CAPTERS 2 & 3 The Chemical Context of Life Chapter 2: Atoms and Molecules Chapter 3: Water & p
Chapter 2: Atoms and Molecules Chapter Reading pp. 29-41
The Elements of Life
Atoms & Nucleus 2e Electron cloud Subatomic Particles elium Electron cloud 6e 2 2 Protons Neutrons Mass number = 4 2 Electrons Nucleus Carbon atomic number = # of protons 6 6 6 Protons Neutrons Electrons Mass number = 12 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 *
Electron Orbitals orbitals are geometrically arranged regions of space around an atomic nucleus in which electrons are found each orbital can hold no more than 2 electrons orbitals are arranged in groups at distinct energy levels called electron shells Neon, with two filled Shells (10 electrons) (a) Electron distribution diagram First shell Second shell First shell Second shell z 1s orbital 2s orbital Three 2p orbitals (b) Separate electron orbitals 1s, 2s, and 2p orbitals (c) Superimposed electron orbitals x y
Energy Levels of Electrons (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 First shell (lowest energy level) Energy lost (b) Atomic nucleus
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 2 e 4.00 Atomic number Element symbol Electron distribution diagram elium 2e Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Second shell Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Third shell
ydrogen atoms (2 ) The Formation of Molecules 2 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 ydrogen molecule ( 2 ) jonic bonds involve the donation/acceptance of such electrons
Name and Molecular Formula Electron Distribution Diagram Lewis Dot Structure and Structural Formula Space- Filling Model Representing Molecular (a) ydrogen ( 2 ) Structure (b) Oxygen (O 2 ) (c) Water ( 2 O) (d) Methane (C 4 )
Geometry of Covalent Bonds z s orbital Three p orbitals x y (a) ybridization of orbitals Four hybrid orbitals Tetrahedron The basic arrangement of covalent bonds and electron pairs around CARBON, OXYGEN, NITROGEN and many other atoms is a tetrahedron Space-Filling Model Water ( 2 O) Ball-and-Stick Model ybrid-orbital Model (with ball-and-stick model superimposed) Unbonded Electron 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- O polar bonds occur between atoms with significantly different electronegativities due to unequal sharing of e- + + 2 O
Non-polar Molecules electrons are shared equally between identical atoms since their attraction for electrons (electronegativity) is the same
Polar Molecules NON-POLAR POLAR C & electronegativies are ~ the same O & 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 ( 2 O) ammonia (N 3 ) + + + + ydrogen bond + atom bound to a more electronegative atom (e.g., N or O) - charge on atom of another molecule or chemical group
Ions and Ionic Bonds Na Sodium atom Cl Chlorine atom Electronic transfer forms ions Ionic bond + Na + Sodium ion (a cation) Cl Chloride ion (an anion) sodium chloride (NaCl) crystal Na + Cl opposing ions form neutral salts
Chemical Reactions 2 2 O 2 2 2 O 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
Water is a Polar Molecule Covalent bonds between O & are polar. Water s polarity gives it unique properties: is a good solvent for polar, charged substances O + + 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 + + O +
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
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 SOLVENT liquid in which a substance is dissolved Ion in solution Salt crystal SOLUTE 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 O O O O 2 2 O ydronium ion ( 3 O + ) ydroxide ion (O ) By convention, the hydronium ion is represented as a hydrogen ion ( + ): 2 O + + O - in pure water there will be equal concentrations of these two ions making it a neutral solution, though water is rarely pure
Acids and Bases 0 Acidic [ + ] > [O ] Acids donate + in aqueous solutions Neutral [ + ] = [O ] 7 Basic [ + ] < [O ] Bases donate O or accept + in aqueous solutions 14
Increasingly BASIC (Lower concentration of + ) Increasingly ACIDIC (igher concentration of + ) p scale 0 1 Battery acid 2 Lemon juice, gastric juice p is a measure of [ + ] Acidic solution 3 4 Grapefruit juice, soft drink, vinegar, beer Tomato juice p = - log [+] Neutral solution NEUTRAL [ + ]=O ] 5 6 7 8 9 Rain water uman urine Saliva Pure water uman blood, tears Seawater each p unit reflects a 10-fold difference in + concentration [ + ] lower p = higher [ + ] (and vice versa) 10 11 12 Milk of magnesia ousehold ammonia p 3 = 10-3 M = 0.001 M [ + ] p 9 = 10-9 M = 0.000000001 M [ + ] ousehold bleach 13 Oven cleaner M = moles per liter Basic solution 14
Key Terms for Chapters 2 & 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 2 Questions 1-9 Relevant Chapter 3 Questions 1-4, 6