Chrome has sophisticated memory management and each tab runs in its own memory sandbox. This makes it more secure, but at the cost of some memory efficiency.
Chrome basically pre-caches certain pages or links away from the current page in expectation of your clicking on the link. Instead of having to load everything from the web server, it can load most if not all from its ram cache of that page.
One thing you can do to reduce RAM usage (although it will make pages load slower) is to go in to chrome://settings, then advanced settings>privacy and uncheck-
Predict network actions to improve page load performance
You can also reduce RAM use is by uninstalling unnecessary plugins and extensions.