HPQ:Chemistry:Post 16:Bonding and Structure:Keith Guy

Question

Which two of these statements is correct when melting ice and silicon dioxide (a giant covalent structure)

A. Strong covalent bonds break within the silicon dioxide
B. Weak intermolecular forces break between water molecules
C. Weak intermolecular forces break between silicon dioxide molecules
D. Strong covalent bonds break within water molecules

Answer

A and B

It is a common misconception that covalent bonds between atoms within molecules break on melting and boiling. Students should understand that ice, water and steam all consist of molecules of H₂O. In addition the students should become familiar with four substances, (silicon, silicon dioxide, graphite and diamond), which form giant crystalline structures in which covalent bonds between atoms do break on melting and boiling.