Give the number of protons and electrons in each of the following common ions: \(\mathrm{K}^{+}, \mathrm{Mg}^{2+}, \mathrm{Fe}^{3+}, \mathrm{Br}^{-},\) \(\mathrm{Mn}^{2+}, \mathrm{C}^{4-}, \mathrm{Cu}^{2+}\)

The atomic number is a fundamental property of an element, indicating the number of protons in the nucleus of an atom. In the periodic table, elements are arranged in order of increasing atomic number, which also dictates the element's unique identity. For instance, Potassium (K) has an atomic number of 19, which means every atom of Potassium contains 19 protons. Understanding the atomic number is crucial for identifying an element and determining its position in the periodic table.

When dealing with ions, the atomic number remains unchanged because it reflects the number of protons, which are unaffected by the process of ionization. The atomic number is invariant for a given element; whether that element is in its neutral form or as an ion.

The periodic table is the tabular arrangement of all known chemical elements, organized by their atomic number, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number, and the table layout shows patterns in elemental characteristics. For instance, elements in the same column, or group, typically have similar properties and ion charges.

The periodic table serves as a guide to understanding the behavior of atoms during chemical reactions, including ion formation. Familiarity with the table allows one to quickly ascertain an element’s atomic number and typical ion charge, aiding in exercises involving the calculation of electron counts in ions.

An ion is an atom or molecule that has gained or lost electrons and thus carries an electric charge. Positively charged ions, called cations, result from an atom losing electrons, while negatively charged ions, anions, result from an atom gaining electrons. The ion charge is denoted by a plus (+) or minus (-) sign along with the number of electrons lost or gained.

For example, a Potassium ion with a charge of +1 (K+) indicates that it has lost one electron, whereas a Bromine ion with a charge of -1 (Br-) has gained one electron. This charge is essential for determining the electron count in ions, which significantly influences the ion's chemical properties and reactivity.

The electron count in ions differs from that in neutral atoms due to the loss or gain of electrons, which creates an ion charge. To find the electron count in an ion, one must know the atomic number of the element—which provides the number of protons—and the ion's charge. For an ion with a positive charge, electrons are subtracted from the atomic number; conversely, for an ion with a negative charge, electrons are added.

As an example, Magnesium (Mg) has an atomic number of 12 and typically forms a 2+ ion (Mg²⁺), indicating it has lost two electrons, giving it a total electron count of 10. This principle is essential when predicting ionic bonds and the resulting chemical behavior of the ions.

The proton count in an atom directly corresponds to its atomic number and is intrinsically tied to the identity of the element. Protons are positively charged particles found in the nucleus of an atom, and their number remains consistent regardless of any changes in the electron count when atoms form ions. For each element on the periodic table, the proton count is constant; this is what fundamentally differentiates one element from another.

In every instance, even when an atom becomes an ion, the proton count does not change. For example, the Iron (Fe) atom has an atomic number of 26, signifying 26 protons, and as an Fe³⁺ ion, it still retains all 26 protons while its electron count is altered due to the charge.