Unit 1 – The Chemistry of Life zChapter 2: Chemical Context of Life zChapter 3: Water and the Fitness of the Environment

Unifying Themes in Biology zEvolution~ biology’s core theme; differential reproductive success zEmergent Properties~ hierarchy of life zThe Cell~ all organism’s basic structure zHeritable Information~ DNA zStructure & Function~ form and function zEnvironmental Interaction~ organisms are open systems zRegulation~ feedback mechanisms zUnity & Diversity~ universal genetic code zScientific Inquiry~ observation; testing; repeatability zScience, Technology & Society~ functions of our world

Chemical Context of Life zMatter (space & mass) zElement vs. compound zThe atom zAtomic number (# of protons); mass number (protons + neutrons) zIsotopes (different # of neutrons); radioactive isotopes (nuclear decay) zEnergy (ability to do work); energy levels (electron states of potential energy)

Chemical Bonding zCovalent zDouble covalent zNonpolar covalent zPolar covalent zIonic zHydrogen zvan der Waals

Covalent Bonding zSharing pair of valence electrons zNumber of electrons required to complete an atom’s valence shell determines how many bonds will form zEx: Hydrogen & oxygen bonding in water; methane

Electron configurations of the first 18 elements.

Polar/nonpolar covalent bonds zElectronegativity attraction for electrons zNonpolar covalent electrons shared equally Ex: methane (CH 4 ) zPolar covalent one atom more electronegative than the other (charged) Ex: water (H 2 0)

Ionic bonding zHigh electronegativity difference strips valence electrons away from another atom zElectron transfer creates ions (charged atoms) zCation (positive ion); anion (negative ion) zEx: Salts (sodium chloride)

Hydrogen bonds zHydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom (oxygen or nitrogen)

van der Waals interactions zWeak interactions between molecules or parts of molecules that are brought about by localized change fluctuations zDue to the fact that electrons are constantly in motion and at any given instant, ever-changing “hot spots” of negative or positive charge may develop

Water zPolar~ opposite ends, opposite charges zCohesion~ H+ bonds holding molecules together zAdhesion~ H+ bonds holding molecules to another substance zSurface tension~ measurement of the difficulty to break or stretch the surface of a liquid zSpecific heat~ amount of heat absorbed or lost to change temperature by 1oC zHeat of vaporization~ quantity of heat required to convert 1g from liquid to gas states zDensity……….

Density zLess dense as solid than liquid zDue to hydrogen bonding zCrystalline lattice keeps molecules at a distance

Acid/Base & pH zDissociation of water into a hydrogen ion and a hydroxide ion zAcid: increases the hydrogen concentration of a solution zBase: reduces the hydrogen ion concentration of a solution zpH: “power of hydrogen” zBuffers: substances that minimize H+ and OH- concentrations (accepts or donates H+ ions)