Predict the chemical formula of the ionic compound formed between the following pairs of elements: (a) Al and F

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Identify the charges of the ions formed by each element: Aluminum (Al) typically forms a cation with a charge of +3, denoted as \( \text{Al}^{3+} \). Fluorine (F) typically forms an anion with a charge of -1, denoted as \( \text{F}^{-} \).

Determine the ratio of cations to anions needed to balance the overall charge of the compound. Since aluminum has a +3 charge and fluorine has a -1 charge, you will need three fluoride ions to balance the charge of one aluminum ion.

Write the chemical formula by combining the ions in the ratio determined in the previous step. The subscript for each ion in the formula indicates the number of each ion needed to balance the charges.

The chemical formula is written by placing the cation first followed by the anion, with the appropriate subscripts to indicate the number of each ion. In this case, the formula is \( \text{AlF}_3 \).

Double-check the charges to ensure the compound is neutral. The total positive charge from one \( \text{Al}^{3+} \) is +3, and the total negative charge from three \( \text{F}^{-} \) is -3, resulting in a neutral compound.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ionic Bonding

Ionic bonding occurs when atoms transfer electrons to achieve full outer electron shells, resulting in the formation of charged ions. Typically, metals lose electrons to become positively charged cations, while nonmetals gain electrons to become negatively charged anions. The electrostatic attraction between these oppositely charged ions forms the ionic compound.

Valency

Valency refers to the ability of an atom to bond with other atoms, determined by the number of electrons in its outer shell. For aluminum (Al), which has a valency of +3, it can lose three electrons, while fluorine (F), with a valency of -1, can gain one electron. Understanding valency is crucial for predicting the ratios of ions in an ionic compound.

Chemical Formula

A chemical formula represents the types and numbers of atoms in a compound. In ionic compounds, the formula is derived from the charges of the ions involved. For aluminum and fluorine, the formula is determined by balancing the total positive and negative charges, leading to the formula AlF3, indicating one aluminum ion and three fluoride ions.