9701 · 4.2
Bonding and structure flashcards
Revision flashcards for Cambridge 9701 Bonding and structure (syllabus 4.2). Flip, recall, then mark a real past-paper question.
Card
What is a giant ionic lattice?
A three-dimensional repeating arrangement of positive and negative ions held together by strong electrostatic forces of attraction. Example: Sodium chloride (NaCl).
Card
Why do ionic compounds have high melting points?
A large amount of thermal energy is required to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the giant lattice structure.
Card
Why can molten or aqueous ionic compounds conduct electricity, but solid ones cannot?
In the solid state, ions are fixed in the lattice and cannot move. When molten or dissolved, the ions are mobile and free to move to carry charge.
Card
Describe the structure and bonding in a metal.
A giant metallic lattice consists of a regular arrangement of positive metal ions surrounded by a 'sea' of delocalised electrons. The bonding is the electrostatic attraction between the positive ions and the delocalised electrons.
Card
Explain why metals are malleable and ductile.
The layers of positive ions can slide over one another without disrupting the metallic bond, as the delocalised electrons are mobile and maintain the attraction. This allows the metal to be hammered into shape (malleable) or drawn into wires (ductile).
Card
What is a giant covalent (macromolecular) structure?
A structure where a very large number of atoms are joined to adjacent atoms by strong covalent bonds, forming a giant, three-dimensional lattice. Examples: Diamond, graphite, silicon(IV) oxide.
Card
Why does graphite conduct electricity, but diamond does not?
In graphite, each carbon atom bonds to three others, leaving one delocalised electron per atom that is free to move between the layers and carry charge. In diamond, all four outer electrons of each carbon atom are used in covalent bonds, so there are no mobile charge carriers.
Card
What is a simple molecular structure?
A structure consisting of discrete (separate) molecules held together by weak intermolecular forces (van der Waals forces, dipole-dipole interactions, or hydrogen bonds). Covalent bonds exist *within* the molecules.
Card
Why do simple molecular substances have low melting and boiling points?
Only a small amount of energy is needed to overcome the weak intermolecular forces between the molecules. The strong covalent bonds *within* the molecules are not broken.
Card
Exam Trap: Is solid iodine ($I_2$) a giant covalent substance?
No. Iodine is a simple molecular substance. It forms a molecular lattice where discrete $I_2$ molecules are held together by weak van der Waals forces. This is why it has a low melting point and sublimes easily.