Why didn't my change come back to my wallet? And where is it now? I sent a payment for 198.52 mBTC using Electrum. There were two outputs. One for 196.39 mBTC that arrived. There was another output of 2 mBTC that I'm assuming  was processed as change. Does anyone know where the 2 mBTC might have gone? It didn't arrive with the recipient and it didn't come back to my wallet as change. 

I'm new to Bitcoin and I'm just concerned that in the future if I want to pay somebody, my payment may not reach them in full and, money during the transaction may disappear that I won't be able to recover. Both these things occured in this case and I'd like to understand why before I use Bitcoin for any more transactions.

Any help is greatly appreciated.
The change should be in your wallet. Open up Electrum and check if your balance is what you expect it to be. You can also look in the addresses tab and click the arrow next to "Change" to see your change addresses and the Bitcoin that is held there.

If you are just looking at an address in a block explorer, you will not see the change return to that address. This is because nearly all wallet software follow the recommendation of generating new change addresses for each transaction. It is important to remember that an address is not your wallet; your wallet contains several addresses, but an address itself is not your wallet. You should not be looking at a block explorer to determine your wallet balance; it will be inaccurate as the block explorer does not know what addresses are actually in your wallet.