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Chapter 2 Atoms and Molecules: The Chemical Basis of Life Inorganic vs. Organic Inorganic compounds - simple substances that do not contain carbon Ex. water Organic compounds – carboncontaining compounds that are large and complex Ex. Glucose Organic compounds all contain: Ca r c 0% bo n 0% Zin 6% en 4. Ni tro g 3. 94% n 2. Oxygen Nitrogen Carbon Zinc Ox yg e 1. Elements Elements – substances that cannot be broken down into simpler substances 4 elements responsible for more than 96% of the mass of most organisms: Oxygen Carbon Hydrogen Nitrogen See table 2-1 in book p.24 Other elements that make up living organisms Calcium Phosphorus Potassium Magnesium Sodium Iron Sulfur What is the most abundant element in the human body? 12% en Ni tro g Hy dr og en 6% bo n 4. 29% Ca r 3. 53% n 2. Oxygen Carbon Hydrogen Nitrogen Ox yg e 1. Chemistry Quick Review Atom – the smallest portion of an element that retains its chemical properties Subatomic particles: Electron – negative charge Proton – positive charge Neutron – uncharged # of electrons = # of protons Nucleus – protons and neutrons Electrons – move rapidly through space around nucleus Atomic Number Each kind of element has a fixed number of protons in the atomic nucleus Written as a subscript to the left of the chemical symbol Example: 8O Oxygen nucleus contains 8 protons Determines the atom’s identity and defines the element Which element has an atomic number of 7? He liu m 0% en 0% Ni tro g 0% bo n 4. Ca r 3. og en 2. Hydrogen Carbon Nitrogen Helium Hy dr 1. 100% The Periodic Table Chart in which elements are arranged in order by atomic number Can be used to determine electron configurations Bohr model – shows the electrons arranged in a series of concentric circles around the nucleus Bohr Model What element is this? Atomic Mass Mass of protons + neutrons Mass of electron = 1/1800 the mass of a proton or neutron Atomic mass number is a superscript to the left of the symbol Example: 16O Isotopes Atom with different number of neutrons (different masses) Most elements mixture of isotopes Ex. Carbon-12, Carbon-14 Mass of element is average of the masses of its isotopes Atomic mass of Carbon = 12.011 Isotopes Radioisotopes – unstable isotopes Tend to break down (decay) to a more stable isotope Emit radiation when they decay Ex. Carbon-14 decays to Nitrogen Electrons move in orbitals Orbitals are more like “electron clouds” The farther away from the nucleus, the more energy the electrons have Valence electrons – the most energetic electrons Occupy valence (outer) shell Chemical Reactions Valence electrons participate in chemical reactions When valence shell is full, it is stable When valence shell is not full, atoms tend to lose, gain, or share electrons To be full, the first electron shell has how many electrons? 0% 0% 6% 0% 18 5. 8 4. 4 3. 94% 2 2. 1 2 4 8 18 1 1. Compounds and Molecules Atoms combine to form compounds and molecules Compounds - 2 or more different elements combined in a fixed ratio Ex. NaCl (table salt) Molecules - 2 or more atoms combine chemically Ex. O2, DNA Are all molecules compounds? 71% 29% No 2. Yes No Ye s 1. Molecule or Compound? O2 24% Bo th Co m po un d le 12% cu 3. ol e 2. Molecule Compound Both M 1. 65% Chemical Formulas Represents chemical composition Simplest formula – most simple ratio Molecular formula – actual numbers of each type of atom per molecule Ex. NH2 Ex. N2H4 Structural formula – shows arrangement of atoms Ex. Water H–O–H Chemical Equations Reactants – participate in reaction Products – formed by the reaction Example – cellular respiration C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy Chemical Bonds Valence electrons dictate # of bonds 2 types of chemical bonds: Covalent – atoms share electrons Ionic - attraction between positive cations and negative anions Transfer electrons Covalent Bonds Ex. H2 gas Each atom has 1 electron 2 electrons fill valence shell Both atoms attract the electrons (share) Valence shell is full w/ 2 electrons Types of Covalent Bonds Single covalent bond – 1 pair of electrons is shared Double covalent bond – 2 pairs of electrons shared Triple covalent bond – 3 pairs of electrons shared Covalent Bonds Electronegativity - measure of atom’s attraction for shared electrons in chemical bonds Oxygen, Nitrogen, Fluorine, Chlorine very electronegative Can be polar or nonpolar Similar electronegativities = nonpolar bonds Different electronegativities = polar bonds Electrons are pulled closer to the nucleus of the atom with the higher electronegativity Polar Molecules Molecule with one or more polar covalent bonds One end with a partial positive charge and other end a partial negative charge Ex. Water (p.31) A water molecule is polar because 24% .. ll . ta or bi el Th e Th e el ec tro ns ec tro ns or bi or bi tt tt he he ... ... 0% ct ro ns 3. 76% el e 2. The electrons orbit the H atoms more closely The electrons orbit the O atom more closely The electrons orbit all atoms equally Th e 1. Ionic Bonds Ionic compound – consists of anions and cations bonded together Ex. NaCl (p.31 & 32) Na – 1 valence electron Cl – 7 valence electrons Cl takes electron from Na to complete valence shell Hydrogen Bonds Weak attractions Important in determining the 3-D structure of large molecules DNA Proteins Why are hydrogen bonds essential to the function of DNA? 33% n. .. st ro ar Th ey lo al Th ey e w th th e. .. e. .. 33% ep 3. 33% ke 2. They keep the 2 strands tightly bonded together They allow the 2 strands to separate for replication They are strong bonds Th ey 1. Redox Reactions Reaction that involves electron transfer Cellular Respiration and Photosynthesis Oxidation – atom/ion loses electron Reduction – atom/ion gains electron Water 70% of total body weight Reactant/product in many chemical reactions Solvent for most biological reactions Hydrophilic – react with water Hydrophobic – not disrupted/dissolved by water Which of the following substances is hydrophobic? 33% Oi l 33% Su ga r 3. t 2. Salt Sugar Oil Sa l 1. 33% Properties of Water Cohesive – water molecules stick to each other Adhesive – water molecules stick to other substances Capillary action – cohesion and adhesion working together Water will move against gravity in a narrow tube In plants, water moves from soil to roots Properties of Water Surface tension – water molecules crowd together at the surface High specific heat strong layer Maintains a stable temperature High heat of vaporization Much heat required to change to water vapor Acids and Bases Acids – proton donors Acid -> H+ + Anion Acidic solutions have higher hydrogen ion concentration Turn blue litmus paper red Sour taste HCl – inorganic acid Acetic Acid – from vinegar, Lactic Acid – from sour milk (organic acids) Acids and Bases Bases – proton acceptors Base -> OH- + Cation Basic solutions have lower hydrogen ion concentration Turn red litmus paper blue Feel slippery to the touch Ex. Sodium Hydroxide, Ammonia – inorganic Purine and Pyrimidine – organic pH scale Logarithmic expression of the hydrogen ion concentration of solution 7 = neutral Below 7 = Acid Above 7 = Base