CAPTERS & 3 The Chemical Context of Life Chapter : Atoms and Molecules Chapter 3: Water & p Chapter : Atoms and Molecules Chapter Reading pp. 9-41 The Elements of Life 1
Atoms & Subatomic Particles Nucleus elium e cloud cloud 6e Protons Neutrons Mass number = 4 s Nucleus Carbon atomic number = # of protons 6 6 6 Protons Neutrons s Mass number = 1 mass number = # of neutrons & protons Isotopes Atoms of the same element having different numbers of neutrons are referred to as different isotopes, some of which are unstable and thus radioactive. radioactive emissions are of different types depending on the isotope (a particles, b particles, x-rays, g-rays) each radioactive isotope has a characteristic half-life * b emitter * rbitals orbitals are geometrically arranged regions of space around an atomic nucleus in which electrons are found each orbital can hold no more than electrons orbitals are arranged in groups at distinct energy levels called electron shells Neon, with two filled Shells (10 electrons) (a) distribution diagram First shell Second shell First shell Second shell z 1s orbital s orbital Three p orbitals (b) Separate electron orbitals 1s, s, and p orbitals (c) Superimposed electron orbitals x y
Energy Levels of s (a) A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons Third shell (highest energy level) Second shell (higher energy level) Energy absorbed (b) First shell (lowest energy level) Atomic nucleus Energy lost The Periodic Table elements in the same column have the same number of valence electrons, and similar chemical properties First shell ydrogen 1 Mass number e 4.00 Atomic number Element symbol distribution diagram elium e Second shell Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N xygen 8 Fluorine 9F Neon 10Ne Third shell Sodium 11Na Magnesium 1Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar ydrogen atoms ( ) ydrogen molecule ( ) The Formation of Molecules or more atoms connected by a chemical bond(s) constitute a molecule chemical bonds involve unpaired electrons from each atom involved in the bond covalent bonds involve the sharing of such electrons jonic bonds involve the donation/acceptance of such electrons 3
Name and Molecular Formula (a) ydrogen ( ) Distribution Diagram Lewis Dot Structure and Structural Formula Space- Filling Model Representing Molecular Structure (b) xygen ( ) (c) Water ( ) (d) Methane (C 4) Geometry of Covalent Bonds z Four hybrid orbitals s orbital Three p orbitals x y Tetrahedron (a) ybridization of orbitals The basic arrangement of covalent bonds and electron pairs around CARBN, XYGEN, NITRGEN and many other atoms is a tetrahedron Space-Filling Model Water ( ) Ball-and-Stick ybrid-rbital Model Model (with ball-and-stick model superimposed) Unbonded pair this basic geometric arrangement is altered with double or triple bonds Methane (C 4) (b) Molecular-shape models Polarity in Covalent Bonds The sharing of electrons in covalent bonds is not necessarily equal, depending on the electronegativity of the atoms involved in the bond: non-polar bonds occur between atoms of the same or similar electronegativities due to equal sharing of e- polar bonds occur between atoms with significantly different electronegativities due to unequal sharing of e- 4
Non-polar Molecules electrons are shared equally between identical atoms since their attraction for electrons (electronegativity) is the same Polar Molecules NN-PLAR PLAR C & electronegativies are ~ the same & electronegativities are significantly different elements tend to vary in their electronegativities if atoms sharing electrons differ significantly in electronegativity, the electrons are shared unequally and the bond is polar Polarity & ydrogen Bonds ydrogen bonds are weak interactions that occur between atoms involved in polar covalent bonds, one of which is a hydrogen atom: water ( ) ammonia (N 3 ) ydrogen bond atom bound to a more electronegative atom (e.g., N or ) - charge on atom of another molecule or chemical group 5
Na Sodium atom Ions and Ionic Bonds Cl Chlorine atom ic transfer forms ions Ionic bond + Na + Sodium ion (a cation) Cl Chloride ion (an anion) Na + sodium chloride (NaCl) crystal Cl opposing ions form neutral salts Chemical Reactions Reactants Reaction Products Covalent bonds in reactant molecules break and the atoms form new covalent bonds in the products all atoms from reactants end up in products chemical reactions are reversible, direction depends on conditions, concentrations of products vs reactants Chapter 3: Water & p Chapter Reading pp. 45-53 6
Water is a Polar Molecule Covalent bonds between & are polar. Water s polarity gives it unique properties: is a good solvent for polar, charged substances high specific heat requires a lot of energy to change its temperature liquid in a broad temperature range high heat of vaporization ydrogen between Water Molecules Cohesion between water molecules via hydrogen bonds ydrogen bond Water s Properties are due to -bonds e.g., its unusually high freezing, boiling temperatures ydrogen bond ICE ydrogen bonds are stable LIQUID WATER ydrogen bonds constantly break and re-form 7
Water is a Good Solvent Due to interactions between opposing charges in water and other polar or charged molecules non-polar (hydrophobic) molecules do not dissolve well in water SLVENT liquid in which a substance is dissolved Ion in solution Salt crystal SLUTE a substance dissolved in liquid Macromolecules in Water (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein s surface attract water molecules. hydrophilic portions of macromolecules are polar or charged and are exposed to the aqueous solvent hydrophobic portions of macromolecules are non-polar and buried inside the molecule, away from water Dissociation of Water Molecules ydronium ion ( 3 + ) ydroxide ion ( ) By convention, the hydronium ion is represented as a hydrogen ion ( + ): + + - in pure water there will be equal concentrations of these two ions making it a neutral solution, though water is rarely pure 8
Increasingly BASIC (Lower concentration of + ) Increasingly ACIDIC (igher concentration of + ) /7/016 Acids and Bases 0 Acidic [ + ] > [ ] Acids donate + in aqueous solutions Neutral [ + ] = [ ] 7 Basic [ + ] < [ ] Bases donate or accept + in aqueous solutions 14 Acidic solution p scale 0 1 Battery acid Lemon juice, gastric juice 3 Grapefruit juice, soft drink, vinegar, beer 4 Tomato juice p is a measure of [ + ] p = - log [+] Neutral solution NEUTRAL [ + ]= ] 5 Rain water 6 uman urine Saliva 7 Pure water uman blood, tears 8 Seawater 9 each p unit reflects a 10-fold difference in + concentration [ + ] lower p = higher [ + ] (and vice versa) 10 Milk of magnesia 11 ousehold ammonia 1 p 3 = 10-3 M = 0.001 M [ + ] p 9 = 10-9 M = 0.000000001 M [ + ] ousehold bleach 13 ven cleaner M = moles per liter Basic solution 14 Key Terms for Chapters & 3 protons, neutrons, electrons orbitals, electron shells, isotope ions, covalent bonds, ionic bonds polar, non-polar, hydrogen bond electronegativity solvent, solute, p, buffer acid vs base, acidic vs basic specific heat, heat of vaporization Relevant Chapter Questions 1-9 Relevant Chapter 3 Questions 1-4, 6 9