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Life’s Chemical Basis

Explore the fundamental concepts of atoms, isotopes, periodic table, and bonding in this insightful video lesson on life's chemical basis. Learn the significance of electrons, ions, and molecules in shaping the world around us.

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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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