Question

Predict the chemical formula for each of the following binary ionic compounds given the formula of aluminum nitride, AlN: (a) gallium nitride (b) aluminum arsenide

Short answer

The chemical formula for gallium nitride is GaN, and for aluminum arsenide, it is AlAs.

Step-by-step solution

Understand the Compound Components

Each compound is made up of a metal cation and a non-metal anion. Here, we start with gallium nitride. Gallium (Ga) is in the same group as aluminum, so they share similar properties, specifically the charge when forming compounds.

Determine Ion Charges for Gallium Nitride

Gallium, like aluminum, forms a +3 charge in ionic compounds because it's in Group 13 of the periodic table. Nitrogen forms a -3 charge because it gains three electrons to achieve a stable electronic configuration (like noble gases).

Write the Chemical Formula for Gallium Nitride

To write the formula, combine the cation Ga with the anion N such that overall the charges balance to zero: Ga^{3+} and N^{3-} combine to form GaN.

Understand the Compound Components for Aluminum Arsenide

Like the previous step, for aluminum arsenide, we're combining aluminum and arsenide. Aluminum forms a +3 ion while arsenic (in the form of arsenide), being a non-metal element also in group 15 like nitrogen, forms a -3 ion.

Determine the Formula for Aluminum Arsenide

Similarly to aluminum nitride's formula, the charges of the ions must neutralize each other: Al^{3+} and As^{3-}. Therefore, the formula is AlAs.

Key concepts

Binary Ionic Compounds

Binary ionic compounds are a type of chemical compound that consists of two different elements: one metal and one non-metal. The term 'binary' signifies that there are only two different types of elements involved in the compound.
These compounds are generally formed when a metallic element combines with a non-metallic element. The metal acts as a cation, which means it loses electrons and carries a positive charge. On the other hand, the non-metal acts as an anion, gaining electrons and carrying a negative charge. Opposite charges attract, leading to the formation of a stable compound.
For instance, in the case of gallium nitride (GaN) and aluminum nitride (AlN), gallium and aluminum are metals that form positive cations, whereas nitrogen is a non-metal that forms a negative anion. The process through which these ions form involves electronic exchanges aimed at achieving electronic configurations similar to noble gases, which are very stable.

Ion Charges

Ion charges are integral in understanding how elements combine to form binary ionic compounds. Metals usually lose electrons to become positively charged cations. Non-metals, on the other hand, typically gain electrons to become negatively charged anions.
For example:

• Gallium (Ga) is a metal with three electrons in its outer shell. It tends to lose these electrons to achieve a stable electronic configuration, resulting in a +3 charge (Ga^{3+}).
• Nitrogen (N) is a non-metal that prefers to gain three electrons, achieving a -3 charge (N^{3-}). This makes its electronic configuration stable like neon, a noble gas.
• Similarly, aluminum (Al) forms a +3 charge (Al^{3+}) while arsenic (As), like nitrogen, forms a -3 charge (As^{3-}).

Understanding these charges is essential for predicting how different elements will combine to form stable compounds. The objective is always to balance these charges to result in a neutral compound.

Chemical Formulas

Chemical formulas represent the composition of a compound by indicating which elements are present and the quantity of each ion. In binary ionic compounds, the chemical formula is derived by ensuring the total positive charge from the metal ions equals the total negative charge from the non-metal ions.

To write the chemical formula for compounds such as gallium nitride and aluminum arsenide, one must ensure the charges balance:

• In GaN, Ga^{3+} pairs with N^{3-}, leading to a balanced formula since +3 and -3 equal zero.
• Similarly, in AlAs, Al^{3+} neutralizes As^{3-}, resulting in a balanced and neutral compound.

Each pair of ions combines in a one-to-one ratio, maintaining neutrality. Understanding chemical formulas not only helps in writing the compound correctly but also gives insight into the compound's properties.