So, let’s start from the very beginning.
“In the beginning, there was nothing. Then suddenly there was something.”
Okay, the Big Bang is probably a little bit too far back. Let’s just go back to the fundamentals of chemistry for now, yeah?
One of the big things in chemistry, that makes our lives (and calculations and related problems) soooooo much easier is… *drumroll please*… the ever wonderful, the amazing, the always-provided-in-tests PERIODIC TABLE. This is where we will start.
Way back in the day, when elements were being discovered left, right and centre, scientists were playing around with the elements, like they were playing solitaire with a pack of cards. One very bright spark, by the name of Dimitri Ivanovich Mendeleev, developed the Periodic Table that we know so well today. The elements were listed horizontally by their 
atomic weight and when chemical characteristics began to repeat, a new row was started. Mendeleev’s Periodic Table even predicted the existence of elements that hadn’t been discovered yet!
These are two websites that have “interactive” periodic tables. More information is provided for each element (if so desired).
In terms of chemistry, the best part of the periodic table is that it displays the chemical symbols for the elements (e.g. Na for sodium, W for tungsten) and the atomic weight (e.g. S – 32.07gmol-1 or C – 12.01gmol-1).
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