What is chemistry?
What do you know about each of these?• Atom• Molecule• Element• Compound• Biochemistry
Biochemistry
Ch. 3 The Chemistry of Life
You’re a big bag of chemicals!
• Most of the human body is made up of water, H2O, with cells consisting of 65-90% water by weight.
• Most of a human body's mass is oxygen. Carbon, the basic unit for organic molecules, comes in second.
• 99% of the mass of the human body is made up of just six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
atom
• Basic unit of matter.
• Made up of protons, neutrons, and electrons
(100 million atoms = pinkie width)
http://www.csmate.colostate.edu/cltw/cohortpages/viney/atom.jpg
proton
• Small particle in nucleus (center) of atom.
• Positively charged.
• Number of protons = atomic number.
• Very small but important mass.
neutron
• same mass as protons.
• in nucleus with protons.
• no charge = Neutral
• held together with protons by strong forces.
electron
• Negatively charged particle.
• Attracted to positively charged nucleus.
• Constantly in motion in electron cloud outside nucleus.
• Very small mass (1/1840 mass of proton).
• # of electrons = # of protons, so atoms are neutral in charge.
element
• Pure substance made of atoms with same # of protons.
• > 100 known.
• Represented by one or two letter symbols: C, O, Ca, Fe
• Organized in Periodic Table of Elements.
http://www.corrosionsource.com/handbook/periodic/periodic_table.gif see also your testbook p.1064
compound
• 2 or more different elements chemically bonded
• Shown by chemical formula: H2O
molecule
• A group of atoms held together by covalent bonds.
ex: C6H12O6
• Not all molecules are compounds.
Ex: O2
Chemical bonds
valence electrons = Electrons in the outermost level of electron cloud.
http://members.tripod.com/craigjm/Atom2-2.jpg
chemical bonds
2 types: Ionic and Covalent
• Ionic bonds - electrons are moved from one atom to another to form ions (charged atoms).
• Oppositely charged ions are attracted to each other. Ex: Na+ and Cl- are ions.
• Covalent bonds - electrons are shared between atoms.
• Molecule - atoms joined by covalent bonds. Can be the same or different elements Ex: H2O , O2
• Molecules with partial charges on opposite ends are polar molecules. Ex: H2O
More protons in oxygen nucleus attract shared electrons to O end of molecule.
• Oxygen end of molecule = slightly negative.• Hydrogen end = slightly positive.
polarity
Water is a polar molecule!
• Other molecules, like CO2, are nonpolar.
Their electrons are distributed evenly, so they have no charge.
• Polar molecules do not “like” nonpolar molecules; they will not mix because they have no attractive charges.
Carbon dioxide CO2 (nonpolar molecule)
Hydrogen BondsAttraction between partial positive charge of hydrogen end (-)
and partial negative charge of oxygen end (+).
http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/graphics/water.gif
Cohesion: the attraction between molecules of the same substance.
http://wwwchem.csustan.edu/chem2000/Exp5/bulk_h2o.gif
Adhesion - attraction between molecules of different substances.
http://www.dnareplication.info/images/dnadoublehelix2.jpg
DNA
Hydrogen bonds holdDNA molecules together
Water
• Exists as solid, liquid, and gas on surface of Earth.
http://food.oregonstate.edu/images/learni/w20.jpg
Ice Floats
• When water freezes, hydrogen bonds lock the molecules in place with spaces between them.
• Ice is less dense than water, so rivers and lakes don’t freeze solid.
Why is this important to living things?
Water absorbs and retains heat
• H-bonds always breaking and forming so…
• Water absorbs lots of heat and takes a long time to cool.
• Large bodies of water moderate the temp. of earth
Mixture - material composed of two or more elements or compounds that are PHYSICALLY MIXED, NOT chemically combined.
Ex: salt and pepper, gases in atmosphere.
solutions
• Mixtures of liquids.
• When something dissolves in water, the water molecules surround the ions of the substance.
• The water is the solvent.• The dissolved substance is the solute.
Water molecules can react to form ions.
H2O + H2O H3O+ + OH-
(water hydronium ion + hydroxide ion)
(In pure water, only 1 out of 550 million molecules forms ions.)
acids
acid = compound that forms extra hydronium ions when dissolved in water.
Acidic solution have higher concentration of H3O+ ions than pure water and pH below 7.Ex: vinegar, lemon juice
bases
base = compound that gives hydroxide ions in solution.
Basic solutions have lower concentrations of H3O+ than pure water and have pH higher than 7.
Ex: bleach, lye, ammonia
pH scale• “Potential of hydrogen”• Measure of how acidic or basic a solution is
• Shows concentration of H3O+
• Ranges from 0 - 14• Lower numbers = more acidic• Higher numbers = more basic
• Each point is 10x the H3O+ ion concentration of the previous level.
http://www.guardiantrader.com/images/ph_scale.gif
Buffers
• Substance that reacts to prevent sharp, sudden changes in pH.
Ex: baking soda
• Oxygen (65%) • Carbon (18%) • Hydrogen (10%) • Nitrogen (3%) • Calcium (1.5%) • Phosphorus (1.0%) • Potassium (0.35%) • Sulfur (0.25%) • Sodium (0.15%) • Magnesium (0.05%) • Copper, Zinc, Selenium, Molybdenum, Fluorine, Chlorine,
Iodine, Manganese, Cobalt, Iron (0.70%) • Lithium, Strontium, Aluminum, Silicon, Lead, Vanadium,
Arsenic, Bromine (trace amounts) • Reference: H. A. Harper, V. W. Rodwell, P. A. Mayes, Review of
Physiological Chemistry, 16th ed., Lange Medical Publications, Los Altos, California 1977.
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