Hydrogen H Atomic Number: 1 Atomic Weight: 1.008 _______________________________________________________________________________ Human Physiology: - Building block of life - Simplest element - Part of H²O (water) which is essential to life and present in all organics Prevalence: - Most plentiful gas in universe - Makes up 98% of known universe Sources: - Water abundant throughout universe - Heavy water is toxic Deficiency: - As part of water can cause dehydration Excess: - In theory could asphyxiate by denying 0² - Not toxic but highly flammable and explosive