Dihydrogen monoxide (DHMO) What to do about the world’s most deadly compound… Dihydrogen monoxide (DHMO)

Unit 2 – Bio-molecules and Biochemistry The Chemistry of Life

It all starts with Water Life depends on water! Why do you think water is so special? Water’s formula is H2O, two hydrogens covalently bonded to one oxygen.

Water’s Shape Water is a polar molecule, meaning a covalent bond that doesn’t share electrons equally Oxygen is slightly negative (bc it hogs the electrons) The Hydrogens are slightly positive (bc they miss out on the electrons) Since positive and negative charges attract, this creates a weak bond called a hydrogen bond.

COHESION Thanks to the polarity and hydrogen bonds… Water molecules stick to other water molecules. This is called Cohesion. (Co – think couple) Ex: Surface Tension – enables organisms to walk on the water

ADHESION Thanks to the polarity and hydrogen bonds Water molecules stick to other (non-water) surfaces. This is called Adhesion (think adhesive, like glue) Ex: Adhesion works with cohesion to provide capillary action in plants and allows them to move water from roots to leaves

High Specific Heat Thanks to polarity and the H bonds, water resists changing temperature This is good because 3/4ths of Earth is covered in water. That water absorbs or releases heat to regulate the local weather. Creates very stable marine and coastal environments Prevents extreme temperature fluctuations

Evaporative Cooling The high specific heat is also good for animals. As water evaporates, it removes heat from a surface This is how sweating keeps you cool!

Density of Water Water doesn’t follow the normal rule of density. MOST solids sink because they are very dense, but solid water (ice) floats because it is actually less dense. Water becomes more and more dense until 4*C After 4*C, it changes and becomes less dense as the molecules “spread out” and freeze. This is good for life because floating ice prevents lakes and streams from freezing solid.

Density of Water (Gas)

Density of Water (Liquid)

Density of Water (ICE)

Water – the Universal Solvent The polarity of water helps it dissolve just about anything which makes it important for the chemistry of living things Hydrophilic – “water loving”, substances that dissolve easily in water (i.e. salt) Hydrophobic – “water fearing”, substances that will not dissolve in water, these are non-polar compounds (i.e. oil)