Question

Predict the formula for the compound aluminum nitride made from the elements aluminum and nitrogen, and explain how you made your prediction.

Short answer

The formula for the compound aluminum nitride is \(AlN\). This is predicted by determining the valencies of aluminum (+3) and nitrogen (-3) and then balancing the charges. With a 1:1 atom ratio, one aluminum atom combines with one nitrogen atom to form a neutral compound.

Step-by-step solution

Determine the valencies of aluminum and nitrogen

First, identify the valency of both elements involved in compound formation. Aluminum (Al) is in group 13 and exhibits a valency of +3, as it loses 3 electrons to achieve a stable configuration. Nitrogen (N) is in group 15 and has a valency of -3, as it gains 3 electrons to achieve a stable configuration.

Balance the charges

To find the correct formula for the compound, we need to balance the charges of both elements. Since aluminum has a charge of +3 and nitrogen has a charge of -3, the charges will balance when equal numbers of aluminum and nitrogen atoms combine. Thus, the ratio of aluminum to nitrogen atoms should be 1:1.

Write the formula for aluminum nitride

Based on the balanced charges and a 1:1 atom ratio, the formula for aluminum nitride is AlN. This means one aluminum atom combines with one nitrogen atom to form a neutrally charged compound.

Key concepts

Valency of Elements

Valency of elements plays a crucial role in understanding how different atoms combine to form compounds. This property reflects the ability of an atom to bond with other atoms, which depends on the number of electrons an atom can lose, gain, or share. In the context of the aluminum nitride example, we refer to valency as the combining power of the elements based on their electrons involved in bonding.

An element like aluminum (Al), for instance, is in group 13 of the periodic table. Elements in this group typically have three valence electrons, which they tend to lose in order to achieve a more stable electron configuration, reminiscent of the nearest noble gas. As aluminum loses three electrons, it adopts a valency of +3. Nitrogen (N), on the other hand, is found in group 15. This group is characterized by having five valence electrons and needs to gain three additional electrons to stabilize, resulting in a valency of -3 for nitrogen.

Understanding the valency of each element is essential for predicting how they will combine to form chemical compounds. Students should remember that elements seek to either lose, gain, or share electrons to maintain stability, and it is this chemical characteristic that determines the valency of an element.

Balancing Chemical Charges

Achieving a balance of chemical charges is one of the fundamental steps in predicting the formula of a compound. When elements combine to form a compound, the total positive charge must equal the total negative charge, ensuring that the overall charge of the compound is neutral.

In the case of aluminum nitride, we are dealing with aluminum ions with a +3 charge and nitrogen ions with a -3 charge. To balance these charges, we need to find the simplest ratio of aluminum to nitrogen that will result in no net charge. This turns out to be a 1:1 ratio - for every +3 charged aluminum ion, a -3 charged nitrogen ion will counterbalance that charge.

One way to help visualize this balancing act is to consider it as a seesaw where one side represents positive charges and the other negative charges. To keep the seesaw balanced (the compound neutral), the number of positive and negative charges must be equal. If every aluminum brings along three positive charges (+3) and each nitrogen brings along three negative charges (-3), then one of each will maintain the balance.

Compound Formation

Compound formation is a chemical process where two or more elements combine in a fixed ratio to form a new substance with different properties than the individual elements. The key to predicting the formula of such a compound lies in understanding the valencies and balancing the charges of the constituent elements.

Continuing with our aluminum nitride example, once we've determined the valencies of aluminum and nitrogen and balanced their charges, we can deduce the formula of the compound they form. With a 1:1 ratio established by the balance of charges, we can intuitively put the symbols of aluminum (Al) and nitrogen (N) side by side to represent that they form a compound in this exact ratio: AlN. This formula implies that in aluminum nitride, each aluminum atom is paired with a single nitrogen atom.

Compounds can have a wide array of properties, and predicting their formulas correctly is key to understanding these properties, as well as the behavior of the compounds under various conditions. It is the harmony of valency and charge balancing that facilitates the formation of stable compounds, each with its distinct chemical identity.