<p> CHAPTER 2 – CHEMISTRY</p><p>2.1 MATTER</p><p>A. Anything that occupies space and has mass - mass – quantity of matter an object has - mass vs. weight</p><p>B. Elements - pure substances that cannot be broken down chemically into simpler kinds of matter - 90% of all living things contain C, H, O, N - chemical symbols</p><p>B. Atoms - simplest part of an element that retains all the properties of that element 1. nucleus – central core of atom with protons (+’ve charge) and neutrons (no charge) - atomic number = # of protons - atomic mass = # protons + # neutrons 2. electrons – travel in orbital outside of nucleus – each orbital has a different energy level; farther away from nucleus, more energy - first energy level holds a max of 2 electrons - next few, 8 - how many e- in outer orbital determines an atom’s reactivity</p><p>C. Compounds - elements do not usually exist by themselves - compound = two or more different elements chemically bonded to each other</p><p>- chemical formula – tells how many atoms of what element (H2O) - atoms are chemically stable when outermost energy level is filled - atoms tend to combine with each other to achieve stability - 2 kinds of bonds: 1. covalent - atoms share one or more pairs of electrons - polar covalent vs. nonpolar covalent</p><p>2. ionic - electrons are transferred from one atom to another; the resulting oppositely charged ions are attracted to each other</p><p>2.2 ENERGY</p><p>A. Energy and Matter - energy is the ability to do work or cause change - free energy is the energy in a system that is available for work - all atoms and molecules in a substance are in constant motion; rate of motion determines state (solid, liquid, gas)</p><p>B. Energy and Chemical Reactions - reactants – left side of equation; products – right side - chemical reactions that release energy = exergonic - chemical reactions that require energy = endergonic - both endergonic and exergonic chemical reactions require energy to start the reaction = activation energy - catalysts = chemicals that speed up reactions by lowering activation energy; reaction will then proceed spontaneously or with little energy input - enzymes = biological catalysts - redox reactions = involve transfer of electrons - oxidation reactions, atom loses one or more electrons; reduction reactions, atom gains one or more electrons</p><p>2.3 WATER AND SOLUTIONS</p><p>A. Polarity - Water is polar – even though it is NOT a charged molecule, the distribution of charges across the molecule is uneven - Water dissolves other polar substances (sugars, ionic compounds and some proteins) - Spheres of hydration B. Hydrogen Bonding - Force of attraction between a hydrogen atom with a slight positive charge and another atom or molecule with a partial or full negative charge; water “clings” to itself and other polar substances - Hydrogen bonding accounts for the unique properties of water - Cohesion and adhesion - Temperature moderation – water has a high heat capacity – it can absorb and release large amounts of heat with little temperature change - This allows organisms to keep cells at relatively stable temperatures despite changes in environmental temperature - High heat of vaporization – as liquid evaporates, the surface of the remaining liquid cools down – sweating - Water is densest at 4oC C. Describing solutions - a mixture in which one or more substances are uniformly distributed in another substance - no chemical alteration of either substance - solute vs. solvent - aqueous solutions (water is the solvent) are important to all living things D. Acids and Bases - breaking up of water molecule into two ions of opposite charge = dissociation</p><p>- H2O  H+ + OH-</p><p>- OH- = hydroxide ion; H3O+ = hydronium ion - Acids = # of hydronium ions > # hydroxide ions - Bases = # hydroxide ions > # hydronium ions (alkaline substances) - PH scale = measure of acidity or alkalinity (scale 0 – 14) - In living things, to maintain homeostasis, pH must be controlled - Buffers – chemicals which neutralize small amounts of acid or base added to a system</p>