1.1.  Figure 1 shows two different models, X and Y, that represent an ionic structure.

                                                           X                                                                   Y

Figure 1

What do the different colour spheres represent in the models?

1.2. Evaluate model X.

You should mention the advantages and limitations.

1.3. Table 1 shows the melting points for two different ionic substances.

 Table 1

Suggest a reason for the difference in melting points.

1.4. The melting point of sodium fluoride (NaF) is 992°C.

Predict if the melting point of rubidium fluoride (RbF) is higher or lower.

Give a reason for your answer.