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Water and Molecular Bonds in General Biology

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  • 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?
    Polar covalent bonds share 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 oxygen is more electronegative than hydrogen, causing electrons to spend more time near oxygen, creating partial charges.
  • What is the shape and bond angle of a water molecule?
    Water has a bent molecular shape with a bond angle of about \(104.4^\circ\) due to lone pairs on oxygen.
  • What is electronegativity and how does it relate to bond polarity?
    Electronegativity is an atom's ability to attract electrons; differences cause unequal sharing, leading to polar bonds.
  • What are hydrogen bonds?
    Hydrogen bonds are weak attractions between a partially positive hydrogen and a partially negative atom like oxygen or nitrogen.
  • How strong are hydrogen bonds compared to covalent bonds?
    Hydrogen bonds are about 5% as strong as covalent bonds but are important due to their cumulative effects.
  • What emergent properties of water arise from hydrogen bonding?
    Properties include cohesion, adhesion, high specific heat, ice floating, and water as a good solvent for polar molecules.
  • Why does ice float on water?
    Ice is less dense because stable hydrogen bonds form a crystal lattice that spaces molecules apart.
  • What does hydrophilic mean?
    Hydrophilic molecules are polar and interact well with water, dissolving easily.
  • What does hydrophobic mean?
    Hydrophobic molecules are nonpolar, do not form hydrogen bonds, and do not dissolve in water.
  • How does water dissolve ionic compounds like salt (NaCl)?
    Water molecules surround ions, with oxygen attracting Na+ and hydrogen attracting Cl-, separating the ions.
  • What is the pH scale a measure of?
    pH measures the concentration of hydrogen ions \([H^+]\) in a solution on a logarithmic scale.
  • What is the pH of pure water and why?
    Pure water has a neutral pH of 7 because \([H^+] = [OH^-]\).
  • How does a change of one pH unit affect hydrogen ion concentration?
    A one-unit change in pH represents a tenfold change in \([H^+]\) concentration.
  • What is the role of buffers in biological systems?
    Buffers resist changes in pH by accepting or donating hydrogen ions to maintain stable conditions.
  • What is the difference between polar and nonpolar molecules in terms of symmetry?
    Polar molecules are asymmetrical with uneven charge distribution; nonpolar molecules are symmetrical with even charge distribution.
  • How do hydrogen bonds contribute to DNA structure?
    Hydrogen bonds hold complementary base pairs together, stabilizing the DNA double helix.
  • What is the difference between polar covalent bonds and hydrogen bonds?
    Polar covalent bonds share electrons unequally within a molecule; hydrogen bonds are weak attractions between molecules.
  • Why is the shape of a molecule important for its polarity?
    Molecular shape determines if polar bonds create an overall dipole; asymmetry leads to polarity.