What six elements are most important to human life?
You just need to remember... CHNOPS + Ca
Carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur and calcium. Phosphorus actually belongs at #7 on the list.
Many books list the top six as CHNOPS, but there is actually more Ca than P (1.5% to 1%), but it is hard to make as good of a mnemonic using Ca rather than P I guess... ;-)
These seven elements that make up the majority of our bodies, approximately 98% of our mass!
I highly recommend checking out the NOVA documentary "Hunting the Elements " which is also easily found on YouTube. When you find the full video, skip ahead to 58:00 minutes for the part of the video that discusses the elements of life, or... CHNOPS. The video is informative and funny!! It is worth watching the full video if you feel like geeking out for about 2 hours.
Here is a review of basic of organic chemistry for biology students.
Hope this helps!