chemical bonding

Question 1

state and explain, with reference to the Valence Shell Electron Pair repulsion theory, the shape of () molecule

Answer 1

• There are () number of electron pairs present in the valence shell of the central atom ().
• To minimise repulsion and maximise stability, the electron geometry of the molecule is ()
• As there are () bond pairs and () lone pairs around the central atom (), the shape of the molecule is ()

() is for me to change according to the context of the question

Question 2

with reference to structure and bonding, explain why does a branched isomer have a lower melting/boiling point than a straight chained isomer. [2]

Answer 2

• while both molecules have simple molecular structures with instantaneous dipole-induced dipole (id-id) attractions between their molecules,
• as (molecule 1) is more spherical than (molecule 2), the surface area of contact between the (molecule 2) molecules decreases, causing the id-id attractions to become less extensive,
• hence, less energy is required to overcome the less extensive id-id attractions between (molecule 2) molecules, thus, boiling point decreases

Question 3

with reference to structure and bonding, explain why (polar molecule) has a higher melting/boiling point than (non-polar molecule), when they have comparable Mr

Answer 3

• both (polar molecule) and (non-polar molecule) have simple molecular structures
• however, more energy is required to overcome the stronger permanent dipole-permanent dipole (pd-pd) attractions between the polar (polar molecules) molecules,
• compared to the weaker instantaneous dipole-induced dipole (id-id) attractions between the non-polar (non-polar molecules) molecules
• hence, (non-polar molecule) has a higher melting/boiling point than the (non-polar molecule)

Question 4

with reference to structure and bonding, explain why (molecule 1) has the highest melting/boiling point out of the 4 molecules.

Answer 4

• all the molecules have simple molecular structures
• as Mr of (molecule 1) > Mr of (molecule 2) > Mr of (moelcule 3) > Mr of (molecule 4), the size of electron cloud of (molecule 1) > electron cloud of (molecule 2) > electron cloud of (moelcule 3) > electron cloud of (molecule 4)
• hence, the extent of polarisation of the electron cloud (molecule 1) > extent of polarisation of the electron cloud (molecule 2) > extent of polarisation of the electron cloud (molecule 3) > extent of polarisation of the electron cloud (molecule 4), therefore, (molecule 1) has the strongest and most extensive instantaneous dipole-induced dipole [id-id] attractions
• thus, the most energy is required to overcome the id-id attractions between (molecule 1), hence, boiling point of molecule 1 is the highest amongst all the molecules