Give the number of protons and electrons in each of the following common ions: \(\mathrm{Na}^{+}, \mathrm{Ca}^{2+}, \mathrm{Al}^{3+}, \mathrm{Fe}^{2+}\), \(\mathrm{I}^{-}, \mathrm{F}^{-}, \mathrm{S}^{2-}, \mathrm{O}^{2-}, \mathrm{N}^{3-}\)

The atomic number of an element is a fundamental property that defines the type of atom. It tells us the number of protons present in the nucleus of an atom, which is also equal to the number of electrons in a neutral atom. Since the number of protons uniquely identifies an element, the atomic number is used to distinguish one element from another on the periodic table.

For example, sodium (Na) has an atomic number of 11, which means a neutral sodium atom has 11 protons and, consequently, 11 electrons. When forming ions, atoms can lose or gain electrons, but the number of protons—and by extension, the atomic number—remains unchanged. This concept is essential in determining the electron count for ions.

An understanding of atomic numbers is fundamental when analyzing ions. In any ion, positive or negative, the atomic number is used as the reference to determine the proton count. In educational exercises, it provides the starting point for identifying how many electrons are lost or gained to form an ion.

In chemistry, ions are atoms or molecules that have lost or gained electrons and thus have a net electric charge. Cations are positively charged ions, which means they have more protons than electrons. Conversely, anions are negatively charged ions with more electrons than protons.

When writing ion symbols, the charge is indicated by a superscript notation. For example, a sodium ion with a single positive charge is written as \(\mathrm{Na}^{+}\). This indicates that the sodium ion has lost one electron and therefore has one more proton than electrons. Similarly, a fluoride ion with a single negative charge is written as \(\mathrm{F}^{-}\), which means it has gained one electron.

Students can use the charge to determine the change in the number of electrons when compared to the neutral atom. A \(\mathrm{Ca}^{2+}\) ion has lost two electrons, while an \(\mathrm{O}^{2-}\) ion has gained two. Knowing the charge helps to calculate the electron configuration of the ion. For clarity in learning exercises, it's essential to emphasize the relationship between the charge and the gain or loss of electrons.

Electron configuration describes the distribution of electrons in the orbitals of an atom or ion. Understanding electron configuration is crucial for predicting an element's chemical, electrical, magnetic, and bonding properties.

The configuration for a neutral atom follows the Aufbau principle, which dictates the sequence in which energy levels and sublevels are filled with electrons. For example, neutral fluorine with an atomic number of 9 has an electron configuration of \(1s^2 2s^2 2p^5\).

When atoms become ions, their electron configuration changes due to the loss or gain of electrons. For cations, electrons are removed starting from the highest energy orbital. Anions, on the other hand, gain electrons in the available lowest energy orbitals. For instance, when the fluorine atom forms the \(\mathrm{F}^{-}\) ion, it gains an electron to complete its \(2p\) orbital, resulting in a configuration of \(1s^2 2s^2 2p^6\), which is isoelectronic with neon, a noble gas. In educational content, providing clear explanations and examples of how ions alter their electron configurations helps students understand periodic trends and ion formation.