At my local college I've taken on a course about law and currently we are learning about contract laws and was curious about the binding nature of a contract. 

Let's say there is a stock broker and his client and they are both chatting on a social media site i.e. Facebook. If the stock broker demands a yearly payment and sends a contract to his client who never signed the contract but later decides to work together and if the stock broker does not do his job correctly and the client does not want to pay the broker. is the contract that was sent on Facebook but never signed legally binding?

I was wondering if because the document was sent through a non official medium if a the client is even bounded. 

I was also wondering if being silent about a contract implicate a concession to the contract?