what is the difference between ram 1rx16 vs 1rx8?
The difference is the memory density. 1Rx16 is lower density memory than 1Rx8. 1Rx16 memory is very hard to find, and since the 8 GB chip is 1Rx8 and you want to add another one, that is what you should look for. Here is the crucial memory report which has compatible memory for your notebook.