What is chemistry? What do you know about each of these? Atom Molecule Element Compound Biochemistry

Ch. 3 The Chemistry of Life You’re a big bag of chemicals!

Most of the human body is made up of water, H 2 O, 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)

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.

see also your testbook p.1064

compound 2 or more different elements chemically bonded Shown by chemical formula: H 2 O

molecule A group of atoms held together by covalent bonds. ex: C 6 H 12 O 6 Not all molecules are compounds. Ex: O 2

Chemical bonds valence electrons = Electrons in the outermost level of electron cloud.

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: H 2 O, O 2

Molecules with partial charges on opposite ends are polar molecules. Ex: H 2 O 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 CO 2, 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 CO 2 (nonpolar molecule)

Hydrogen Bonds Attraction between partial positive charge of hydrogen end (-) and partial negative charge of oxygen end (+).

Cohesion: the attraction between molecules of the same substance.

Adhesion - attraction between molecules of different substances.

DNA Hydrogen bonds hold DNA molecules together

Water Exists as solid, liquid, and gas on surface of Earth.

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. H 2 O + H 2 O  H 3 O + + 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 H 3 O + 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 H 3 O+ 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 H 3 O + Ranges from Lower numbers = more acidic Higher numbers = more basic Each point is 10x the H 3 O + ion concentration of the previous level.

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.