Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Chemical Basis of Life

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ELEMENTS, ATOMS, AND MOLECULES Elements  substances that cannot be broken down by chemical means 92 naturally occurring elements – 25 are required by living organisms – 4 make up 96% of the human body  Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings COMPOUNDS & ATOMS Elements can combine to form compounds Compounds contain two or more elements in a fixed ratio * NaCl (Sodium Chloride) The smallest unit of an element is an atom

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATOMIC STRUCTURE Atoms consist of 3 subatomic particles: – Protons and neutrons occupy the central region (nucleus) of an atom A proton has a positive charge (+) A neutron is neutral, no charge – Electrons surround the nucleus An electron has a negative charge (-)

2 2 2 Protons Neutrons Electrons Helium atom Mass number = Protons Neutrons Electrons Carbon atom Mass number = 12 Electron cloud Nucleus 2e – 6e –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DIFFERENCES IN ELEMENTS – All atoms of a particular element have the same number of protons  atomic number – An atom's mass number (atomic mass) is the sum of its protons and neutrons Atomic Mass # C 6 11 # or protons

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Isotopes Atoms with different numbers of neutrons Same element

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ELECTRONS ARE ARRANGED IN ELECTRON SHELLS The chemical reactivity of an atom depends on the # of electrons in the outer shell – Atoms whose outer shells are not full share or transfer electrons to other atoms, forming molecules – 2 major types of chemical bonds Ionic bonds (lost or gained electrons) Covalent bonds (share electrons)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bell Ringer Describe one property of water, and give an example.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings POLAR MOLECULES A molecule share electrons equally is nonpolar A molecule share electrons unequally is polar – One part of the molecule is slightly positive, and one part is slightly negative – Water  Polar Molecule

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings HYDROGEN BONDS Attraction between slightly (+) regions and slightly (-) regions  hydrogen bonds Weak Bonds Hydrogen bond

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings WATER'S LIFE-SUPPORTING PROPERTIES Hydrogen bonds make liquid water cohesive Cohesion is the tendency of molecules to stick together Adhesion is the tendency of dissimilar particles or substances to adhere to each other. Surface tension results from the cohesion of water molecules  Measure of how difficult it is to stretch or break the surface of a liquid

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings WATER IS A UNIVERSAL SOLVENT A solution in which water is the solvent is an aqueous solution A solvent is the dissolver in a solution A solute is what is being dissolved When sugar (a solute) and water (a solvent) are mixed, a solution of sugar water results.

Ion in solution Salt crystal

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings WATER’S HYDROGEN BONDS MODERATE TEMP Water can absorb a large amount of energy without increasing in temperature  high specific heat Water also moderates temperature by evaporative cooling – The surface cools as the hottest molecules leave  vaporize

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ICE IS LESS DENSE THAN LIQUID WATER Hydrogen bonds in ice create a stable, 3 - dimensional structure Fewer molecules in the same volume Ice Hydrogen bonds are stable Liquid water Hydrogen bonds constantly break and re-form Hydrogen bond

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bell Ringer Why is water a polar molecule? Draw a water molecule, and label the following: oxygen, hydrogen, covalent bond, positive, negative

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings BASIC AND ACIDIC CONDITIONS Water molecules dissociate into ions. Forming hydrogen ions (H+) and hydroxide ions (OH-) Acidity or Alkalinity is a measure of the relative amounts of (H+) and (OH-) dissolved in a solution.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ACIDS, BASES, and pH ACIDS  A compound that forms H+ ions in a solution, contain higher concentrations of H+ ions. BASES  A compound that produces OH- in a solution, contain lower concentrations of H+ ions pH scale  used to indicate the amount of H+ ions in a solution. 1.Ranges from 0 – Below 7  Acid 3.Greater 7  Base

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

BUFFERS Substances that resist changes in pH. Controlling pH  important in maintaining homeostasis Most cells in the human body must generally be kept between a pH of 6.5 and 7.5.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bell Ringer Differentiate between acids and bases. What role do buffers play in maintaining homeostasis?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Upcoming Assignments & Due Dates 3 Day Food Diary: Due Monday 11/24 Biochemistry Study Guide: Due Monday 12/1 Biochemistry Quiz: Due Monday 12/1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Household Products Lemon Juice Water Lysol Bleach Ammonia Mouthwash Hydrogen Peroxide Hand Sanitizer Baby Oil Epsom Salt