Question

For the following processes that show the formation of ions, use the periodic table to indicate the number of electrons and protons present in both the \(i o n\) and the neutral atom from which the ion is made. a. \(\mathrm{Ca} \rightarrow \mathrm{Ca}^{2+}+2 \mathrm{e}^{-}\) b. \(\mathrm{P}+3 \mathrm{e}^{-} \rightarrow \mathrm{P}^{3-}\) c. \(\mathrm{Br}+\mathrm{e}^{-} \rightarrow \mathrm{Br}^{-}\) d. \(\mathrm{Fe} \rightarrow \mathrm{Fe}^{3+}+3 \mathrm{e}^{-}\) e. \(\mathrm{Al} \rightarrow \mathrm{Al}^{3+}+3 \mathrm{e}^{-}\) f. \(\mathrm{N}+3 \mathrm{e}^{-} \rightarrow \mathrm{N}^{3-}\)

Short answer

a. Neutral Ca: 20 protons, 20 electrons; \(Ca^{2+}\) ion: 20 protons, 18 electrons b. Neutral P: 15 protons, 15 electrons; \(P^{3-}\) ion: 15 protons, 18 electrons c. Neutral Br: 35 protons, 35 electrons; \(Br^{-}\) ion: 35 protons, 36 electrons d. Neutral Fe: 26 protons, 26 electrons; \(Fe^{3+}\) ion: 26 protons, 23 electrons e. Neutral Al: 13 protons, 13 electrons; \(Al^{3+}\) ion: 13 protons, 10 electrons f. Neutral N: 7 protons, 7 electrons; \(N^{3-}\) ion: 7 protons, 10 electrons

Step-by-step solution

Identify the element and ion

Refer to the periodic table and find the element Calcium (Ca). Calcium is in group 2, and its atomic number is 20.

Calculate the number of protons and electrons for the neutral atom

Since the atomic number of Calcium is 20, the number of protons in a neutral Calcium atom is 20. In a neutral atom, the number of electrons equals the number of protons, so there are 20 electrons in the neutral Calcium atom.

Calculate the number of electrons for the ion

When Calcium forms a \(2+\) ion, it loses 2 electrons. Therefore, the number of electrons in the \(Ca^{2+}\) ion is 20 - 2 = 18.

Final answer

In the neutral Calcium atom, there are 20 protons and 20 electrons. In the \(Ca^{2+}\) ion, there are 20 protons and 18 electrons. Repeat the process for the other lettered problems b. \(\mathrm{P}+3 \mathrm{e}^{-} \rightarrow \mathrm{P}^{3-}\) c. \(\mathrm{Br}+\mathrm{e}^{-} \rightarrow \mathrm{Br}^{-}\) d. \(\mathrm{Fe} \rightarrow \mathrm{Fe}^{3+}+3 \mathrm{e}^{-}\) e. \(\mathrm{Al} \rightarrow \mathrm{Al}^{3+}+3 \mathrm{e}^{-}\) f. \(\mathrm{N}+3 \mathrm{e}^{-} \rightarrow \mathrm{N}^{3-}\)

Key concepts

Periodic Table

The periodic table is a comprehensive chart that organizes all known elements according to their atomic number, which is the number of protons present in the nucleus of an atom. Elements are arranged in rows called periods and columns known as groups.

Each element has a unique place on the table and is represented by a one- or two-letter symbol. The periodic table provides valuable information at a glance, such as an element's atomic mass and its typical chemical behavior. When studying the formation of ions, the periodic table becomes an indispensable tool. It helps us understand how elements are likely to react and what ions they can form based on their position in the table. For example, elements in group 1 are likely to form +1 ions while those in group 17 tend to form -1 ions.

Using the Periodic Table for Ion Formation

The periodic table not only shows us the atomic number of an element but also its tendency to lose or gain electrons to reach a stable electron configuration. This process is indicative of the formation of positive or negative ions, respectively. The groups and periods give us hints about the number of valence electrons which are the electrons available to be lost, gained, or shared in the formation of chemical bonds.

Atomic Number

The atomic number is one of the key pieces of information the periodic table provides about an element. Simply put, the atomic number is the number of protons in the nucleus of an atom and it defines the identity of the element. For instance, all atoms with 20 protons are calcium atoms. This number is important because it does not change—even when the atom forms ions.

When an atom transforms into an ion, it loses or gains electrons but the number of protons remains the same. This distinction is crucial when identifying ions and understanding their formation. In ions, while the number of electrons may change, leading to a positive or negative charge, the atomic number remains constant ensuring that the elemental identity is preserved. Protons, being positively charged, balance out the negative charge of the electrons in a neutral atom. However, when an imbalance occurs due to electron transfer, we get ions with net charges.

Importance in Ion Formation

Understanding atomic number helps to ensure accuracy when determining the charge of ions. As the atomic number remains unchanged, it serves as a reference point for calculating the number of electrons in ions after ionization occurs.

Electron Configuration

Electron configuration refers to the arrangement of electrons in an atom's electron shells. Shells are designated by numbers (1, 2, 3, etc.), and within these shells, there are subshells identified by letters (s, p, d, f). The electrons fill these subshells according to specific rules, such as the Aufbau principle, which tells us that electrons occupy the lowest energy level available.

Electron configuration is pivotal in predicting the chemical behavior of an element. An element tends to be more chemically stable when its outer shell is full. For example, noble gases have full outer shells and are notably inert. When atoms form ions, they do so by gaining or losing electrons to achieve a more stable electron configuration similar to that of a noble gas. This is known as the octet rule for elements in the main groups of the periodic table.

Role in Formation of Ions

In the context of ions, knowing an element's electron configuration allows us to predict which ions an element will form to achieve stability. For instance, calcium commonly loses two electrons to achieve the electron configuration of argon, resulting in a positively charged calcium ion (Ca2+). By contrast, an element like sulfur will gain two electrons to attain the electron configuration of argon, resulting in a negatively charged sulfate ion (S2-). Electron configuration is, therefore, fundamental in explaining the transfer of electrons during the formation of ions.