exam questions mistakes

• The bonding in nitrogen oxide is covalent rather than ionic cause both the nitrogen atom and the oxygen atom have high electronegativities, meaning they have a strong attraction for electrons. In a covalent bond, atoms share electrons, while in an ionic bond, one atom completely transfers electrons to another.
• Why do large differences in electronegativity result in ionic bonds?

  
  

  The more electronegative element will attract the shared pair of electrons to such a large extent than the other that it will amount to transfer of electron resulting in the formation of ions
• permanent dipole-dipole forces of attraction occur in hydrogen chloride as

  • there is a difference in electronegativity due to uneven distribution electrons leading to bond polarity
  • there is an attraction between ∂ + (Cl) on one molecule and ∂ − (H) on another
• Van der Waals' forces exist between all molecules. Explain how these forces arise:

  •  Electron movement in first molecule leads to temporary dipole
  • Induces a dipole in another molecule
  • δ + region on one molecule attracts δ - in neighbouring molecules
• Suggest why methaneselenol (CH3SeH) has a higher boiling point than methanethiol (CH3SH). 

  • methaneselenol is a larger molecule as Se is a bigger atom with more electrons
  • this forms stronger van der Waals forces between the molecules
• to identify if it has hydrogen bonding:

  • F: O: N: ding

  A) deficient

  
• Explain, in terms of electronegativity, why the boiling point of H2S2 is lower than that of H20

  • O is more electronegative than S
  • There is no hydrogen bonding between H2S2 molecules, and only permanent dipole-dipole forces.
• The melting point of silicon is much greater than the melting point of phosphorous. Explain in terms of structure and bonding why this is so.

  •  Si is macromolecular and has covalent bonds between atoms.
  • P is simple molecular and has induced dipole-dipole forces between molecules.
  • Covalent bonds are stronger than induced dipole-dipole forces, so more energy is required to break them
• Explain how the lone pairs of electrons on the oxygen atom influence bond angle in oxygen disulphide

  • lone pair repulsion repel more/ is stronger than bond pair repulsion
  • so the bond angle will reduced/ be lower
• Deduce the type of intermolecular forces in SiF4Explain how this type of intermolecular force arises and why no other type of intermolecular force exists in a sample of SiF4

  • Van der Waals forces
  • (Uneven distribution of electrons in) one molecule induces dipole in neighbouring molecule
  • symmetrical molecule so dipoles cancel
• inorganic ionic compounds always form giant structures
• within silicon dioxide covalent bonds break when it melts
• Kevlar has hydrogen bonding between polymer chains
• electron pairs repel each other equally