Explain why solder is harder than pure tin. Complete the sentences. Use Figure 4.\n\nIn solder the layers are distorted.\nThis is because the atoms of tin and lead have different ______.\nTherefore the layers cannot easily ______.

In a pure metal like tin, the atoms are all the same size and are arranged in regular, orderly layers. These layers can slide over each other easily, which makes the metal relatively soft and malleable.\n\nIn an alloy like solder, there are atoms of different elements (tin and lead). These atoms have different sizes. The presence of different-sized atoms disrupts the regular layered structure, making it distorted. This distortion means the layers can no longer slide over each other easily. As a result, a greater force is required to change the shape of the alloy, making it harder and stronger than the pure metal.