Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 2 The Chemical Context of Life
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Elements and Compounds An element is a substance that cannot be broken down to other substances by chemical reactions A compound is a substance consisting of two or more elements in a fixed ratio SodiumChlorineSodium chloride
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Essential Elements of Life Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter Trace elements are those required by an organism in minute quantities
LE 2-3 Nitrogen deficiencyIodine deficiency
LE 2-4 Nucleus Electrons Cloud of negative charge (2 electrons)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Atomic Number and Atomic Mass Atoms of the various elements differ in number of subatomic particles – Atomic number – Mass number – Atomic mass
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Isotopes Atoms of an element have the same number of protons but may differ in number of neutrons some are radioactive
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some applications of radioactive isotopes in biological research: – Dating fossils – Tracing atoms through metabolic processes – Diagnosing medical disorders
LE 2-5a Ingredients including radioactive tracer (bright blue) Incubators Human cells DNA (old and new) °C 25°C 40°C 15°C 30°C 45°C 20°C 35°C 50°C TECHNIQUE
LE 2-5b
LE 2-5c Optimum temperature for DNA synthesis RESULTS Counts per minute (x 1,000) Temperature (°C)
LE 2-6 Cancerous throat tissue
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Energy Levels of Electrons Energy is the capacity to cause change Potential energy is the energy that matter has because of its location or structure electron shell A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons.
LE 2-7b Third energy level (shell) Second energy level (shell) First energy level (shell) Atomic nucleus Energy absorbed Energy lost
LE 2-8 First shell Hydrogen 1 H Lithium 3 Li Second shell Third shell Sodium 11 Na Beryllium 4 Be Magnesium 12 Mg Boron 5 B Aluminum 12 Al Silicon 14 Si Carbon 6 C Nitrogen 7 N Phosphorus 15 P Oxygen 8 O Sulfur 16 S Chlorine 17 Cl Fluorine 9 F Neon 10 Ne Argon 18 Ar Helium 2 He Atomic number Element symbol Electron-shell diagram Atomic mass 2 He 4.00
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electron Orbitals An orbital is the three-dimensional space where an electron is found 90% of the time
LE 2-9 Electron orbitals Electron-shell diagrams 1s orbital2s orbitalThree 2p orbitals1s, 2s, and 2p orbitals First shell (maximum 2 electrons) Second shell (maximum 8 electrons) Neon, with two filled shells (10 electrons) x z y
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Covalent Bonds A covalent bond is the sharing of a pair of valence electrons by two atoms Hydrogen atoms (2 H) Hydrogen molecule (H 2 )
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A molecule consists of two or more atoms held together by covalent bonds – single covalent bond – double covalent bond Animation: Covalent Bonds Animation: Covalent Bonds Oxygen (O 2 )
LE 2-11c Water (H 2 O) Name (molecular formula) Electron- shell diagram Structural formula Space- filling model
LE 2-11d Methane (CH 4 ) Name (molecular formula) Electron- shell diagram Structural formula Space- filling model
LE 2-12 H O H H2OH2O ++ ++ ––
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ionic Bonds Atoms sometimes strip electrons from their bonding partners – Example: sodium to chlorine Na Sodium atom (an uncharged atom) Cl Chlorine atom (an uncharged atom) Na + Sodium ion (a cation) Cl – Chlorine ion (an anion) Sodium chloride (NaCl)
LE 2-8 First shell Hydrogen 1 H Lithium 3 Li Second shell Third shell Sodium 11 Na Beryllium 4 Be Magnesium 12 Mg Boron 5 B Aluminum 12 Al Silicon 14 Si Carbon 6 C Nitrogen 7 N Phosphorus 15 P Oxygen 8 O Sulfur 16 S Chlorine 17 Cl Fluorine 9 F Neon 10 Ne Argon 18 Ar Helium 2 He Atomic number Element symbol Electron-shell diagram Atomic mass 2 He 4.00
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An anion is a negatively charged ion A cation is a positively charged ion An ionic bond is an attraction between an anion and a cation Animation: Ionic Bonds Animation: Ionic Bonds Na + Cl –
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Weak Chemical Bonds Weak chemical bonds reinforce shapes of large molecules and help molecules adhere to each other – Ionic bonds – Hydrogen bonds – Van der Waals Interactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen Bonds –– Water (H 2 O) Ammonia (NH 3 ) Hydrogen bond ++ ++ –– ++ ++ ++
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Van der Waals Interactions Molecules or atoms that are very close together can be attracted by fleeting charge differences
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Shape and Function A molecule’s shape is usually very important to its function – determined by the positions of its atoms’ valence orbitals s orbital z x y Three p orbitals Four hybrid orbitals Tetrahedron Hybridization of orbitals
LE 2-16b Space-filling model Ball-and-stick model Hybrid-orbital model (with ball-and-stick model superimposed) Unbonded electron pair Water (H 2 O) Methane (CH 4 ) Molecular shape models 104.5°
LE 2-17a Natural endorphin Morphine Carbon Hydrogen Nitrogen Sulfur Oxygen Structures of endorphin and morphine
LE 2-17b Natural endorphin Morphine Brain cell Endorphin receptors Binding to endorphin receptors
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 2.4: Chemical reactions make and break chemical bonds The starting molecules of a chemical reaction are called reactants The final molecules of a chemical reaction are called products ReactantsReactionProducts 2 H 2 OO2O2 2 H 2
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