Question

Using the periodic table to guide you, predict the chemical formula and name of the compound formed by the following elements: (a) Ga and \(\mathrm{F}\), (b) \(\mathrm{Li}\) and \(\mathrm{H}\), (c) Al and \(\mathrm{I}\), (d) \(\mathrm{K}\) and \(\mathrm{S}\).

Short answer

The chemical formulas and names of the compounds formed by the given elements are: (a) GaF3 - Gallium trifluoride (b) LiH - Lithium hydride (c) AlI3 - Aluminum triiodide (d) K2S - Potassium sulfide

Step-by-step solution

(Step 1: Identify charges of elements using periodic table)

To determine the charges of the ions formed by each element, we need to determine their group in the periodic table. Elements in the same group have the same number of valence electrons and tend to form ions with the same charge. (a) Ga and F Ga (Gallium): Group 13, forms +3 ions F (Fluorine): Group 17, forms -1 ions (b) Li and H Li (Lithium): Group 1, forms +1 ions H (Hydrogen): Group 1, forms -1 ions when bonded with metallic elements (c) Al and I Al (Aluminum): Group 13, forms +3 ions I (Iodine): Group 17, forms -1 ions (d) K and S K (Potassium): Group 1, forms +1 ions S (Sulfur): Group 16, forms -2 ions

(Step 2: Determine the chemical formula for each compound)

We use the charges of the ions to find the ratio of the elements in the compound such that the overall charge of the compound is neutral. (a) Ga (+3) and F (-1) To balance the charge, we need 3 F ions for each Ga ion, so the chemical formula is GaF3. (b) Li (+1) and H (-1) To balance the charge, we need 1 H ion for each Li ion, so the chemical formula is LiH. (c) Al (+3) and I (-1) To balance the charge, we need 3 I ions for each Al ion, so the chemical formula is AlI3. (d) K (+1) and S (-2) To balance the charge, we need 2 K ions for each S ion, so the chemical formula is K2S.

(Step 3: Determine the name of each compound)

We can now write the names of the compounds using their respective chemical formulas. (a) GaF3 - Gallium trifluoride (b) LiH - Lithium hydride (c) AlI3 - Aluminum triiodide (d) K2S - Potassium sulfide

Key concepts

Periodic Table Charge Analysis

Understanding how to analyze the periodic table for ion charge is essential for predicting chemical formulas. Elements are organized into groups that share similar chemical properties, including the tendency to form ions with specific charges.

Groups 1, 2, and 13 to 18 are the main groups relevant to charge determination. Group 1 elements like Li (Lithium) tend to lose one electron to form +1 ions. Moving to Group 2, elements such as magnesium would typically lose two electrons to form +2 ions. When you reach Group 13, like Ga (Gallium), elements form +3 ions.

Conversely, the groups furthest to the right in the periodic table gain electrons to achieve a full outer shell. Group 17, including elements like F (Fluorine), usually gains one electron to form -1 ions. Group 16, with elements like S (Sulfur), tends to gain two electrons, resulting in -2 ions.

The transitional metals, not covered here, can form multiple ion charges and require additional context for accurate charge determination.

Ion Charge Determination

Ion charge determination is a pivotal step in predicting the chemical formulas of compounds. An ion is formed when an atom gains or loses electrons, resulting in a negatively or positively charged entity. The goal is to achieve a noble gas electron configuration, which is often the most stable.

For example, in the gallium fluoride (GaF3) compound, Gallium (Ga) forms a +3 ion by losing three electrons. Fluorine (F), needing one electron to fill its valence shell, forms a -1 ion. By recognizing the charge of each ion, we can determine the ratios in which these ions combine to form a neutral compound.

When dealing with metals that can form multiple ion charges, such as transition metals, often the compound's context or Roman numerals in the compound's name can aid in determining the correct ion charge.

Binary Compound Nomenclature

Binary compound nomenclature refers to the naming system for compounds consisting of two different elements. The name of the compound traditionally starts with the positive ion (cation) followed by the negative ion (anion).

The cation retains the name of the element, like lithium in Lithium hydride (LiH). The anion's name is derived from the root of the element's name with an 'ide' suffix, as seen with fluoride in Gallium trifluoride (GaF3).

For more complex ions, like those of transition metals that can form more than one possible charge, the charge is specified using Roman numerals. However, for the main group elements in binary compounds, only the 'ide' suffix is necessary to indicate the type of anion present.

When dealing with multiple anions, prefixes such as 'tri-' in Aluminum triiodide (AlI3) may be used to indicate the number of anions in the compound.