CHAPTER 2Basic Atomic StructureElements – The Building Blocks of Chemical EvolutionPowerPoint PresentationElectron Arrangement around the NucleusChemical BondingCovalent BondsSlide 8Ions and Ionic BondsHow Many Bonds Can an Atom Have?Slide 11Representing MoleculesSlide 13Chemical ReactionsQuantifying MoleculesWhy Is Water Such an Efficient Solvent?Slide 17Water and Hydrogen BondsSlide 19Correlation of Water’s Structure and PropertiesA Closer Look at the Properties of WaterSlide 22Acid–Base Reactions and pHThe pH Scale and BuffersSlide 25Chemical Evolution TheoryHow Do Chemical Reactions Happen?What Is Energy?Potential Energy and Kinetic EnergyRevisiting the Theory of Chemical EvolutionEarly Origin-of-Life ExperimentsSlide 32Slide 33Slide 34Heat and the First Law of ThermodynamicsSlide 36What Makes a Chemical Reaction Spontaneous?The Second Law of ThermodynamicsSlide 39Slide 40Gibbs Free-Energy ChangeTemperature and Concentration Affect ReactionsSlide 43Slide 44Slide 45Energy Inputs and the Start of Chemical EvolutionSlide 47Chemical Energy Is a Form of Potential EnergyThe Importance of CarbonSlide 50Slide 51Functional Groups: Determinants of Chemical BehaviorSlide 53Slide 54© 2011 Pearson Education, Inc.CHAPTER 2© 2011 Pearson Education, Inc.Basic Atomic Structure•Atoms are composed of:–Protons – positively charged particles–Neutrons – neutral particles–Electrons – negatively charged particles•Protons and neutrons are located in the nucleus.•Electrons are found in orbitals surrounding the nucleus.© 2011 Pearson Education, Inc. Elements – The Building Blocks of Chemical Evolution •Every different atom has a characteristic number of protons in the nucleus, called the atomic number.•Atoms with the same atomic number have the same chemical properties and belong to the same element.•Forms of an element with different numbers of neutrons are isotopes.•The mass number is the number of protons + neutrons of the most common isotope.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Electron Arrangement around the Nucleus•Electrons move around atomic nuclei in specific regions called orbitals.–Each orbital can hold up to two electrons.•Orbitals are grouped into levels called electron shells. –Electron shells are numbered, with smaller numbers closer to the nucleus. –The electrons in the outermost shell are called valence electrons.•Elements commonly found in organisms have at least one unpaired valence electron. The number of unpaired electrons in an atom is its valence.© 2011 Pearson Education, Inc.Chemical Bonding•Unfilled electron orbitals allow formation of chemical bonds, and atoms are most stable when each electron orbital is filled. –Covalent bond: Each atom’s unpaired valence electrons are shared by both nuclei to fill their orbitals.–Substances held together by covalent bonds are called molecules. –Ionic bond: Electrons are transferred from one atom to another.© 2011 Pearson Education, Inc.Covalent Bonds•Electrons are not always shared equally. An atom in a molecule with a high electronegativity will hold the electrons more tightly and have a partial negative charge (δ–), whereas the other atom will have a partial positive charge (δ+).•Differences in electronegativity dictate how electrons are distributed in covalent bonds.–Nonpolar covalent bond: Electrons are evenly shared between two atoms and the bond is symmetrical.–Polar covalent bond: Electrons are asymmetrically shared.© 2011 Pearson Education, Inc.file:///Users/ericarowe/Documents/UTK%20Biology/UTK%20Bio140%20Fall%202011/Chapter_02/A_PowerPoint_Lecture_Tools/02_Lecture_Outline/Covalent_Bonds.html© 2011 Pearson Education, Inc.Ions and Ionic Bonds•An atom or molecule that carries a charge is called an ion.–Cation: An atom that loses an electron and becomes positively charged.–Anion: An atom that gains an electron and becomes negatively charged.•The resulting attraction between oppositely charged ions is an ionic bond.© 2011 Pearson Education, Inc.How Many Bonds Can an Atom Have?•The number of unpaired electrons determines the number of bonds an atom can make.•Atoms with more than one unpaired electron can form multiple single bonds or double or triple bonds.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Representing Molecules •The shape of a simple molecule is governed by the geometry of its bonds.•Molecular formulas indicate the numbers and types of atoms in a molecule (e.g., H2O, CH4).•Structural formulas indicate which atoms are bonded together and whether the bonds are single, double, or triple bonds. •Ball-and-stick models and space-filling models show 3D geometry.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Chemical Reactions•Chemical reactions occur when:1. One substance is combined with another. –Atoms are rearranged in molecules, or small molecules combine to form larger molecules. 2. One substance is broken down into another substance. –Molecules are split into atoms or smaller molecules. •In most cases, chemical bonds are broken and new bonds form.© 2011 Pearson Education, Inc.Quantifying Molecules•The molecular weight of a molecule is the sum of the mass numbers of all the atoms in the molecule.•One mole, or 6.022  1023 molecules, has a mass equal to the molecular weight expressed in grams.•The concentration of a substance in a solution is typically expressed as molarity (M), which is the number of moles per liter.© 2011 Pearson Education, Inc.Why Is Water Such an Efficient Solvent?•Life is based on water because water is a great solvent.•The covalent bonds in water are polar because oxygen has a greater electronegativity than hydrogen.–Oxygen has a partial negative charge. –Hydrogen has a partial positive charge.•Hydrogen bonds are the weak electrical attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule.–Can also form between a water molecule and another polar molecule.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Water and Hydrogen Bonds•Ions and polar molecules stay in solution because of their interactions with water’s partial charges. These atoms and molecules are said to be hydrophilic.•Uncharged and nonpolar compounds do not dissolve in water and are said to be hydrophobic.Hydrogen bonding makes it possible for almost any