Today is 8 March 2008 -- Why is carbon able to enter into chemical reactions with so many other elements? And other questions.

Carbon has four electrons in its outer shell.  It needs to gain four to complete the shell, or to lose four so the underlying shell is seen as complete.  The energy to remove the four electrons is enormous so that doesn't happen (on this planet, normally, anyhow).  Gaining electrons would give it a high negative charge (four electrons, remember) and the charge imbalance between the four positive protons and four more electrons results in a very unstable ion.  So THAT doesn't happen.  Instead, the carbon shares electrons covalently with other atoms.  If it is in a salt like calcium carbonate, CaCO3, it is still covalently bound to the oxygen.    Further, since there are four bonds to be formed, the number of combinations are large.  Carbon can form single, double and triple bonds.  When it bonds to other carbon atoms, it forms a crystal or lattice as in diamond or Buckyballs.

2.  Why is water a liquid under normal atmospheric conditions?

Because although the hydrogen atoms in a molecule of water are covalently bound to an oxygen atom, they are not completely neutral in the sense that they are able to be attracted to the oxygen of an adjacent water molecule.  This "hydrogen bonding" is strong enough to keep the molecules from drifting apart under normal conditions.  In the atmosphere, when the air pressure is low, the molecules have enough energy to break free and form water vapor, or if heated, they gain enough energy to overcome the strength of the hydrogen bonds.  If our plant had a lower atmospheric pressure, or was hotter, there would be more water in the vapor phase and less in the liquid.

3.  Write and balance the decomposition of calcium carbonate:

This was discussed over and over in class.  I'm really disappointed that more of you did not write the correct answer.  When calcium carbonate is heated, it forms carbon dioxide and calcium oxide.  

CaCO3 --> CaO + CO2 .

4.  Write and balance the following reaction:  Complete oxidation of sugar (C6H12O6) in the body to produce CO2 and H2O.  Again, we went over this in class.

C6H12O6 + 6O2 --> 6CO2 + 6H2O

5.  Show the Lewis dot diagram for CaCl2

You know that this means one calcium and two chlorine.  You should know that chlorine has 7 electrons in its outer orbital and wants to gain one.  You also should know that calcium has two electrons in its outer orbital and can lose them in forming a bond.  Draw the dot diagram with chlorine on either side of the calcium like this:  Cl : Ca : Cl   Then, add two dots over each Cl, two under them and two between each of the atoms.  Now, check:  There are 16 electrons in all, seven from each of two chlorine atoms and two from the one calcium atom.  That adds up to 16 electrons.  Two between the Cl and the Ca (on each side) uses 4, leaving 12.  Since we need the same number of electrons for each of two Cl, divide 12 electrons by 2 atoms and get 6 electrons for each Cl.  Arrange the dots around the Cl.  Then, stand back and admire your artwook.