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Water and Molecular Bonds -Exam 1

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Termini in questo insieme (20)

  • What type of bond shares electrons equally between atoms?
    Nonpolar covalent bonds share electrons equally, such as in C-C or C-H bonds.
  • What makes a covalent bond polar?
    A polar covalent bond shares electrons unequally due to differences in electronegativity, e.g., O-H or C-O bonds.
  • Why is water (H2O) a polar molecule?
    Water is polar because it has polar covalent bonds and an asymmetrical (bent) shape, causing partial charges.
  • What is electronegativity and how does it relate to water's polarity?
    Electronegativity is an atom's ability to attract electrons; oxygen (3.44) is more electronegative than hydrogen (2.1), pulling electrons closer and creating polarity.
  • What are the partial charges on a water molecule?
    Oxygen has a partial negative charge (δ-) and hydrogens have partial positive charges (δ+) due to unequal electron sharing.
  • What is the molecular geometry of water?
    Water has a bent molecular shape with a bond angle of about 104.4°, due to two lone pairs on oxygen.
  • How do hydrogen bonds form between water molecules?
    Hydrogen bonds form between the partially positive hydrogen of one water molecule and the partially negative oxygen of another.
  • Are hydrogen bonds covalent bonds? Explain.
    No, hydrogen bonds are noncovalent interactions involving attraction between partial charges, not electron sharing.
  • Why are hydrogen bonds important in biology?
    They stabilize structures like DNA double helix and protein folding, and give water its unique properties.
  • What are emergent properties of water due to hydrogen bonding?
    Properties include cohesion, adhesion, high specific heat, ice floating, and solvent abilities.
  • What is cohesion and adhesion in water?
    Cohesion is water molecules sticking to each other; adhesion is water molecules sticking to other polar surfaces.
  • How does water moderate temperature changes?
    Water's high specific heat means it absorbs/releases heat slowly, stabilizing temperatures.
  • Why does ice float on liquid water?
    Ice forms a less dense crystal lattice due to stable hydrogen bonds, making it float.
  • What does hydrophilic mean?
    Hydrophilic molecules are polar and interact well with water, dissolving easily.
  • What does hydrophobic mean?
    Hydrophobic molecules are nonpolar and do not dissolve in water, avoiding hydrogen bonding.
  • How does salt (NaCl) dissolve in water?
    Water molecules surround ions; oxygen attracts Na+ and hydrogen attracts Cl-, separating the ions.
  • What is pH a measure of?
    pH measures the concentration of hydrogen ions [H+] in a solution.
  • What is the pH of pure water and why?
    Pure water has a neutral pH of 7 because [H+] equals [OH-].
  • How does the pH scale work?
    The pH scale is logarithmic; each unit change represents a tenfold change in [H+].
  • What is the role of buffers in biological systems?
    Buffers resist changes in pH by accepting or donating H+ ions to maintain stable conditions.