Chapter 18: The Representative Elements

What special property of the noble gases makes them unreactive? The boiling points and melting points of the noble gases increase steadily from Heto XeExplain.

Although He is the second most abundant element in the universe, it is very rare on earth. Why?

The noble gases were among the latest elements discovered; Mendeleev did not predict their existence when he published his first periodic table. Explain. In chemistry textbooks written before 1962, noble gases were referred to as inert gases. Why do we no longer use the term inert gases?

Argon gas is inert, so it poses no serious health risks. However, if significant amounts of radon are inhaled into the lungs, lung cancer is a possible result. Explain the health risk differences between argon gas and radon gas.

There is evidence that radon reacts with fluorine to form compounds similar to those formed by xenon and fluorine. Predict the formulas of these ${\mathbf{R}}_{\mathbf{n}}{\mathbf{F}}_{\mathbf{x}}$ compounds.

What will be the atomic number of the next alkali metal to be discovered? How would you expect the physical properties of the next alkali metal to compare with the properties of the other alkali metals summarized in Table?

Using the element phosphorus as an example, write equations for the process in which the energy change corresponds to the ionisation energy and to the electron affinity.

Atomic size seems to play an important role in explaining some differences between the first element in a group and the subsequent group elements. Explain.

What are the two most abundant elements by mass in the earth’s crust, oceans, and atmosphere? Does this make sense? Why? What are the four most abundant elements by mass in the human body? Does this make sense? Why?

In most compounds, the solid phase is denser than the liquid phase. Why isn’t this true for water?