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1 (c) The McGraw-Hill Companies, Inc. Chapter 2BiologySixth EditionRaven/Johnson(c) The McGraw-Hill Companies, Inc.
2 Matter is anything that takes up space and has weight. All matter, living or nonliving, is made up of elementsElements contain atoms, the smallest unit of matter that can enter chemical reactions.
3 Atoms have a central nucleus made up of protons (+) and neutrons (o), and shells around the nucleus in which electrons (-) orbit.Fig 2.2
4 The atomic number = number of protons (# of protons determines the element). protons bear a positive electrical chargeThe atomic weight = number of protons plus number of neutrons.neutrons bear no electrical chargeelectrons bear a negative electrical chargeAn electrically neutral atom means:number of protons = number of electrons
5 Atoms have an atomic symbol, atomic number, and atomic mass. Some atoms differ in their number of neutrons and are called isotopes.Carbon has 3 isotopes:Carbon 12 (most abundant)Carbon 13Carbon 14 (radioactive - unstable)
7 Review of an Atom 3 10 4 1 2 e- in inner shell 8 e- in outer shell 10 e- TOTAL9510 neutrons10 protons20 atomic mass unitsElement = Ne (Neon)Atomic numberNeAtomic mass 208267# of protons determine element
8 Chemical Behavior of Atoms Because an atom’s electrons are relatively far from the nucleus, the nuclei of two atoms never come close enough in nature to interact with each other. Therefore, an atoms electrons determine its chemical behavior.
9 Electron Orbital vs. Energy Level Electron Orbital – The area around a nucleus that an electron is most likely to be found.Electron Energy Level – The potential energy of an electron is directly related to the distance between an electron and the nucleus.Energy – the ability to do work
15 Important Atom Characteristics Electrons in the outermost energy level are called valence electrons.These are the electrons that determine the atoms chemistryOctet rule (rule of eight) – For most atoms important to life, the outer energy level can contain no more than eight electrons.
16 Fig 2.6Oxidation – The loss of an electron (atom becomes electrically positive)Reduction – The gain of an electron (atom becomes electrically negative)
17 Chemical Bonds Build Molecules Bonds between atoms can either be ionic, covalent, or hydrogen.Ionic and covalent bonds are the result of interactions among electrons.Hydrogen bonds are attractions between weakly positive and weakly negatively charged particles.
18 Fig 2.9In ionic bonding, atoms either give up or accept electrons, resulting in ions (electrically charged atoms/non-neutral). Ions with opposite charges (- or +) are attracted to each other and form an ionic bond. (Opposite charges attract, + is attracted to -, - is attracted to +).
25 Important Properties of Water Cohesion (liquid) / Adhesion (polarity)High Specific Heat (maintain temperature)High Heat of Vaporization (cools body)Lower Density of Ice (water bodies)High Polarity / Water as a Solvent
30 Water IonizesWater dissociates and releases hydrogen ions (H+) and hydroxide ions (OH-).
31 Concentrations of hydrogen ions or hydroxide ions can be represented using the pH scale. moles/liter1 x 10 –6 [H+] = pH 61 x 10 –7 [H+] = pH 71 x 10 –8 [H+] = pH 8*A mole is the atomic weight of a molecule weighed out in grams. Atomic weight of H+ is one.
33 Acids are molecules that release hydrogen ions in solution (usually water). HCl H+ + Cl-Bases are molecules that either take up hydrogen ions or give off hydroxide ions in solution.NaOH Na+ + OH-Hydroxide ion