Topic 3 (Bondings and Polarization)

Draw electron density map for:

Non-polar covalent bonds (like H₂, Cl₂, O₂)

Polar covalent bonds ( like HCL)

ionic compounds/bonds ( like NaCl)

State what is meant by a dative covalent bond. (2 marks)

- A covalent bond where both electrons in the shared pair are

- provided by one atom

NOTE:
In NH4+ both electrons are provided by N

the arrow → means dative covalent bond

Nitrogen has no vacant d orbitals, so it cannot expand its octet beyond eight electrons. Therefore, it cannot form five covalent bonds (NCl₅).

Explain why aluminium chloride in the solid state has significant covalent character

[2marks]

- Al³⁺ is small and highly charged

- so it strongly polarises the (electron cloud of) Cl⁻, thus giving AlCl₃ significant covalent character.

• they are joined by dative covalent bonds
  
  (draw the diagram in pic)

Complete the diagram to show dative covalent bonds.

State why N cannot form pentachlorides like Sb

• arrows from Cl → Sb because Cl has lone pairs so its contributing/providing both electrons
  

• In N(1s2 2s2 2p3) no 2d orbitals exist (so it cannot expand it's octet)
  
  

Suggest how the electrons in outer shell of iodine rearrange to form ICl3

[2marks]

- One electron from the 5p orbital is promoted (to an empty 5d orbital)

- iodine can form 3 covalent bonds and 2 lone pairs

Since CaCl2 is an ionic compound, add + & - charges

Explain why gaseous beryllium chloride and solid calcium chloride have different types of bonding.

[3 marks]

check this:

- Be2+ ion is smaller

- so it has more polarizing power

- thus BeCl2 is more covalent and CaCl2 is more ionic