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Life’s Chemical Basis

Life’s Chemical Basis. Chapter 2. 2.1 Start With Atoms. Atoms Fundamental building blocks of matter Nucleus Positively charged protons Uncharged neutrons (except for hydrogen) Electrons move around the nucleus Negatively charged. Atoms. nucleus. electron. Fig. 2.3, p. 22.

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Life’s Chemical Basis

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  1. Life’s Chemical Basis Chapter 2

  2. 2.1 Start With Atoms • Atoms • Fundamental building blocks of matter • Nucleus • Positively charged protons • Uncharged neutrons (except for hydrogen) • Electrons move around the nucleus • Negatively charged

  3. Atoms

  4. nucleus electron Fig. 2.3, p. 22

  5. Fig. 2.3, p. 22

  6. Fig. 2.3, p. 22

  7. Elements • Element • A pure substance consisting of atoms with the same number of protons (atomic number) • Isotopes • Atoms of the same element that differ in number of neutrons (atomic weight)

  8. Periodic Table of Elements

  9. Abundance of Elements

  10. Seawater Human Hydrogen 66.0% Oxygen 33.0 Carbon 0.1 Nitrogen 0.1 Phosphorus 0.1 Calcium 0.1 Sodium 0.3 Potassium 0.1 Chlorine 0.3 Hydrogen 62.0% Oxygen 24.0 Carbon 12.0 Nitrogen 1.2 Phosphorus 0.2 Calcium 0.2 Sodium 0.1 Potassium 0.1 Chlorine  0.1 Earth Hydrogen 3.1% Oxygen 60.0 Carbon 0.3 Nitrogen 0.1 Phosphorus 0.1 Calcium 2.6 Sodium 0.1 Potassium 0.8 Chlorine 0.1 Fig. 2.2, p. 21

  11. Animation: Shell models of common elements CLICK HERE TO PLAY

  12. Animation: Chemical bookkeeping CLICK HERE TO PLAY

  13. 2.2 Putting Radioisotopes to Use • Radioisotopes are radioactive isotopes • They are not stable • Emit particles and energy as they decay spontaneously into other elements

  14. Radioactive Decay • A radioisotope decays at a constant rate into the same products • Example:14C → 14N • Tracer • Molecule with a detectable substance attached • PET scans

  15. A PET Scan

  16. portion of the patient’s body being scanned Fig. 2.5, p. 23

  17. portion of the patient’s body being scanned detector ring inside the PET scanner Fig. 2.5, p. 23

  18. The ring intercepts emissions from the labeled molecules Fig. 2.5, p. 23

  19. Fig. 2.5, p. 23

  20. Animation: PET scan CLICK HERE TO PLAY

  21. Key Concepts:ATOMS AND ELEMENTS • Atoms are fundamental units of all matter • Protons, electrons, and neutrons are their building blocks • Elements are pure substances consisting of atoms that have the same number of protons • Isotopes are atoms of the same element that have different numbers of neutrons

  22. 2.3 Why Electrons Matter • Electrons occupy orbitals (volumes of space) around the nucleus • Up to two electrons occupy each orbital • Shell model represents orbital energy levels as successively larger circles, or shells • Used to view an atom’s electron structure

  23. Shell Models

  24. Electron Interactions • Atoms with unpaired electrons in their outermost shell tend to interact with other atoms • They donate, accept, or share electrons to eliminate vacancies vacancy no vacancy

  25. electron sodium 11p+ , 11e- chlorine 17p+ , 17e- argon 18p+, 18e- carbon 6p+ , 6e- oxygen 8p+ , 8e- neon 10p+, 10e- hydrogen 1p+ , 1e- helium 2p+ , 2e- Fig. 2.6, p. 24

  26. Electrical Charge • An atom with equal numbers of protons and electrons has no net charge • Ions (positive or negative) • Atoms that have gained or lost electrons • Electronegativity • Measure of how strongly an atom attracts electrons from other atoms

  27. Ion Formation

  28. Sodium atom 11p+ 11e- Chlorine atom 17p+ 17e- no net charge no net charge electron loss electron gain Chlorine atom 17p+ 18e- Sodium ion 11p+ 10e- net negative charge net positive charge Fig. 2.7, p. 25

  29. Sodium atom 11p+ 11e- Chlorine atom 17p+ 17e- no net charge no net charge electron loss electron gain Chlorine atom 17p+ 18e- Sodium ion 11p+ 10e- net negative charge net positive charge Stepped Art Fig. 2-7, p. 25

  30. Molecules and Mixtures • Chemical bond • Attractive force that unites atoms into a molecule • Compounds • Molecules consisting of two or more elements • Mixture • Substances intermingle but don’t bond

  31. Representing Molecules

  32. Key Concepts:WHY ELECTRONS MATTER • Whether one atom will bond with others depends on the number and arrangement of its electrons

  33. Animation: Electron arrangements in atoms CLICK HERE TO PLAY

  34. Animation: The shell model of electron distribution CLICK HERE TO PLAY

  35. Animation: How atoms bond CLICK HERE TO PLAY

  36. 2.4 What Happens When Atoms Interact? • Common interactions in biological molecules: • Ionic bond • Covalent bond • Hydrogen bond

  37. Ionic Bonds • Strong association between a positive ion and a negative ion (attraction of opposite charges)

  38. a A crystal of table salt is a cubic lattice of many sodium ions and chloride ions. b The mutual attraction of opposite charges holds the two kinds of ions together closely in the lattice. Sodium ion Chloride ion Fig. 2.8, p. 23

  39. Animation: Ionic bonding CLICK HERE TO PLAY

  40. Covalent Bonds • Two atoms share a pair of electrons • Nonpolar covalent bond • Atoms share electrons equally • Polar covalent bond • Electrons are shared unequally • One end slightly negative, other slightly positive • Polar molecule has a separation of charge

  41. Covalent Bonds

  42. Molecular hydrogen (H—H) Two hydrogen atoms, each with one proton, share two electrons in a single nonpolar covalent bond. Molecular oxygen (O—O) Two oxygen atoms, each with eight protons, share four electrons in a nonpolar double covalent bond.0 Water molecule (H—O—H) Two hydrogen atoms each share an electron with an oxygen atom in two polar covalent bonds. The oxygen exerts a greater pull on the shared electrons, so it has a slight negative charge. Each hydrogen has a slight positive charge. Fig. 2.9, p. 27

  43. Hydrogen Bonds • Form between a hydrogen atom and an electronegative atom • Each with separate polar covalent bonds • Are not chemical bonds • Do not make atoms into molecules • Individually weak • Collectively stabilize structures of large molecules

  44. Hydrogen Bonds

  45. hydrogen bond water molecule ammonia molecule a Two molecules interacting in one hydrogen (H) bond. b Numerous H bonds ( white dots) hold the two coiled-up strands of a DNA molecule together. Each H bond is weak, but collectively these bonds stabilize DNA’s large structure. Fig. 2.10, p. 27

  46. Animation: Examples of hydrogen bonds CLICK HERE TO PLAY

  47. 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

  48. 2.5 Water Molecules • Water molecules are polar • Form hydrogen bonds with other polar molecules • Hydrophilic substances (water-loving) • Hydrophobic substances (water-dreading)

  49. slight negative charge on the oxygen atom - O The positive and negative charges balance each other; overall, the molecule carries no charge. H H + + slight positive charge on the hydrogen atoms Fig. 2.11, p. 28

  50. Animation: Structure of water CLICK HERE TO PLAY

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