Basic Chemistry. Chapter 02

Transcription

1 1 Chapter 2 Vital Force - Vitality 1 Organisms composed primarily (96%) of only four elements Carbon, Oxygen, Hydrogen, Nitrogen COHN 2 Atomic Structure Atoms Smallest units of elements Consist of 3 subatomic particles Protons (+) Neutrons (no charge) Electrons (-) 3

2 2 Atomic Symbols Each element represented by unique atomic symbol Mass Number One or two letters Atomic Number First letter capitalized Atomic # Mass # Unit of measure is a Dalton 12 6 C Carbon Atomic Symbol 4 Isotopes: Isotopes Atoms of the same element with a differing numbers of neutrons Still has same # of protons 5 Radioisotopes Some isotopes spontaneously decay Unstable nucleus Radioactive decay transforms one element into another (i.e. Carbon-14 into Nitrogen-14) Give off energy in the form of rays and subatomic particles Dating Half life of C-14 (5.7k years) Can be used as tracers (Iodine*) Mutagenic Can cause cancer 6

3 3 Some Medical Uses for Low Level Radiation 7 Electrons In neutral atoms p = e- (+ balances -) Electrons are attracted to the positive nucleus Revolve around nucleus in orbitals Energy Levels (aka: electron shells) Bohr Model concentric circles around the nucleus 1 st Shell: 2 e- Subsequent Shells: 8 e- (Octet Rule) Goal = have full outer shell Reactive?? Why Hydrogen: 1 shell, goal = 2 e- All other atoms, goal = 8 e- How can an atom be neutral but unstable? So how do I become stable? Hmmmm 8 Bohr Models of Atoms 9

4 4 Organization of Periodic Table Elements grouped in periodic table based on characteristics Vertical columns = groups Horizontal rows = periods 10 Periodic Table (Revisited) Vertical columns indicate Practice!!! number of electrons in outermost shell Horizontal periods indicate total number of electron shells I 1 H Li Na K II III IV V VI VII 4 Be Mg Ca B Al Ga C Si Ge N P As O S Se F Cl Br VIII 2 He Ne Ar Kr Elements and Compounds Molecule vs. Compound Characteristics dramatically different from constituent elements (WHY?) 12

5 5 Formulas and Equations Chemical formula describes composition of a compound Ex: water = H 2 O (2 hydrogen atoms + 1 oxygen atom) Chemical Equations describes reaction between atoms and compounds Ex: combustion C 3 H 8 (propane) + 5O 2 3CO 2 + 4H 2 O + energy 13 Shape of molecules Are 3D, though look 1D on paper Final shape of molecule determines its biological role. Examples: enzymes, antibody/antigen recognition, hormones receptor cells recognize hormone insulin 14 Types of Bonds: Ionic Bonding What interacts? Ionic Bonds Octet rule: Atoms want 8 electrons in outer shell How to determine if an element will donate or accept? 15

6 6 Covalently Bonded Molecules -When atoms share electrons -Outer orbitals overlap -Strong and stable -Each atom has complete outer e- shell 16 Nonpolar Covalent Bonds Electrons are equally shared between atoms ex: Methane (CH 4 ) 17 Polar Covalent Bonds e - unequally shared between 2 atoms Why does this occur? Electronegativity Ex: water molecule (H 2 O) is polar Atoms assume slight change 18

7 7 Hydrogen Bonding (VIDEO) Weak Bond but 19 Properties of Water All of the following properties are caused by? High Heat Capacity High Heat of Vaporization Universal Solvent Cohesive & Adhesive High Surface Tension Less Dense in Frozen State 20 The Chemistry of Water: Heat Capacity Temperature/Heat/Kinetic Energy Water has a high heat capacity (specific heat) Specific Heat Definition: Water has a SH of 1 calorie Thermal inertia resistance to temperature change Slow change in temp (prevents rapid temp. fluctuations) What causes this?? 21

8 8 Heat of Vaporization (Evaporation) High heat of vaporization To raise water from ºC; ~1 calorie To raise water from 98 to 99 ºC; ~1 calorie However, large numbers of hydrogen bonds must be broken to evaporate/vaporize water To raise 1g water from 99 to ºC; ~540 calories! Uses: 1) Evaporative Cooling (sweating) % Humidity 2) Moderate coastal temperatures! 22 Solutions consist of: Solvent vs. Solute Water as a Solvent Ionic compounds dissociate in water 23 Polar compounds readily dissolve; hydrophilic Ex: Ammonia Nonpolar compounds do not dissolve; hydrophobic (fats, gasoline, oils) 24

9 9 Unusual Density Frozen water less dense than liquid water Max density = 4 C, below that will expand Sodas in freezer 25 Water Properties Continued Cohesive and Adhesive Cohesion water to water Adhesion water to polar surfaces High Surface Tension Caused by hydrogen bonds Who cares??? 26 Water as a Transport Medium 27

10 10 ph of Water: Acids Water Ionizes (draw out) ph of Water Acids dissociate in water to give H+ ion and an anion (Proton Donor) HCl Bases release OH- ions or take up hydrogen ions (H+) NaOH 28 Fig. 3-9 ph Scale 0 ph scale 1 Battery acid Measures concentrati on of H+ [H+][OH-] = Scale from 0 to 14 H + H + H + H + OH OH H + H + H + H + Acidic solution OH OH H + H+ OH OH OH H + H + H+ Neutral solution Neutral [H + ] = [OH ] Gastric juice, 2 lemon juice 3 Vinegar, beer, wine, cola 4 Tomato juice Black coffee 5 Rainwater 6 Urine Saliva 7 Pure water Human blood, tears 8 Seawater 9 10 Milk of magnesia OH OH OH H + OH OH OH H + OH Basic solution 11 Household ammonia 12 Household 13 bleach 14 Oven cleaner 29 ph Scale Logarithmic scale Each ph value represents 10X change in concentration of H + and OH - 30

11 11 The ph Scale 31 Buffers in Biology Help maintain ph (blood ph ~ 7.4) Donate protons when ph becomes too basic Accept protons when ph becomes too acidic Carbonic Acid/Bicarb in Blood 32