Question

Write the formula for each of the following simple binary ionic compounds. a. calcium chloride b. silver(I) oxide (usually called silver oxide) c. aluminum sulfide d. beryllium bromide e. hydrosulfuric acid f. potassium hydride g. magnesium iodide h. cesium fluoride

Short answer

a. CaCl\(_2\) b. Ag\(_2\)O c. Al\(_2\)S\(_3\) d. BeBr\(_2\) e. H\(_2\)S f. KH g. MgI\(_2\) h. CsF

Step-by-step solution

a. Calcium chloride

Calcium is a metal in Group 2 of the periodic table and has a valency of +2. Chlorine is a non-metal in Group 17 and has a valency of -1. To balance the charges and form a neutral compound, the formula for calcium chloride is CaCl\(_2\).

b. Silver(I) oxide (usually called silver oxide)

Silver(I) indicates silver with a valency of +1. Oxide refers to oxygen, which has a valency of -2. Balancing the charges to form a neutral compound, the formula for silver(I) oxide is Ag\(_2\)O.

c. Aluminum sulfide

Aluminum is a metal in Group 13 and has a valency of +3. Sulfide refers to sulfur, which has a valency of -2. Balancing the charges for a neutral compound, the formula for aluminum sulfide is Al\(_2\)S\(_3\).

d. Beryllium bromide

Beryllium is a metal in Group 2 and has a valency of +2. Bromide refers to bromine, which has a valency of -1. Balancing the charges for a neutral compound, the formula for beryllium bromide is BeBr\(_2\).

e. Hydrosulfuric acid

Hydrosulfuric acid can be better understood as hydrogen sulfide. Hydrogen has a valency of +1, and sulfur has a valency of -2. To balance the charges for a neutral compound, the formula for hydrosulfuric acid, or hydrogen sulfide, is H\(_2\)S.

f. Potassium hydride

Potassium is a metal in Group 1 of the periodic table and has a valency of +1. Hydride refers to hydrogen, which has a valency of -1 when it is a part of a compound with a metal. The charges are already balanced, so the formula for potassium hydride is KH.

g. Magnesium iodide

Magnesium is a metal in Group 2 and has a valency of +2. Iodide refers to iodine, which has a valency of -1. Balancing the charges for a neutral compound, the formula for magnesium iodide is MgI\(_2\).

h. Cesium fluoride

Cesium is a metal in Group 1 of the periodic table and has a valency of +1. Fluoride refers to fluorine, which has a valency of -1. The charges are already balanced, so the formula for cesium fluoride is CsF.

Key concepts

Chemical Formula

A chemical formula is a simple way of indicating the elements present in a compound, as well as their proportions. It is composed of the chemical symbols of the elements and numerical subscripts representing the number of atoms of each element in the molecule. For example, in the molecule of water, \(\text{H}_2\text{O}\), two hydrogen atoms and one oxygen atom make up the compound.

• Elements are represented by their symbols from the periodic table.
• Subscripts are used to show how many atoms of each element are present.
• No subscript means one atom of that element.

Understanding chemical formulas helps us grasp how molecules are structured and what changes occur during chemical reactions.

Valency

Valency is the measure of an element's ability to bond with other elements. It's based on the number of electrons an atom can gain, lose, or share to achieve a full outer shell. Valency determines how elements combine to form compounds. Metals and non-metals usually have positive and negative valencies, respectively. For example:

• Calcium, a Group 2 metal, has a valency of \(+2\).
• Chlorine, a non-metal from Group 17, carries a valency of \(-1\).

Valency is crucial in determining the formula of a compound, ensuring that the molecules formed are balanced and stable. The sum of the valencies in a compound must equal zero, resulting in a neutral compound.

Neutral Compound

A neutral compound means that the total positive charge from the cations (positively charged ions) equals the total negative charge from the anions (negatively charged ions). This balance is essential for the stability of the compound. For example, in calcium chloride, \(\text{CaCl}_2\), calcium has a charge of \(+2\) and each chlorine has a charge of \(-1\). Thus, the formula requires two chlorine atoms to balance one calcium atom, resulting in a net charge of zero:

• 1 calcium (\(+2\)) + 2 chlorines (\(-1\), each) = 0
• Neutral compounds are stable and do not have any overall electrical charge.

Achieving a neutral charge is fundamental when writing chemical formulas for ionic compounds.

Periodic Table

The periodic table is an organized chart of elements, showcasing essential information, such as atomic numbers, symbols, and valency trends. This classification aids in predicting chemical behavior and reactions. Elements are arranged in increasing atomic number and grouped by similar properties. Here's how it assists in determining chemical formulas and properties:

• Groups (columns) share chemical properties and valencies; for example, Group 1 elements (alkali metals) have a valency of \(+1\).
• Periods (rows) indicate elements with the same number of electron shells.

The periodic table is a powerful tool, simplifying the prediction of the elements' chemical behaviors, which is crucial in understanding how they form compounds.

Chemical Nomenclature

Chemical nomenclature refers to the system of naming chemical compounds. It's important for ensuring clarity and understanding across the scientific community. For binary ionic compounds, names are generally structured as: ``name of metal + (charge if necessary) + name of non-metal + 'ide'``.
For example, in the compound calcium chloride:

• "Calcium" is the name of the metal.
• "Chloride" is derived from chlorine, with the ending "-ide" indicating it is a non-metal anion.

Chemical nomenclature provides a standardized method of referring to compounds, ensuring effective communication in the scientific world. This is particularly helpful when discussing the properties and reactions of substances.