Question

Write the chemical formula for each of the following compounds, and indicate the oxidation state of the group \(6 \mathrm{~A}\) element in each: (a) sulfur tetrachloride, (b) selenium trioxide, (c) sodium thiosulfate, (d) hydrogen sulfide, (e) sulfuric acid, \((\mathbf{f})\) sulfur dioxide, \((\mathrm{g})\) mercury telluride.

Short answer

(a) Sulfur tetrachloride: \(\text{S}\text{Cl}_4\), oxidation state of sulfur is +4. (b) Selenium trioxide: \(\text{Se}{\text{O}}_3\), oxidation state of selenium is +6. (c) Sodium thiosulfate: \(\text{Na}_2\text{S}_2\text{O}_3\), oxidation state of sulfur is +2. (d) Hydrogen sulfide: \(\text{H}_2\text{S}\), oxidation state of sulfur is -2. (e) Sulfuric acid: \(\text{H}_2\text{SO}_4\), oxidation state of sulfur is +6. (f) Sulfur dioxide: \(\text{SO}_2\), oxidation state of sulfur is +4. (g) Mercury telluride: \(\text{HgTe}\), oxidation state of tellurium is -2.

Step-by-step solution

(a) Sulfur tetrachloride

Sulfur tetrachloride contains one sulfur atom (S) and four chlorine atoms (Cl). The chemical formula for this compound is \(\text{S}\text{Cl}_4\). Now, to find the oxidation state of sulfur: Each chlorine atom has an oxidation state of -1, so four chlorine atoms will have a total oxidation state of -4. As the sulfur atom needs to balance the oxidation states, it will have an oxidation state of +4. Hence, the oxidation state of sulfur in \(\text{S}\text{Cl}_4\) is +4.

(b) Selenium trioxide

Selenium trioxide contains one selenium atom (Se) and three oxygen atoms (O). The chemical formula for this compound is \(\text{Se}{\text{O}}_3\). Now, to find the oxidation state of selenium: Each oxygen atom has an oxidation state of -2, so three oxygen atoms will have a total oxidation state of -6. As the selenium atom needs to balance the oxidation state, it will have an oxidation state of +6. Hence, the oxidation state of selenium in \(\text{Se}{\text{O}}_3\) is +6.

(c) Sodium thiosulfate

Sodium thiosulfate contains two sodium atoms (Na), one sulfur atom (S), and three oxygen atoms (O). The chemical formula for this compound is \(\text{Na}_2\text{S}_2\text{O}_3\). Now, to find the oxidation state of sulfur: Each sodium atom has an oxidation state of +1, so two sodium atoms will have a total oxidation state of +2. Each oxygen atom has an oxidation state of -2, so three oxygen atoms will have a total oxidation state of -6. As the total oxidation state for sulfur will balance that of sodium and oxygen, the oxidation state of two sulfur atoms will be +4. Thus, for a single sulfur atom, the oxidation state in sodium thiosulfate is +2.

(d) Hydrogen sulfide

Hydrogen sulfide contains two hydrogen atoms (H) and one sulfur atom (S). The chemical formula for this compound is \(\text{H}_2\text{S}\). Now, to find the oxidation state of sulfur: Each hydrogen atom has an oxidation state of +1, so two hydrogen atoms will have a total oxidation state of +2. As the sulfur atom needs to balance the oxidation state, it will have an oxidation state of -2. Hence, the oxidation state of sulfur in \(\text{H}_2\text{S}\) is -2.

(e) Sulfuric acid

Sulfuric acid contains two hydrogen atoms (H), one sulfur atom (S), and four oxygen atoms (O). The chemical formula for this compound is \(\text{H}_2\text{SO}_4\). Now, to find the oxidation state of sulfur: Each hydrogen atom has an oxidation state of +1, so two hydrogen atoms will have a total oxidation state of +2. Each oxygen atom has an oxidation state of -2, so four oxygen atoms will have a total oxidation state of -8. As the sulfur atom needs to balance the oxidation state, it will have an oxidation state of +6. Hence, the oxidation state of sulfur in \(\text{H}_2\text{SO}_4\) is +6.

(f) Sulfur dioxide

Sulfur dioxide contains one sulfur atom (S) and two oxygen atoms (O). The chemical formula for this compound is \(\text{SO}_2\). Now, to find the oxidation state of sulfur: Each oxygen atom has an oxidation state of -2, so two oxygen atoms will have a total oxidation state of -4. As the sulfur atom needs to balance the oxidation state, it will have an oxidation state of +4. Hence, the oxidation state of sulfur in \(\text{SO}_2\) is +4.

(g) Mercury telluride

Mercury telluride contains one mercury atom (Hg) and one tellurium atom (Te). The chemical formula for this compound is \(\text{HgTe}\). Now, to find the oxidation state of tellurium: Mercury has an oxidation state of +2. As the tellurium atom needs to balance the oxidation state, it will have an oxidation state of -2. Hence, the oxidation state of tellurium in \(\text{HgTe}\) is -2.

Key concepts

Oxidation States

Oxidation states, also known as oxidation numbers, are fundamental in understanding how atoms interact in chemical compounds. They offer a way to track electron transfers among atoms in a reaction. Typically, oxidation state indicates how many electrons an atom has gained or lost compared to its neutral state. For instance, if an atom loses electrons, it acquires a positive oxidation state, while gaining electrons results in a negative oxidation state.

Let’s consider some rules often used for assigning oxidation states:

• The oxidation state of an atom in a free element is always zero. For example, the oxidation state for both O in O₂ and S in S₈ is 0.
• For ions consisting of only one atom, the oxidation state is equal to the charge of the ion.
• In compounds, hydrogen is usually assigned an oxidation state of +1 and oxygen -2, with some exceptions.
• The sum of oxidation states for all atoms in a neutral compound must be zero, while for ions, it should equal the ionic charge.

Understanding these simple guidelines can help predict the stability and reactivity of compounds, especially those involving redox reactions, where electron transfer is a key feature.

Group 6A Elements

Group 6A elements, also known as the chalcogens, include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). These elements are p-block elements in the periodic table, positioning them just below nitrogen's group.

The chalcogens are known for their ability to form a variety of oxidation states, which makes them versatile in forming various compounds. The most common and stable oxidation states for sulfur, for example, are -2, +4, and +6. This versatility arises due to their electron configuration that enables sulfur and its congeners to gain or share electrons easily.

These elements are notable for their significant role in biological systems and industrial processes. For instance, sulfur is a key component in amino acids and proteins, whereas selenium is important for certain enzymes.

• Oxygen is most commonly encountered in the -2 oxidation state in compounds.
• Sulfur can frequently appear in oxidation states of -2 (as in H₂S) and +6 (as in H₂SO₄).
• Selenium and tellurium have similar chemistry and can be in oxidation states ranging from -2 to +6.

This variety allows the chalcogens to participate in a wide range of chemical reactions and applications.

Sulfur Compounds

Sulfur compounds play a crucial role in both biological systems and industry. In chemistry, sulfur is a highly versatile element capable of forming compounds with numerous oxidation states and bonding types.

Some common sulfur-containing compounds and their applications include:

• Hydrogen sulfide (H₂S): A gaseous compound with a -2 oxidation state for sulfur, notorious for its rotten egg smell, and important in biological waste processes.
• Sulfur dioxide (SO₂): In this compound, sulfur has a +4 oxidation state. Usually found as a pollutant, it is also used in bleaching and as a preservative.
• Sulfuric acid (H₂SO₄): Known for its +6 oxidation state of sulfur, it’s one of the most widely used industrial chemicals in the manufacture of fertilizers, chemicals, and in refining oil.

Understanding these compounds is vital, given their far-reaching implications across environmental, industrial, and biological contexts.