Bio1151 Chapter 2 The Chemical Context of Life
  1. Living organisms are subject to basic laws of physics and            . One example is the use of formic acid by ants to maintain "devil’s gardens".

      The rainforest ant Myrmelachista schumanni nests in stands of Duroia trees called "devil's gardens". The ants kill all trees except its host plant by injecting formic acid into competing trees such as Cedrela. Continue
     
     
     
     
  2. Matter consists of chemical           in pure form and in combinations called            .

      Electronshell diagrams of the first 18 elements in the periodic table. An element is a substance that cannot be broken down to other substances by chemical means. The first electron shell can contain up to 2 electrons; the 2nd and 3rd shells can contain up to 8 electrons.
     
     
     
     
  3. Four elements make up 96% of living matter:         (C),           (H),         (O), and           (N).
     
     
     
     
  4. Each element is made of a single kind of       . An atom is made of           ,          , and            .

      In a helium atom, the nucleus consists of 2 neutrons which have no electrical charge, and 2 protons which are positively charged. Two electrons, which are negatively charged, move around the nucleus. The atomic number of an element is the number of protons in the nucleus. The mass number (atomic mass) is the sum of protons plus neutrons.
     
     
     
     
  5. Electrons occupy different         with different energy         . The outermost, or          , shell contains          electrons.

      Energy levels of an atom's electrons. Electrons exist only at fixed levels of potential energy, which are also called electron shells. The outermost shell is called the valence shell, and contains valence electrons, and most chemical reactions involve those electrons, since atoms are most stable with complete valence shells. .
     
     
     
     
  6. A           bond is the          of a pair of          electrons between different atoms of a           . These bonds are strong and stable.

      Covalent Bond. In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton. in the other nucleus. The two electrons become shared in a covalent bond, forming an H[2] molecule.
     
     
     
     
  7. A         covalent bond is the sharing of two pairs of valence electrons.

      Single and double covalent bonds. Hydrogen (H[2]). Two hydrogen atoms can form a single bond. Oxygen (O[2]). Two oxygen atoms share two pairs of electrons to form a double bond. Water (H[2]O). Two hydrogen atoms and one oxygen atom are joined by single covalent bonds to produce a molecule of water. Methane (CH[4]). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane.
    • Q: What kind of bonds form between these hydrogen atoms and carbon?
      + A: Single covalent bond.
     
     
     
     
  8. Electronegativity is the attraction of an atom for            . In a        covalent bond the atoms have different electronegativities and share the electrons            .

      A water molecule is polar because oxygen is more electronegative than hydrogen, so there is a partial negative charge on the oxygen and a partial positive charge on the hydrogens. The unequal sharing of electrons results in a polar covalent bonds.
     
     
     
     
  9. In an        bond one atom strips            away from other atoms, creating          atoms called       .

     
     
     
     
  10. Ionic compounds are often called        , which may form           .

      A sodium chloride crystal (salt). The sodium ions (Na^+) and chloride ions (Cl^-) are held together by ionic bonds. The formula NaCl indicates that the ratio of Na^+ to Cl^- is 1:1.
     
     
     
     
  11. Electronegativity can result in weak chemical bonds.
       
       
       
       
    • A           bond forms from the attraction of charged regions of        molecules.

        A hydrogen bond results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia.
       
       
       
       
    •                interactions form when transiently charged regions of molecules attract each other.
Bio1151 Chapter 3 Water and the Fitness of the Environment
  1.        is the biological medium here on Earth.



     
     
     
     
  2. Water is a        molecule, and its numerous           bonds result in unique properties.

     
     
     
     
    •           among water molecules and           between water and other molecules.



       
       
       
       
    • High           heat            nearby air and ground temperatures and leads to              cooling of wet surfaces.



       
       
       
       
    • Solid water is less        than liquid water and floats, allowing life under frozen surfaces.

       
       
       
       
    • Water is a versatile          and can dissolve              substances which are either ionic or polar.



       
       
       
       
      • Substances too large to dissolve in water can form a          , such as in the          of a cell.


     
     
     
     
  3. Water can dissociate into H+ (hydrogen) and OH- (hydroxide)       .

     
     
     
     
    • The concentration of these ions is measured on the     scale.

       
       
       
       
    • An       has a high concentration of H+ ions, while a       has a low concentration.
       
       
       
       
    •       precipitation is caused primarily by the mixing of water vapor and         and           oxides produced by the combustion of         fuels.




      Fossil fuels (coal, petroleum, natural gas) are formed from buried remains of dead organisms when compressed in sediment over time. Humans have dug up these carbon fuels to burn as energy sources, releasing excess carbon into the atmosphere.