Environmental Systems Chapter 2

Chemistry quick review Matter – mass + space Atoms – elements; periodic table; symbols Atomic number, mass number, isotope Radioactivity Radioactive decay, half-life Compounds – formulas Covalent bonds – molecules (very strong) Ionic bonds – ions (slightly less strong) Additional types of bonds Hydrogen bonds – polarity (fairly weak)

Water Strong covalent bonds hold oxygen and hydrogen together Oxygen is much more electronegative than hydrogen  it is an electron ‘hog’  the electrons spend more time around it than hydrogen  water is a polar molecule The slight – charge on the oxygen side of the molecule is attracted to the slight + charge on the hydrogen side of another molecule (hydrogen bonding) This polarity and hydrogen bonding of water causes all its other properties: Surface tension Capillary action Specific heat Density of ice Solubility

Important solutions Excess H+ ions in solution Acids Excess H+ ions in solution HNO3 (nitric acid) and H2SO4 (sulfuric acid) pH < 7 Bases Excess OH- ions in solution NaOH (sodium hydroxide) and Ca(OH)2 (calcium hydroxide) pH > 7

Matter The law of conservation of matter It’s a LAW! Chemical reactions must obey! How does this impact the environment? There is no ‘away’… Compounds Inorganic – no carbon or no carbon bound to hydrogen Organic – have carbon-carbon and carbon-hydrogen bonds Four important ones: Carbohydrates Proteins Lipids Nucleic acids (DNA & RNA)

Energy Energy - the ability to do work; power – the rate of work Forms of energy: Kinetic – energy of motion Potential – stored energy Temperature Kinetic energy of the molecules within a substance Energy has laws too! First law of thermodynamics Not created or destroyed, just changed Second law of thermodynamics Changes in energy result in a decrease in usable energy and an increase in entropy

Systems analysis Open system: exchanges of matter or energy Example – a lake: water flows in as well as out Closed system: no exchanges of matter or energy Example – not as common; some underground cave systems Which is Earth with respect to matter? How about energy? Steady state systems Input = output  system is not changing over time Most natural systems are in a steady state due to feedback Negative feedback loop – system returns to original state by decreasing its rate of change (resists) Positive feedback loop – system accelerates by increasing its rate of change (amplifies)