Question

Aluminum forms compounds with both sulfur and oxygen. Why are the formulas of the resulting compounds \(\mathrm{Al}_{2} \mathrm{~S}_{3}\) and \(\mathrm{Al}_{2} \mathrm{O}_{3}\), respectively? Why are the formulas similar?

Short answer

The formulas of the resulting compounds Al₂S₃ and Al₂O₃ are similar because both sulfur and oxygen have a valency of -2, and aluminum has a valency of +3. To balance the charges, we need 2 aluminum atoms (+3 charge each) and 3 atoms of either sulfur or oxygen (-2 charge each), resulting in a balanced charge of +6 from aluminum and -6 from either sulfur or oxygen. Since both sulfur and oxygen have the same valency and can form compounds with aluminum in the same way, the formulas for these compounds are similar.

Step-by-step solution

Identify the valency of the elements involved

To understand why these compounds have the formulas they do, we first need to determine the valency of aluminum, sulfur, and oxygen. The valency of an element is the number of electrons it can either gain, lose, or share in order to form a stable compound with another element. We can find the valency by looking at the periodic table: - Aluminum (Al) is in Group 13, so it has a valency of +3. - Sulfur (S) is in Group 16, so it has a valency of -2. - Oxygen (O) is also in Group 16, so it has a valency of -2 as well.

Combine the valencies to form compounds

Now that we know the valencies of the elements, we can determine the formulas of the compounds they form by combining them in such a way that the overall charges balance out. For the compound formed between aluminum and sulfur (Al and S): - Aluminum has a valency of +3 and sulfur has a valency of -2. - To balance the charges, we need 2 aluminum atoms (+3 charge each) and 3 sulfur atoms (-2 charge each). - This results in a total charge of +6 from aluminum and -6 from sulfur, balancing the charges. - Thus, the formula for this compound is Al₂S₃. For the compound formed between aluminum and oxygen (Al and O): - Aluminum has a valency of +3 and oxygen has a valency of -2. - To balance the charges, we need 2 aluminum atoms (+3 charge each) and 3 oxygen atoms (-2 charge each). - This results in a total charge of +6 from aluminum and -6 from oxygen, balancing the charges. - Thus, the formula for this compound is Al₂O₃.

Analyze the similarity in the formulas

Now that we have the formulas for both compounds, Al₂S₃ and Al₂O₃, we can analyze the reason behind their similarity: - Both compounds involve aluminum, which has a valency of +3. - Both sulfur and oxygen have valencies of -2. - In both cases, the charges are balanced by combining 2 aluminum (+3 charge each) atoms with 3 atoms of either sulfur or oxygen (-2 charge each). - This results in a balanced charge of +6 from aluminum and -6 from either sulfur or oxygen. Since both sulfur and oxygen have the same valency and can form compounds with aluminum in the same way, the formulas for these compounds, Al₂S₃ and Al₂O₃, are similar.

Key concepts

Valency and Chemical Bonding

Valency is fundamental to understanding chemical bonding and the formation of compounds. The valency of an element represents its ability to form bonds with other elements, based on the number of electrons it needs to gain, lose, or share to achieve a full outer shell - a state of stability according to the octet rule. For instance, aluminum has a valency of +3. It seeks to lose three electrons to obtain a stable configuration. On the other hand, sulfur and oxygen, both located in Group 16 of the periodic table, have a valency of -2, indicating a tendency to gain two electrons to complete their outer shell.

When elements with opposite valencies interact, they tend to form chemical bonds to stabilize themselves. This is the core principle behind the formation of compounds like aluminum sulfide (\(\mathrm{Al}_{2}\mathrm{S}_{3}\)) and aluminum oxide (\(\mathrm{Al}_{2}\mathrm{O}_{3}\)). Aluminum needs to lose electrons which sulfur or oxygen can accept. Due to the +3 charge of aluminum and the -2 charge of both sulfur and oxygen, the ratio of atoms in resulting compounds must balance out the overall charge, resulting in the observed formulas of \(\mathrm{Al}_{2}\mathrm{S}_{3}\) and \(\mathrm{Al}_{2}\mathrm{O}_{3}\).

Aluminum Compounds

Aluminum, a metal with valency +3, reacts with nonmetals to form various compounds. Two such compounds are aluminum sulfide and aluminum oxide. To write the chemical formulas for these compounds, we must consider the charge balance. Aluminum, having a +3 charge, must bond with sulfur or oxygen atoms that collectively provide a counterbalance. A pair of aluminum atoms together have a total charge of +6, requiring three sulfur or oxygen atoms, each with a charge of -2, to balance the charge and form neutral compounds. Hence, we get the stable compounds \(\mathrm{Al}_{2}\mathrm{S}_{3}\) and \(\mathrm{Al}_{2}\mathrm{O}_{3}\).

In addition to forming compounds with sulfur and oxygen, aluminum can react with other nonmetals and even some metals, creating a wide array of compounds important in industries ranging from construction to pharmaceuticals.

Periodic Table and Element Groups

The periodic table is an illustrious tool organizing elements based on their chemical properties, most notably atomic number and valency. Elements are grouped into 18 vertical columns known as groups. Elements in the same group typically have the same valency and similar chemical behaviors. For example, aluminum is situated in Group 13, which contains elements with a valency of +3, while sulfur and oxygen belong to Group 16, consisting of elements mostly with a valency of -2.

The horizontal rows are called periods and elements within a period share the same number of electron shells. Taking aluminum compounds as an example, understanding its position in Group 13 helps us predict its bonding behavior, including its trivalent nature, which directly influences the compounds it forms. Recognizing pattern in valency across the periodic table is critical for students to predict and comprehend the structure of more complex compounds.