Problem 15 - Chemistry: The Central Science

Question

Predict the chemical formula of the ionic compound formed between the following pairs of elements: (a) \(\mathrm{Al}\) and \(\mathrm{F}\), (b) \(\mathrm{K}\) and \(\mathrm{S}\), (c) \(\mathrm{Y}\) and \(\mathrm{O}\), (d) \(\mathrm{Mg}\) and \(\mathrm{N}\).

Step-by-Step Solution

Answer

The chemical formulas of the ionic compounds formed between the given pairs of elements are: (a) \(AlF_3\), (b) \(K_2S\), (c) \(Y_2O_3\), and (d) \(Mg_3N_2\).

Step 1: Identify the valency of elements

First, we need to determine the valency of each element by looking at its group in the periodic table: a) Al and F: Al - Group 13, Valency +3; F - Group 17, Valency -1 b) K and S: K - Group 1, Valency +1; S - Group 16, Valency -2 c) Y and O: Y - Group 3, Valency +3; O - Group 16, Valency -2 d) Mg and N: Mg - Group 2, Valency +2; N - Group 15, Valency -3

Step 2: Apply the electrostatic balance principle

Next, we write the chemical formula for each ionic compound such that the sum of the positive and negative charges is equal to zero (total charge on the compound should be zero). a) Al(+3) and F(-1): \(AlF_3\) b) K(+1) and S(-2): \(K_2S\) c) Y(+3) and O(-2): \(Y_2O_3\) d) Mg(+2) and N(-3): \(Mg_3N_2\)

Step 3: Combine to form chemical formula

Now, we can combine the symbols of the elements and the subscripts (which indicate the number of atoms of each element in a compound) to write the chemical formula of the ionic compound: a) Aluminum Fluoride: \(AlF_3\) b) Potassium Sulfide: \(K_2S\) c) Yttrium Oxide: \(Y_2O_3\) d) Magnesium Nitride: \(Mg_3N_2\) The chemical formulas of the ionic compounds formed between the given pairs of elements are: (a) \(AlF_3\), (b) \(K_2S\), (c) \(Y_2O_3\), and (d) \(Mg_3N_2\).

Key Concepts

Valency

Valency is a key concept in understanding how ions form ionic compounds. In simple terms, valency refers to the capability of an atom to bond with others by donating, accepting, or sharing electrons.

• It is determined by the number of valence electrons, which are the electrons available for bonding in the outermost shell of an atom.
• Group numbers in the periodic table often give a clue about the valency of an element.

For example, aluminum (Al) is in Group 13 and typically has a valency of +3, because it tends to lose three electrons to achieve stability. On the other hand, fluorine (F) is in Group 17 and typically has a valency of -1, as it tends to gain one electron to fill its outer shell. Understanding the valency is critical in predicting how different elements will react and form ionic bonds. The interaction is usually between metals, which lose electrons easily, and non-metals, which gain electrons easily.

Electrostatic Balance

Electrostatic balance is the principle that governs the formation of ionic compounds. It ensures that the total positive charges are balanced by an equal amount of negative charges, leading to a stable ionic compound.

• This is because positive ions (cations) and negative ions (anions) must balance their charges for the compound to remain electrically neutral.
• For example, if one Al ion with a +3 charge combines with three F ions, each with a -1 charge, the charges balance out: +3 from Al and 3 times -1 from F equals zero.

This balance allows the ionic compound to sustain its existence without any net electric charge, which is essential for maintaining stability in solid crystal structures and influences the physical properties of the compound when formed.

Chemical Formulas

Chemical formulas are shorthand notations used to express the elements present in a compound and the ratio in which atoms combine. For ionic compounds, these formulas represent the simplest ratio of ions that results in a neutral compound.

• A chemical formula is built using symbols of each element and subscripts to indicate the number of atoms or ions involved.
• For example, in the compound magnesium nitride, denoted as \(Mg_3N_2\), the subscripts show that three magnesium ions, each with a +2 charge, pair with two nitride ions, each with a -3 charge, resulting in a neutral compound.

Understanding chemical formulas helps in deciphering the composition and proportions of elements within a compound, which is crucial for further chemical analysis and reaction predictions. It reflects how atoms achieve electrostatic balance through ionic bonding, ensuring stability.