How do we know water is H2O if we can't see the atomic structure and how are the elements identified? Water has been shown to form when anything that contains two moles of hydrogen atoms combusted will happen to form 18 grams of water when combusted completely in an oxygen-rich environment. The first table of relative atomic mass (atomic weight) was published by John Dalton (1766–1844) in 1805, based on a system in which the relative atomic mass of hydrogen was defined as 1. Here’s the challenge: solids are relatively easily weighed, but under the right conditions, water, oxygen, carbon dioxide and hydrogen are all gases and not as easily weighed. In fact:Jöns Jacob Berzelius (1779–1848) was instrumental in the determination of relative atomic masses to ever-increasing accuracy.

Source: Forbes January 13, 2017 17:13 UTC