Question

Determine the number of protons and electrons in each ion. (a) \(\mathrm{Al}^{3+}\) (b) \(S^{2-}\) (c) \(\mathrm{I}^{-}\) (d) \(\mathrm{Ag}^{+}\)

Short answer

\(\mathrm{Al}^{3+}\): 13 protons, 10 electrons. \(S^{2-}\): 16 protons, 18 electrons. \(\mathrm{I}^{-}\): 53 protons, 54 electrons. \(\mathrm{Ag}^{+}\): 47 protons, 46 electrons.

Step-by-step solution

Understanding Ions and their Charges

An ion is an atom or a molecule with a net electric charge due to the loss or gain of one or more electrons. A cation is a positively charged ion (more protons than electrons), and an anion is a negatively charged ion (more electrons than protons). The charge of the ion indicates the difference between the number of protons and electrons.

Determining Protons and Electrons for \(\mathrm{Al}^{3+}\)

Aluminum (Al) has an atomic number of 13, which means it has 13 protons. As an \(\mathrm{Al}^{3+}\) ion, it has lost 3 electrons, so it has 10 electrons.

Determining Protons and Electrons for \(S^{2-}\)

Sulfur (S) has an atomic number of 16, meaning it has 16 protons. As an \(S^{2-}\) ion, it has gained 2 electrons, so it has 18 electrons.

Determining Protons and Electrons for \(\mathrm{I}^{-}\)

Iodine (I) has an atomic number of 53, indicating it has 53 protons. As an \(\mathrm{I}^{-}\) ion, it has gained 1 electron, so it has 54 electrons.

Determining Protons and Electrons for \(\mathrm{Ag}^{+}\)

Silver (Ag) has an atomic number of 47, which means it has 47 protons. As an \(\mathrm{Ag}^{+}\) ion, it has lost 1 electron, so it has 46 electrons.

Key concepts

Determining Protons and Electrons

When we are talking about atoms, each atom is defined by its atomic number, which tells us the number of protons in its nucleus. Protons are positively charged particles, and this positive charge is balanced by the same number of electrons, which are negatively charged, when the atom is neutral.

However, atoms can lose or gain electrons through various processes, turning them into ions. When an atom loses electrons, it becomes a positively charged ion, known as a cation. Conversely, when an atom gains electrons, it becomes negatively charged, called an anion.

To determine the number of protons and electrons in an ion, we start with its atomic number, which provides the number of protons. Then, we adjust the number of electrons based on the ion's charge. For example, a positively charged ion with a charge of +2 (cation) will have two less electrons than protons. On the other hand, a negatively charged ion with a charge of -2 (anion) will have two more electrons than protons.

It's essential to grasp this balance to understand how ions interact in chemical reactions and create compounds. By practicing with various elements, young scientists can become proficient in predicting the behavior of ions.

Cation and Anion

Understanding the difference between cations and anions is crucial for anyone studying chemistry.

Cations

These are positively charged ions that are created when an atom loses one or more electrons. This means that cations have more protons than electrons. They are typically formed by metals which easily give up electrons. A common example is sodium in table salt, where sodium exists as a cation (Na+).

Anions

These are negatively charged ions, formed when an atom gains one or more electrons, indicating that they have more electrons than protons. Non-metals often form anions, such as chlorine becoming the chloride ion (Cl-) in table salt.

Knowing the charge on ions is crucial because it helps in understanding the type of bonding occurring in compounds, the compound's electrical conductance, and predicting the reactions the ion may engage in.

Atomic Number

The atomic number of an element is perhaps the most fundamental property in understanding chemical behavior. It is designated as 'Z' and uniquely identifies an element. The atomic number is equal to the number of protons found in the nucleus of an atom of that element. Since electrons and protons have equal but opposite charges, a neutral atom will have an equal number of protons and electrons.

For ions, the atomic number remains constant since it is based on protons, which do not change in number. However, the number of electrons will differ from the atomic number in ions due to the gain or loss of electrons. This change is what leads to the formation of cations and anions.

Remember, the atomic number is also the key to the element's position on the periodic table, defining its chemical behavior and its place in the periodic law. For instance, elements with similar chemical properties fall into the same group or column, showcasing the periodic tables' power as a tool for predicting the characteristics of elements.