The CHEMICAL Basis of LIFE Chapter 4! The CHEMICAL Basis of LIFE

Life Requires About 25 Elements (4.1) Living things share the same building blocks Oxygen (O) Carbon (C) Hydrogen (H) Nitrogen (N)

Elements Matter Element Anything that takes up space and has mass Pure substance Can not be broken down any further by chemical means

Elements cont’ Trace Elements Eg: Elements < than .01% of your body Iodine (I) – lack causes thyroid problems Iron (Fe) – carries O2 Fig 4-1

Compounds Compounds Eg: Properties change Contains 2 or more elements in a fixed ratio Eg: Water, H2O Properties change H vs. O

Chemical Properties Are Based on the Structure of Atoms (4.2) Greek word atomos : “indivisible” Smallest piece of an element

Atoms cont’ – Subatomic particles (fig 4-4) Nucleus Protons and neutrons Most of atom’s mass Proton Positive charge An atom model Neutron Neutral charge Electron Negative charge No significant mass

Atoms cont’ “Electron Cloud” Video

Atoms cont’ Atomic Number Atomic Mass What can change? # of protons Does not change (eg: N has 7 protons, O has – 8 protons) What can change? Neutrons and e- can change Determines interactions / rxns Atomic Mass #P + #N

Isotopes Isotope Eg: What is changing?? Same # of protons, but different # of neutrons Eg: What is changing?? Carbon-12, Carbon-13 and Carbon-14 Fig 4-5

Isotopes cont’ Radioactive Isotope Nucleus “breaks down” Gives off radiation Can be used in organisms

Chemical bonds join atoms to one another (4.3) Rxns between atoms result in filled outer energy levels Atoms and e- get rearranged Chemical bond(s) form Two types… 2

Ionic Bonds Covalent Bonds Atoms transfer e- Atoms share e- Molecule Video Ionic Bonds Atoms transfer e- Eg: NaCl (table salt) more info… Covalent Bonds Video Atoms share e- Ex: H2 Molecule Any atoms held together w/ covalent bonds

Formulas Chemical formula Structural formula Space-filling model Eg: Fig 4-10 C6H12O6 Structural formula Space-filling model

Chemical Rxns Formation of new substance(s) Exothermic Endothermic rxn releases energy Endothermic rxn absorbs energy

Chemical Rxns cont’ 2 H2 + O2  2 H2O + energy Reactants Products Starting material (on left) Products Ending material (on right) Matter is rearranged Video Fig 4-11

Life depends on the unique properties of H2O (4.4) All living things depend on water Human cells are 70 to 90 % H2O

Structure of Water Hydrogen bonds Polar molecule Bond strengths: Ends have opposite charges Hydrogen bonds Hydrogen (weakly) attracted to ANY slight neg. Fig 4-12 Bond strengths: hydrogen < ionic < covalent

Water’s Life Supporting Properties Cohesion vs. Adhesion Cohesion molec. of same kind “stick” Adhesion unlike molec. “stick”

Life Supporting Properties cont’ Eg’s of Water’s Polar Properties Water being pulled through a plant Surface tension Fig 4-13

Life Supporting Properties cont’ Low Density of ice Water vs Ice density Usually solid is MORE dense than liquid Ice is LESS dense than water D = M/V WHY? Polarity and hydrogen bonding! Floating ice is important… Fig 4-15

Life Supporting Properties cont’ H2O’s ability to dissolve other substances Solution A uniform mixture of 2 or more substances Solvent Dissolves other substance, greater amnt. Solute Being dissolved, lesser amnt. Aqueous Solution water is the solvent, (aq) Video Fig 4-16 H2O dissolves ionic Ex: NaCl (salt, sodium chloride) Video H2O dissolves molecular Sugar (sucrose, C12H22O11)

Acids, Bases and pH pH Scale Describes how acidic or basic based on H+ ions Range 0 (acidic) to 14 (basic) 7 is neutral Fig 4-17

Acids, Bases and pH cont’ Cells are sensitive to pH changes Eg: Human Blood pH of 7.4 (slightly basic) Buffers Substance that helps soln. resist pH change

Permission Statement: Restricted to the use of New Berlin Eisenhower High School Students, Faculty and Staff. Contact the Science Department for usage permissions. ®2005, 2007 Video Citations: Holman, John (1996). Atlantis Soars Toward Mir. CNN Interactive. Retrieved on Oct 20th, 2005 from http://www.cnn.com/TECH/9609/16/shuttle.am/shuttle.launch.mov Mackenzie (2002). Sugar Dissolving. Charlotte County Day School. Retrieved on Oct 18th, 2005 from http://www.ccds.charlotte.nc.us/mackenzie/Chem/Dissolve%20NonElectrolyte/Dissolving_Sugar_Non-electrolyte.swf No Author (2005). NaCl Dissolving. Western Oregon University. Retrieved on Oct 18th, 2005 from http://www.wou.edu/las/physci/ch412/dis_nacl.mov No Author (2004). Jesus Lizard Running. I Blogger.com. Retrieved on Oct 24th, 2005 from http://helloshana.blogspot.com/ White, Brian (n.d.) Hydrogen Covalent Bonding. University of Massachusetts. Retrieved on Oct 20th, 2005 from http://intro.bio.umb.edu/111-112/111F98Lect/H2.mov

More on Ionic bonds “cation” “anion” Fig 4-8 Back to slide # 15…