Alkenes

Question 1

List the main properties of Alkenes:

Answer 1

• Unsaturated (= bond) as they can make more bonds with extra atoms in addition reactions.
• General Formula: CnH2n
• All contain at least one double bond (=), may have more.

Question 2

What is the symbol for a sigma bond?

Answer 2

σ

Question 3

How is a sigma bond formed?

Answer 3

• Formed when two S-Orbitals overlap in straight lines. This gives the highest possible electron density between two nuclei.
• Single covalent bond.
• Forms between C-C and C-H bonds in alkanes.

Question 4

What is the symbol for Pi bonds?

Answer 4

π

Question 5

How are Pi bonds formed?

Answer 5

• Formed by sideways overlap of two adjacent p-orbitals. Two parts: One above and one below the molecular axis due to dumb-bell shape.
• Occurs in Alkenes.

Question 6

Are Pi bonds or Sigma bonds stronger?

Answer 6

Sigma bonds are stronger as their high electron density leads to a very strong electrostatic attraction between the nucleus and shared electron pairs.

They have a high bond enthalpy and are the strongest type of covalent bond.

Pi bonds are weaker since their electron density is spread out much more both above and below the nucleus.

Question 7

What is the arrangement of the atoms in an alkene?

Answer 7

In a C=C bond (and the atoms attached to it) , they lie in the same plane and have a Trigonal Planear (bond angle 120°) arrangement.

Some alkanes (like ethene) are completely planear, but larger ones may only have the C=C element planear.