The Chemical Basis of Life Chapter 2

Matter Substance that has mass and takes up space Compose all living things Generally found in 1 of 3 states Composed of 1 or more elements

Elements 92 occur naturally on Earth 4 make up 96% of the human body (CHON) Composed of atoms

Atoms Smallest particles that retains properties of an element Made up of subatomic particles: Protons (+) in nucleus Electrons (-) orbits nucleus Neutrons (no charge) in nucleus Protons and neutrons Mass of about 1 Electrons Mass is negligible (1/2000)

Reading A Periodic Table Elements differ depending on the number of subatomic particles Atomic symbol 1st letter or 2 (usually) Atomic number Determined by number of protons Element specific Mass number Determined by number of protons + neutrons

Isotopes Atoms with different number of neutrons Effects mass number how? Effects atomic number how? Can be stable or unstable (radioactive) Behave the same as respective element (electrons are key) Occur naturally as a mix in elements Living cells can’t distinguish between them Applications Dating fossils Biological tracers Brain scanning Cancer treatments Dangers Radioactive atoms give off energy that destroys chemical bonds when they collide

Chemical Properties of Atoms Electrons are key Move in orbitals called shells Repel one another, but attracted to protons Electron shells Outermost determines chemical properties Closer to the nucleus = lower energy and are filled first Holds up to 2 or 8 electrons Filled are unreactive Unfilled are reactive Number differs between atoms

Electron Shell Models HYDROGEN 1p+ , 1e- HELIUM 2p+ , 2e- CARBON OXYGEN 8p+ , 8e- SODIUM 11p+ , 11e- CHLORINE 17p+ , 17e- NEON 10p+ , 10e- electron proton neutron

Chemical Bonds Hold 2 or more atoms together Complete outer shells By sharing, donating, or receiving electrons Form molecules (H2, I2, and O2) or compounds (H20, NaCl, C6H12O6) Demonstrates emergent properties 2 H+ (gas) + O- (gas) = H2O (water) Na+ (metal) + Cl- (poisonous gas) = NaCl (table salt)

Ionic Bond One atom loses electrons  cation (charge?) Another atom gains these electrons  anion (charge?) Charge difference attracts the two Very weak bond Table salt (NaCl) cation anion

Covalent Bond Atoms share outer pair or pairs of valence electrons Single, double, or triple covalent bond Non-polar covalent Electrons shared equally E.g.: hydrogen gas/ H2/ H-H Polar covalent Electrons spend more time near most electronegative nucleus E.g.: water/ H20 electrons more attracted to O nucleus than to either H nuclei

Hydrogen Bond Positive charge on H attracts negative charge on another atom Individually weak, but often numerous = strong Important to many biological compounds E.g. water Makes up 70 – 90% of all living things Bonds create unique properties

Properties of Water Solubility Polarity Solvent: dissolving agent Solute: substance that is dissolved Solution: liquid mix of 2+ substances Aqueous solution when water is solvent Polarity ‘Like dissolves like’ Hydrophilic Sugar or salt and water Hydrophobic Oil and water

Properties of Water (cont.) Water movement Cohesion Creates surface tension Overfilling a glass, a ‘belly flop’, or beading of water Adhesion Water moves up plants against gravity or paper towels Temperature stabilization Molecule mov’t affects temp Hard to change H-bonds Increase  ice formation Reduce  evaporation Vary  internal temp.

0---------------------7-------------------14 pH Scale Measures [H+] of a solution (acidity) Change of 1 on scale means 10X change in [H+] (logarithmic scale) Highest H+ Lowest H+ 0---------------------7-------------------14 Acidic Neutral Basic

pH Scale (cont.) Acids Bases Neutrals Increase [H+] pH less than 7 Decrease [OH-] pH greater than 7 Neutrals Equal [H+] and [OH-] pH of 7.0

Buffer Systems Minimize shifts in pH Can accept H+ when in excess and donate H+ when depleted Form water Common in biological fluids Human blood at 7.4, slight deviations can be deadly

Making and Breaking Bonds Chemical reactions are often reversible Chemical equilibrium: forward and reverse reactions occurring at the same rate (no net change) Starting materials are reactants, ending are products # of atoms are conserved 1st law of thermodynamics Label the parts of this reaction