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Life’s Chemical Basis

Life’s Chemical Basis. Chapter 2 Hsueh-Fen Juan ( 阮雪芬 ) Sep. 18, 2012. Video: What are you worth?. Impacts, Issues: What Are You Worth?. Fifty-eight elements make up the human body. 1.1 Start With Atoms.

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Life’s Chemical Basis

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  1. Life’s Chemical Basis Chapter 2 Hsueh-Fen Juan (阮雪芬) Sep. 18, 2012

  2. Video: What are you worth?

  3. Impacts, Issues:What Are You Worth? • Fifty-eight elements make up the human body

  4. 1.1 Start With Atoms • The behavior of elements, which make up all living things, starts with the structure of individual atoms

  5. Characteristics of Atoms • Atomsare the building blocks of all substances • Made up of electrons, protons and neutrons • Electrons (e-) have a negative charge • Move around the nucleus • Chargeis an electrical property • Attracts or repels other subatomic particles

  6. Characteristics of Atoms • Thenucleuscontains protons and neutrons • Protons(p+) have a positive charge • Neutrons have no charge • Atoms differ in number of subatomic particles • Atomic number (number of protons) determines the element • Elements consist only of atoms with the same atomic number

  7. Characteristics of Atoms • Isotopes • Different forms of the same element, with different numbers of neutrons • Mass number • Total protons and neutrons in a nucleus • Used to identify isotopes

  8. Atoms

  9. The Periodic Table • Periodic table of the elements • An arrangement of the elements based on their atomic number and chemical properties • Created by Dmitry Mendeleev

  10. Periodic Table of the Elements

  11. 2.2 Putting Radioisotopes to Use • Some radioactive isotopes – radioisotopes – are used in research and medical applications

  12. Radioisotopes • Henri Becquerel discovered radioisotopes of uranium in the late 1800s • Radioactive decay • Radioisotopes emit subatomic particles of energy when their nucleus breaks down, transforming one element into another at a constant rate • Example:14C →14N

  13. Tracers • Tracer • Any molecule with a detectable substance attached • Examples: • CO2 tagged with 14C used to track carbon through photosynthesis • Radioactive tracers used in medical PET scans

  14. PET Scanning

  15. Animation: PET scan

  16. 2.1-2.2 Key Concepts:Atoms and Elements • Atoms are particles that are the building blocks of all matter; they can differ in numbers of protons, electrons, and neutrons • Elements are pure substances, each consisting entirely of atoms with the same number of protons

  17. 2.3 Why Electrons Matter • Atoms acquire, share, and donate electrons • Whether an atom will interact with other atoms depends on how many electrons it has

  18. Atoms and Energy Levels • Electrons move around nuclei in orbitals • Each orbital holds two electrons • Each orbital corresponds to an energy level • An electron can move in only if there is a vacancy vacancy no vacancy

  19. Why Atoms Interact • Theshell modelof electron orbitals diagrams electron vacancies; filled from inside out • First shell: one orbital (2 electrons) • Second shell: four orbitals (8 electrons) • Third shell: four orbitals (8 electrons) • Atoms with vacancies in their outer shell tend to give up, acquire, or share electrons

  20. Shell Models

  21. Animation: The shell model of electron distribution

  22. Atoms and Ions • Ion • An atom with a positive or negative charge due to loss or gain of electrons in its outer shell • Examples: Na+, Cl- • Electronegativity • A measure of an atom’s ability to pull electrons from another atom

  23. Ion Formation

  24. Animation: How atoms bond

  25. From Atoms to Molecules • Chemical bond • An attractive force existing between two atoms when their electrons interact • Molecule • Two or more atoms joined in chemical bonds

  26. Combining Substances • Compounds • Molecules consisting of two or more elements whose proportions do not vary • Example: Water (H2O) • Mixture • Two or more substances that intermingle but do not bond; proportions of each can vary

  27. A Compound: Water

  28. 2.3 Key Concepts:Why Electrons Matter • Whether one atom will bond with others depends on the element, and the number and arrangement of its electrons

  29. 2.4 What Happens When Atoms Interact? • The characteristics of a bond arise from the properties of the atoms that participate in it • The three most common types of bonds in biological molecules are ionic, covalent, and hydrogen bonds

  30. Different Ways to Represent the Same Molecule

  31. Ionic Bonding • Ionic bond • A strong mutual attraction between two oppositely charges ions with a large difference in electronegativity (an electron is not transferred) • Example: NaCl (table salt)

  32. Ionic Bonds

  33. Animation: Ionic bonding

  34. Covalent Bonding • Covalent bond • Two atoms with similar electronegativity and unpaired electrons sharing a pair of electrons • Can be stronger than ionic bonds • Atoms can share one, two, or three pairs of electrons (single, double, or triple covalent bonds)

  35. Characteristics of Covalent Bonds • Nonpolar covalent bond • Atoms sharing electrons equally; formed between atoms with identical electronegativity • Polar covalent bond • Atoms with different electronegativity do not share electrons equally; one atom has a more negative charge, the other is more positive

  36. Polarity • Polarity • Separation of charge intodistinct positive and negative regions in a polar covalent molecule • Example: Water (H2O)

  37. Covalent Bonds

  38. Animation: Covalent bonds

  39. Hydrogen Bonding • Hydrogen bond • A weak attraction between a highly electronegative atom and a hydrogen atom taking part in a separate polar covalent bond • Hydrogen bonds do not form molecules and are not chemical bonds • Hydrogen bonds stabilize the structures of large biological molecules

  40. Hydrogen Bonds

  41. Animation: Examples of hydrogen bonds

  42. 2.4 Key Concepts:Atoms Bond • Atoms of many elements interact by acquiring, sharing, and giving up electrons • Ionic, covalent, and hydrogen bonds are the main interactions between atoms in biological molecules

  43. 2.5 Water’s Life-Giving Properties • Living organisms are mostly water; all the chemical reactions of life are carried out in water • Water is essential to life because of its unique properties • The properties of water are a result of extensive hydrogen bonding among water molecules

  44. Polarity of the Water Molecule • Overall, water (H2O) has no charge • The water molecule is polar • Oxygen atom is slightly negative • Hydrogen atoms are slightly positive • Hydrogen bonds form between water molecules • Gives water unique properties

  45. Water: Essential for Life Fig. 2-10a, p. 28

  46. Water: Essential for Life Fig. 2-10b, p. 28

  47. Water: Essential for Life Fig. 2-10c, p. 28

  48. Animation: Structure of water

  49. Water’s Solvent Properties • Solvent • A substance (usually liquid) that can dissolve other substances (solutes) • Water is a solvent • The collective strength of many hydrogen bonds pulls ions apart and keeps them dissolved

  50. Water’s Solvent Properties • Water dissolves polar molecules • Hydrogen bonds form between water molecules and other polar molecules • Polar molecules dissolved by water are hydrophilic(water-loving) • Nonpolar (hydrophobic) molecules are not dissolved by water

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