible) in Shemot (Exodus) describes in full detail how the ten sayings (not actually ten commandments, as the first two are not things one may undertake directly) were inscibed on the two tablets, five and five. This was true both for the first set of tablets which Moses smashed on seeing the people engaged in the tragic 'sin' of the golden calf, and for the second set of tablets which Moses carved and brought back to the people. So yes, the text tells us clearly that there were two sets, each of two tablets, each tablet having five statements carved or etched on it.
As for why, in the first instance it is what G-d did. What right have I (or anyone) to question G-d's motives? Yet, the rabbis did just that, seeking an explanation in the text of the sayings themselves. What they found was that the sayings divide nicely into the positive and negative instructions, with five positive instructions on the first tablet, and five negative instructions on the second. We may speculate that this is the reason that G-d used two tablets, rather than one - but we will never really know.
I hope that this response is helpful in some way.
I have to point out that yours is not a question or topic that focuses on Jewish values, mores, ethics, or proper behavior, and so is not really suited to the purpose of this web site. There are many other Jewish resources and web sites that answer more general questions; for this type of information I suggest that you seek them out. Please return here to ask your questions about Jewish values, moral and ethical issues, and proper behavior.
Answered by: Rabbi Joseph Blair