02 Ch02chemistry2005 1
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  • Domains of Study Domain of BioMolecules Domain of Cells Domain of Organisms Domain of Populations Domain of Communities

02 Ch02chemistry2005 1 02 Ch02chemistry2005 1 Presentation Transcript

  • Chapter 2. The Chemical Context of Life 2005-2006
  • Why are we studying chemistry?
    • Biology has chemistry at its foundation
    2005-2006
    • Everything is made of matter
    • Matter is made of atoms
    • Atoms are made of:
      • protons + mass of 1 nucleus
      • neutrons 0 mass of 1 nucleus
      • electrons - mass <<1 orbits
    • Different kinds of atoms = elements
    The Basics 2005-2006
  • The World of Elements 2005-2006
  • Models of atoms 2005-2006 (c)
  • Atomic structure determines behavior
    • The number of protons in an atom determines the element
      • # of protons = atomic number
      • this also tells you # of electrons
    • All atoms of an element have same chemical properties
      • all behave the same
      • properties don’t change
    2005-2006 VIDEO: Atom
  • Discussion Questions
    • What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?
    • An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?
    2005-2006
  • Life requires ~25 chemical elements
    • About 25 elements are essential for life
      • Four elements make up 96% of living matter:
        • • carbon (C) • hydrogen (H)
        • • oxygen (O) • nitrogen (N)
      • Four elements make up most of remaining 4%:
        • • phosphorus (P) • calcium (Ca)
        • • sulfur (S) • potassium (K)
    2005-2006
  • 2005-2006
  • Isotopes
    • Different number of neutrons (heavier)
    • Some are unstable
      • nuclear reactions / decay
    • Split off neutrons &/or protons
      • radioactivity
    • Biological tool
    • Biological hazard
    2005-2006
  • Discussion Question
    • Which drawing depicts the electron configuration of neon ( 20 10 Ne)?
    2005-2006
    • The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium?
    • a. an atom with 20 protons, 21 neutrons, and 20 electrons
    • b. an atom with 21 protons, 20 neutrons, and 21 electrons
    • c. all of the above
    • d. an atom with 21 protons, 21 neutrons, and 21 electrons
    • e. an atom with 20 protons, 20 neutrons, and 18 electrons
    2005-2006
    • Effect of electrons
      • chemical behavior of an atom depends on its electron arrangement
      • depends on the number of electrons in its outermost shell, the valence shell
    2005-2006 Bonding properties How does this atom behave? VIDEO: Electron Arrangement
    • Effect of electrons
      • chemical behavior of an atom depends on number of electrons in its outermost shell
    2005-2006 Bonding properties How does this atom behave? How does this atom behave?
  • Elements & their valence shells 2005-2006
    • Elements in the same row have the same number of shells
  • Discussion Question 2005-2006 Atomic chlorine has an atomic number of 17. It has _____ electrons in its third shell.
  • Elements & their valence shells 2005-2006
    • Elements in the same column have the same valence & similar chemical properties
  • Discussion Question 2005-2006 Based on electron configuration, which of these elements would exhibit chemical behavior most like that of oxygen?
  • Elements & their valence shells 2005-2006
    • Moving from left to right, each element has a sequential addition of electrons (and protons)
  • Chemical reactivity
    • Atoms tend to
      • Complete a partially filled outer (valence) electron shell
      • or
      • Empty a partially filled outer (valence) electron shell
      • This tendency drives chemical reactions
    2005-2006
  • Ionic bonds 2005-2006
  • Ionic bonds
    • Transfer of an electron
    • Forms + & - ions
      • + = cation
      • – = anion
    • Weak bond
    2005-2006
    • example:
      • salt = dissolves easily in water
    Movie: Ionic Bonds
    • Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons?
    • A. The atom would have a double negative charge and be an ion.
    •  
    • B. The atomic number of the atom would remain 29, the mass number would be reduced to 62, and the atom would be an anion.
    • C. The atomic number would remain 29, the mass number would increase to 66, and the atom would be a cation with a -2 charge.
    • D. The atomic number would be reduced to 27, the mass number would remain 64, and the atom would be an anion with a +2 charge.
    • E. The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge.
    2005-2006
  • Covalent bonds
    • Two atoms need an electron
    • Share a pair of electrons
    • Strong bond
      • both atoms holding onto the electrons
    • Forms molecules
    • example:
      • water = takes energy to separate
    2005-2006 VIDEO: Covalent Bond
  • Double covalent bonds
    • Two atoms can share more than one pair of electrons
      • double bonds (2 pairs of electrons)
      • triple bonds (3 pairs of electrons)
    • Very strong bonds
    2005-2006
  • Multiple covalent bonds
    • 1 atom can form covalent bonds with two or more other atoms
      • forms larger molecules
      • ex. carbon
    2005-2006
  • Polar covalent bonds
    • Pair of electrons not shared equally by 2 atoms
    • Water = O + H
    2005-2006
      • oxygen has stronger “ attraction ” for the shared electrons than hydrogen
      • oxygen has higher electronegativity
    Video: Polar vs. Non-Polar
  • Polar covalent bonds
    • 2 hydrogens in the water molecule form an angle
    • Water molecule is polar
      • oxygen end is –
      • hydrogen end is +
    • Leads to many interesting properties of water….
    2005-2006
  • Hydrogen bonds
    • Positive H atom in 1 water molecule is attracted to negative O in another
    • Can occur wherever an -OH exists in a larger molecule
    • Weak bonds
    2005-2006 VIDEO: Hydrogen Bonds
    • What types of bonds are identified in the following illustration of a water molecule interacting with an ammonia molecule? Bonds 1 are polar covalent bonds, bond 2 is a hydrogen bond, and bonds 3 are nonpolar covalent bonds.
    2005-2006
      • Bonds 1 and 3 are polar covalent bonds and bond 2 is a hydrogen bond.
      • Bonds 1 and 3 are polar covalent bonds and bond 2 is an ionic bond.
      • Bonds 1 and 3 are nonpolar covalent bonds and bond 2 is a hydrogen bond.
      • d)Bonds 1 and 3 are polar covalent bonds and bond 2 is a nonpolar covalent bond.
      • e) Bonds 1 and 3 are polar covalent bonds and bond 2 is a nonpolar covalent bond
  • Reductionist view of biology
    • Matter is made of atoms
    • Life requires ~25 chemical elements
    • Atomic structure determines behavior of an element
    • Atoms combine by chemical bonding to form molecules
    • Weak chemical bonds play important roles in chemistry of life
    • A molecule’s biological function is related to its shape
    • Chemical reactions make & break chemical bonds
    2005-2006
  • Any Questions?? 2005-2006