11 topics with brief reviews: definitions, key facts, and class questions.
In the tenth chapter, we analyze the elements of Group VIA, or chalcogens. This section covers the general characteristics of the oxygen subgroup and a detailed study of its main representatives: oxygen itself, ozone, and sulfur. You will learn about key inorganic compounds that play a crucial role in biological systems and medical practice: from familiar water to hydrogen peroxide, sulfur(IV) and (VI) oxides, as well as sulfuric acid.
During seminars and colloquia, instructors most frequently ask about the redox duality of hydrogen peroxide and the chemical properties of peroxides and superoxides. Pay special attention to qualitative reactions for sulfides and sulfates, as well as the properties of hydrogen sulfide—this knowledge is regularly tested during practical laboratory sessions and will certainly appear on exam tickets.
Why cannot oxygen exhibit a valence of IV or VI like sulfur?
The oxygen atom lacks d-orbitals on its outer energy level. Consequently, it has no vacant orbitals with suitable energy for electron unpairing, so its maximum valence is strictly limited to II.
Why is the dioxygen molecule paramagnetic?
The paramagnetism of the O₂ molecule is explained by the presence of two unpaired electrons located in higher-energy antibonding orbitals.
Why doesn't ozone accumulate infinitely in the atmosphere?
Ozone is thermodynamically unstable and constantly breaks down into molecular and atomic oxygen. Its amount remains relatively constant (stationary) due to the balance between decomposition and photochemical synthesis.
What is formed during the hydrolysis of peroxides?
The interaction of peroxides with water produces the corresponding metal hydroxide and hydrogen peroxide ($H_2O_2$).
Why does ice float on the surface of liquid water?
In the temperature range from +4 °C to 0 °C upon cooling, water expands anomalously. Because of this, the solid phase (ice) has a lower density than the liquid phase and is lighter.
Why can hydrogen peroxide decompose explosively?
The pure substance decomposes into water and oxygen very slowly, but the process accelerates sharply and manifold upon contact with metal ions or heterogeneous catalysts.
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