申論題

 In an ionic compound, the ions are packed together in a regular arrangement called a lattice. Within the lattice, oppositely charged ions attract one another strongly. The Figure below shows a tiny part of the crystal of sodium chloride. Many trillions of sodium ions and chloride ions would be arranged in this way in the crystal make up the giant ionic structure. Each sodium ion in the lattice is surrounded by six chloride ions, and each chloride ion is surrounded by six sodium ions.

Due to the strong electrostatic forces holding the crystal lattice together, a lot of energy is needed to separate the ions. There ionic compounds have the following properties. 

● They are usually solids at room temperature, with high melting points  

● They are usually hard substances but brittle due to lack of ductility, see figure below.   

● They cannot conduct electricity when solid, because the ions are not free to move it the solid state. However, in the molten state and in aqueous solution, they conduct electricity. 

● They mainly dissolve in water. This is because water molecules are able to bond with both the cations and anions, which breaks up he lattice and keeps the ions apart. 

33a. According to the article of the ionic compound and its properties, finish the cross-words puzzle. [8 marks]