Chemistry · Ch 4 — Hydrogen
Water
Water
Water (H₂O) is the single most abundant compound of hydrogen. The earth's surface is roughly 70% ocean, making the sea the major reservoir of water on the planet -- though sea water carries so many dissolved salts that it cannot be used directly for drinking or most other purposes. Water is essential to every living thing; the human body itself is about 65% water by mass.
Structurally, the water molecule is bent (V-shaped), with an oxygen atom bonded to two hydrogen atoms and an H-O-H bond angle of 104.5° -- close to, but a little less than, the ideal tetrahedral angle of 109.5°, the compression coming from the two lone pairs on oxygen exerting a stronger repulsion than the bonding pairs do. …
What this figure shows. A ball-and-stick model of a bent (V-shaped) water molecule: a large red oxygen sphere bonded to two smaller white/grey hydrogen spheres, with the H-O-H bond angle explicitly marked as 104.5°. …
Worked out. A "Do You Know?" box noting that water exists in interstellar clouds and the icy satellites of the solar system, where the ortho-to-para ratio (OPR) of water has recently drawn attention. Like molecular hydrogen, water can be classified by nuclear spin into ortho-H2O (the two hydrogen-nucleus spins parallel) and para-H2O (the two spins antiparallel), each sketched as a small bent O-H2 unit with the spin directions marked by arrows on the two H atoms. States that the OPR of H2 at 300 K on Earth is 3:1, while the OPR of H2O at 50 K in interstella …