Write formulas for the ionic compounds formed from \(\mathrm{Cl}^{-}\) and (a) cadmium ion, (b) silver ion, (c) zinc ion, and (d) nickel ion.

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions. These ions are atoms that have gained or lost electrons, thus acquiring a charge. Metals tend to lose electrons and form positively charged ions, known as cations, while non-metals tend to gain electrons and form negatively charged ions, or anions.

When an ionic bond is formed, the cations and anions are held together by the strong force of attraction between their opposite charges. For example, in a sodium chloride (NaCl) structure, each sodium ion (Na+) is surrounded by and attracted to chloride ions (Cl−), and this pattern repeats, forming a crystal lattice that extends in all three dimensions.

This lattice structure is what gives ionic compounds their characteristic high melting and boiling points, as a lot of energy is required to break these strong ionic bonds. Ionic compounds typically dissolve in polar solvents like water, releasing the ions, which is important for conducting electricity when in solution or in molten form.

Chemical formulas represent the types and numbers of atoms in a substance. An ionic compound's formula is a concise way of expressing which ions are in the compound and in what proportions. The goal is to combine cations and anions in a way that the overall charge is zero, resulting in a neutral compound.

For instance, the ionic compound formed between cadmium ions (Cd^{2+}) and chloride ions (Cl−) is represented by the formula CdCl_2. This indicates that there are two chloride ions for each cadmium ion, balancing the charges to make an electrically neutral compound.

Understanding how to write chemical formulas requires knowledge of the charges of the ions involved. When combining ions, the positive and negative charges must balance out, which sometimes requires using multiple copies of one ion, as seen in the formula ZnCl_2, where two chloride ions are needed to balance the two positive charges of a single zinc ion (Zn^{2+}).

The valency of an element is a measure of its ability to combine with other atoms, indicating the number of electrons an atom can lose, gain, or share to form a stable compound. In ionic bonding, valency specifically refers to the combining power of an ion, corresponding to the charge on the ion.

For example, the cadmium ion (Cd^{2+}) has a valency of 2, reflecting its ability to combine with two chloride ions (Cl−) to form CdCl_2. In the case of a silver ion (Ag+), it has a valency of 1, therefore it combines with only one chloride ion to form AgCl.

A cation like the zinc ion (Zn^{2+}) also has a valency of 2, so to achieve charge neutrality, the resulting formula is ZnCl_2. Similarly, nickel in the +2 oxidation state (Ni^{2+}) can bond with two chloride ions, resulting in the compound NiCl_2. Recognizing the valency of elements is crucial in predicting how different atoms will bond and in writing accurate chemical formulas.