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substance consisting of 2 or more elements in a fixed ratio - has characteristics different from those of its elements
composed of individual atoms - cannot be broken down to other substances by chemical reactions
essential elements of life
25 - CHON make up 96% of living matter - most of remaining 4% are Ca, P, K, S, Na, Cl and Mg
result from electrical attractions between atoms that gain or lose valence electrons completely - strong bonds
form when atoms share a pair of valence electrons rather than gaining or losing - C, O, N and S readily form these - strong bonds
measure of an atom's attraction for the electrons it shared in a chemical bond with another atom
involve unequal electron sharing - O, N and S share unequally with H - not strong individually, but collectively strong - often critical for maintaing shape of many biological molecules
van der waals forces
weak forces that develop over very short distances between non polar molecules as moving electrons accumulate by chance in one part of a molecule or another - temporary zones of + or - charge make molecule polar - collectively, can stabilize a molecule- gecko
structure of molecules allow them to interact with other molecules - leads to emergent properties - support & maintain living systems
emergent properties of water
1. expansion upon freezing
2. ability to moderate temp
3. cohesion and surface tension
4. versatility as a solvent
moderation of temperature
water can absorb or release large amounts of heat with only a slight change in its own temperature
as a liquid evaporate, its remaining surface cools - helps stabilize temperatures in organisms and bodies of water
hydrogen bonds hold water molecules together - helps the transport of water against gravity in plants
a measure of how hard it is to break the surface of a liquid - related to cohesion - causes water to form droplets
water molecules are strong and slightly polar, so they ten to coat the surfaces of other polar and charged molecules and ion - reduce attraction between molecules or ions and promote their entry into a solution - prevents polar molecules or ions from reassociating - why water is called "the solvent of life"
substances that minimize changes in concentrations of H+ and OH- in a solution - consist of an acid/base pair that reversibly combines with H+
rain, snow or fog with a pH lower than 5.6 - cause by mixing of pollutants with water in the air - can damage life in lakes and streams - contributing to decline of some forests
acid in the oceans
CO₂ + H₂0 → H₂CO₃ (carbonic acid) - corrosive to shellfish and corals - causes "energy tax" where organisms spend more energy maintaining pH and less on reproduction
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