Question

For each of the following groups, which metal would you expect to have the highest melting point: (a) gold, rhenium, or cesium; (b) rubidium, molybdenum, or indium; (c) ruthenium, strontium, or cadmium?

Short answer

The metals with the highest melting points in each group are (a) rhenium, (b) molybdenum, and (c) ruthenium. This is due to their positions in the periodic table, with transition metals generally having stronger metallic bonds and higher melting points compared to alkali and alkaline earth metals.

Step-by-step solution

(a) Gold, Rhenium, or Cesium

In this group, gold (Au) and rhenium (Re) are transition metals, while cesium (Cs) is an alkali metal. Since transition metals tend to have higher melting points due to stronger metallic bonds, we can eliminate cesium. Between gold and rhenium, we can look at their positions in the periodic table. Rhenium is closer to the center and lower down in the table than gold, which indicates that its metallic bonds are stronger. Therefore, rhenium is expected to have the highest melting point in this group.

(b) Rubidium, Molybdenum, or Indium

In this group, molybdenum (Mo) is a transition metal, while rubidium (Rb) is an alkali metal and indium (In) is part of the p-block. As we mentioned earlier, transition metals generally have higher melting points. Therefore, we can first eliminate rubidium. Comparing molybdenum and indium, molybdenum is a transition metal, placing it in a better position for stronger metallic bonds. Therefore, molybdenum is expected to have the highest melting point in this group.

(c) Ruthenium, Strontium, or Cadmium

In this group, ruthenium (Ru) and cadmium (Cd) are transition metals, while strontium (Sr) is an alkaline earth metal. We can eliminate strontium for being an alkaline earth metal. Comparing ruthenium and cadmium, ruthenium is closer to the center and lower down in the periodic table, indicating stronger metallic bonds in its crystal lattice. Therefore, ruthenium is expected to have the highest melting point in this group.