Lecture 2 + 3

Question 1

Difference between sigma and pi bonds

Answer 1

sigma bonds - stronger due to greater overlap
- free rotation, head-on overlap

pi bonds - weaker due to less overlap
- restrict rotation, side-to-side overlap

Question 2

Difference between polar and non-polar molecules

Answer 2

polar - significant difference in electronegativity
- uneven distribution of electron density

non-polar - even distribution of electron density
- no difference in electronegativity

Question 3

Lewis structures of H, C, N, O, P, and S

Answer 3

hydrogen - 1 electron
carbon - 4 electrons
nitrogen - 5 electrons
oxygen - 6 electrons
phosphorous - 5 electrons
sulfur - 6 electrons

Question 4

What is the significance of polarity in water molecules

Answer 4

• hydrogen has partial positive charges
• oxygen has partial negative charge
• negative attracts positive charge
• water can create a 3D network of polar interactions which give water a high boiling point

Question 5

Benzene vs Cyclohexane

Answer 5

cyclohexane - single bonds, aliphatic molecule, flexible, non-planar

benzene - alternating single and double bonds, rigid, planar, non-polar, aromatic (delocalized electrons in pi cloud), stable

Question 6

Chiral vs Achiral

Answer 6

chiral - asymmetrical, non-superimposable mirror images = enantiomers
achiral - symmetrical, superimposable mirror images

Question 7

Delocalized electrons

Answer 7

• electron pairs circulate across the atoms
• resonance
• important property of proteins, electrons can delocalize around a peptide bond