Module 6 part 1

• what shape is the benzene molecule, what is it's bond angle?

  it has a planar shape, with a bond angle of 120 degrees.
• what is an arene?

  an aromatic hydrocarbon
• what is an aromatic compound?

  A compound that has one or more benzene rings
• what are the three general pieces of evidence that the electrons in a benzene ring are delocalised?

  The bond lengths are equal

  The enthalpy of hydrogenation is low

  The reactions of benzene
• why does the delocalisation of Pi electrons in a benzene ring increase the stability of it?

  The electrons are equally spread across the entire structure- thus decreasing the electron density compared to a double bond
• why is a benzene ring very stable?

  Due to it's delocalised structure
• what three things about the reactions of benzenes prove it's delocalised structure?

  It doesnt undergo addition reactions as easily as alkenes do

  It more easily undergoes electrophillic substitution reactions

  It is generally less reactive than alkenes
• how is a sigma bond formed?

  Sigma bonds are formed by direcr overlaps of atomic orbitals which result in a shared pair of electrons that are located between the two atoms
• How are pi bonds formed?

  Pi bonds are formed by the sideways overlap of p orbitals, this results in a shared pair of electrons located above and below the plane of carbon atoms.
• what 3 observations about the reactions of benzene show it's delocalised nature?

  Benzene doesn't go through addition reactions as easily as alkenes

  Benzene more easily undergoes electrophilic substitution reactions

  benzene is generally less reactive than alkenes
• by how many kilojules of energy is benzene stronger than kekule's structure?

  152 kilojules per mole ^-1
• why do the equal bond lengths prove that the structure of benzene cannot contain alternating single and double bonds as kekule originally proposed?

  The bond lengths would alternate
• How do the C-C bonds in Benzene compare to a single bond (C-C) and double bonds (C=C)?

  The single bonds in benzene are shorter than regular single bonds but longer than a double bond
• how is a sigma bond formed?

  Sigma bonds are formed by direct end to end overlap of atomic orbitals which result in a shared pare of electrons between the two atoms
• How are pi bonds formed?

  They are formed by the sideways overlap of p orbitals, resulting in a shared pair of electrons located above and below the plane of carbon atoms
• Out of sigma and Pi bonds, which is stronger and why?

  Sigma bonds are stronger due to the direct overlap.
• in ethene, how many sigma and pi bonds are there?

  1 sigma and 1 pi
• Why is a double bond stronger than a single bond but not twice as strong as a single bond?

  A double bond consists of one sigma and one pi bond. Sigma bonds are stronger than pi bonds so a double bond isnt as strong as two sigma bonds
• why is the pi bond in ethene described as localised?

  Because it is between 2 carbon atoms#