The Chemical Context of Life & Water & Life Chapter 2 & 3 Pages 28 - 55

Basic Chemistry Matter – anything that has mass and takes up space. Exists in three forms: Solid, Liquid or Gas.

Basic Chemistry All matter is composed of basic substances called Elements. Elements cannot be broken down to simpler elements (only into subatomic components).

Basic Chemistry Atom – unit of all matter – 114 different kinds, but only 25 are involved in life. C, O, H and N  96% of life. P, S, Ca and K  4% of life. Fig 2.1 Trace elements very specific places. Ex. Fe for blood and I (thyroid).

Basic Chemistry Neutrons and protons each weigh one Dalton (D) – electrons (1/2000 D). Nucleus  proton (+1), neutron (0) Each are 1 D. Orbital  electron (-1). Fig. 2.4 page 30

Basic Chemistry Atomic Number  number of protons & electrons. Ex. 8O, 1H, 6C Atomic Mass - weight of the protons and neutrons. Ex. 16O, 1H, 12C

Basic Chemistry Isotopes – atoms of the same element with a different mass (additional neutrons)  but have the same properties. Ex. 126C, 136C, 146C C-14 used in carbon dating.

Basic Chemistry Atomic model not accurate – golf ball nucleus has orbital of 1 km. Bohr’s Model

3-D Bohr’s Model

Basic Chemistry Orbital – particular volume of space that an electron is found most of the time. Electrons furthest away from the nucleus contain the most energy (reactive).

Basic Chemistry Atoms strive to complete their outer shells  stability. Ex Noble Gases (VIII) Reaction of Oxygen (O = O).

Basic Chemistry Only electrons come close enough to react. Different shells have electrons at varying potential energy – the more distant the e- the more energy it has (light causes chlorophyll e- to move to higher level).

Basic Chemistry Orbitals – first 2 shells most important biologically. 1s – one orbital  2 e- in circular orbits 2s – four orbitals  2 e- in circular orbits 2p – 6 e- in dumbbell shape pattern

Basic Chemistry Differentiating Terms: Compound – atoms of two or more different elements bond together. Molecule – smallest part of a compound that still has the properties of that compound.

Basic Chemistry The outer electrons – valence electrons, they are involved in bonding. Chemical Bonds: 1. Covalent – two or more atoms sharing outer shell electrons. a. Single bonds  share two electrons

Basic Chemistry b. Double bond  share four electrons c. Triple bond  share six electrons Electronegativity – attraction of one atom to another.

Basic Chemistry 2. Nonpolar Covalent Bond – equal electronegativity – sharing electrons equally. Nonpolar molecules will dissolve in other nonpolar solvents. Ex. Diatomic molecules and hydrocarbons. H2, O2, N2 and CH4

Basic Chemistry 3. Polar Covalent Bonds - unequal electronegativity – unequal sharing of electrons. The atoms with the most protons hoard the electrons  turning that side of the molecule negative. Ex. Water Polar molecules blend with other polar molecules.

Basic Chemistry 4. Hydrogen Bonds – weak bonds that are temporary. Usually involves an interaction between H and O or N.

Basic Chemistry Polar molecules with a magnetic attraction between the positive end of one molecule and the negative end of the other.

H bonds hold both sides of DNA

Basic Chemistry 5. Ionic Bonds – weak bonds caused by the transfer of e- from one atom to another, forming ions. Positive ions  Cations Negative ions  Anions Ionic Compounds are called salts.

Ionic Bonds

Basic Chemistry All chemical reactions – start with reactants and end with a product(s). 6CO2 + 6H2O  C6H12O6 + 6O2

Chemistry of Water Water constitutes 70 –90% of living tissue. Unique properties that determine some very important features of life. H bonds are constantly being formed and broken  liquid property. Four unique properties result from this.

Chemistry of Water 1. Cohesion – H bonds between H2O molecules. 1/20 the strength of covalent bonds but are able to hold the elements together.

Chemistry of Water Ex pulls water up stems – column holds together. Adhesion – water and other polar molecules binds water to walls – capillary action.

Chemistry of Water Ex Surface Tension – interface of air and water.

Chemistry of Water 2. Water Moderates Temperature – holds heat well. Takes one calorie to raise 1 g of H2O 1o C. Referred to 4.2 Joules Kilocalorie 1000 g of H2O.

Chemistry of Water a. Specific Heat – 1 cal/g/oC is high – so temperature change occurs slowly (Fe is 10X less). Hydrogen bonds absorb heat. Ex Stabilizes temperature of organisms and bodies of water. Ex Water absorbs the heat of metabolism.

Chemistry of Water b. Heat of Vaporation – takes large quantity of heat to vaporize water (steam). 540 cal/g of water Ex. Sweating results in great cooling (evaporative cooling). Ex Steam burns worse than water.

Chemistry of Water 3. Ice Floats – water is less dense as a solid than as a liquid. Above 4oC (39.2o F) water expands and contracts as it heats and cools. At 0oC (32oF) it is 10% less dense (four molecules maximum distance when frozen).

Chemistry of Water Ex Ice on the bottom of lakes would not melt all summer and would crush life on the bottom. Ex Ice on the top insulates from the much colder air above.

Chemistry of Water 4. Water as a solvent – solution has both solvent and solute – aqueous solution. Ex. Ionic compounds dissolve - cations  to negative O atoms and anions  positive H atoms. Ex. Polar covalent molecules are hydrophilic. Nonpolar covalent molecules are hydrophobic.

Chemistry of Water Dissociation of Water – slight separation H2O   H+ + OH- H+ (proton) – hydrogen ion OH- - hydroxide ion  becomes H3O in water. 1/554 million dissociations (10-7 M / ion).

Chemistry of Water Acid  increase in H+ or reduced OH-. Base  reduced H+ or increased OH- Neutral  equal parts H+ and OH-