problems with basic chem?

Question

Could someone help me out with these baic che problems? I can't find the answers in my book:

1. Contrast alkanes and alkenes, and give an example of each.
2. Explain the similarities between alcohol molecules and water molecules.
3. Explain how glucose and starch are related.
4. Explain why carbon can never form more than a total of four bonds.
5. Explain how the bases that form DNA make pairs.

Thanks to anyone that helps

Answer 1

1.) Alkanes have all single bonds. Alkenes have at least 1 double bond. Alkanes are considered saturated (it has the maximum amount of Hydrogen possible), Alkenes are unsaturated.

Ex: ethane (alkane): C2H6 has a single bond between carbons. Ethene (or Ethylene) (alkene): C2H4 has a double bond between carbons.

2. Alcohol has a hydrocarbon attached to an OH (hydroxyl) group. Water has a hydrogen attached to the OH. Both are polar, have similar boiling points compared to other hydrocarbons, and react similarly to acids and bases.

3.) Glucose is a simple sugar. Starch is a complex carbohydrate and complex sugar (polysaccharide), and is made up of polymers of glucose (many glucose molecules).

4.) Carbon has 4 valence electrons available in outer electron orbits. The other electrions require too much energy to bond with. A chemical bond requires that electrons be shared between 2 atoms, thus, Carbon must share at least 1 electron per bond formed. 4 available electrons mean that there are 4 possible bonds.

5.) Ringed hydrocarbons (adenine (A), thymine (T), guanine (G), cytosine (C), uracil (U) are all ringed hydrocarbons) sometimes form shorter bonds that allow for what is called "electron delocalization", which means that there are extra electrons shared between the number of bonds.

A good example is Benzene (C6H6), where instead of having 3 double bonds and 3 single bonds, there are 6 equal length bonds that are somewhat between double and single bonds, and the extra 3 electrons are shared among all 6 carbon atoms.

Those delocalized electrons can also form a weak bond with another molecules. In DNA and RNA, the delocalized electrons are shared among Carbon, Nitrogen, and Oxygen atoms, and can form a weak bond with the opposing molecule in the helix.

Because this bond is very weak, it allows DNA to stay together, but also be easily cut in half by enzymes so that it can be copied during mitosis.