Alkenes and their Properties

Question 1

What are the alkenes?

Answer 1

hydrocarbons that have at least one c-c double bond, they are unsaturated.

Question 2

describe the structure of a double bond

Answer 2

• a double bond is made up of a sigma and a pi bond.
  -a sigma bond is formed when two orbitals overlap in a straight line which gives it the highest possible electron density between the two nuclei.
• a pi bond is formed when two p orbitals overlap sideways.
  pi bonds are weaker because the electron density is spread out above and below the nuclei, meaning the electrostatic attraction between the nuclei and the shared pair of electrons is weaker, and so have a relatively low bond enthalpy.

Question 3

describe the reactivity of the alkenes.

Answer 3

-pretty reactive
-has a really high electron density, because there are two pairs of electrons in the bond.
- pi bond sticks out above and below the rest of the molecule, and so the pi bond is likely to be attacked by molecules with a low electron density and can accept a pair of electrons
-low bond enthalpy, because the double bond is so reactive alkenes are good starting points for making organic compounds and for making petrochemicals.

Question 4

describe the double bond rotation

Answer 4

-the carbon atoms in a double bond all lie in the same plane ( they’re planar)
the three bonds repel eachother as much as possible and arrange themselves into a trigonal planar shape.
-the atoms in a carbon carbon double bond cannot rotate around them like they can in a single bond. this is because of the p orbitals having to stay in the same position to overlap.
-double bonds are also fairly rigid and so don’t bend much.