Explain the difference between the charge of an ion, such as a charge of 2- for an O2- ion, and the oxidation state of an atom, such as the -4 oxidation state of carbon in CH4.

Ion charge is a fundamental concept in chemistry that refers to the electric charge of an ion. An ion is an atom or group of atoms that has lost or gained electrons, resulting in a net charge. This can happen through various processes, such as the transfer of electrons during the formation of ionic bonds. For example, in an oxygen ion with the notation O2-, it has gained two extra electrons, hence the charge is 2-. Understanding the ion charge is critical when it comes to predicting the composition of compounds and their reactions.

The charge of an ion directly influences how it interacts with other ions and molecules around it. Ions with opposite charges are attracted to each other and can form stable ionic compounds. This process is driven by the pursuit of a stable electronic configuration, often resembling the filled electron shells of noble gases.

Oxidation states are slightly more abstract than ion charges. They denote the effective charge on an atom within a compound, assuming that all the bonding electrons are assigned to the more electronegative atom. Oxidation states are vital in redox reactions where electron transfer occurs and help chemists keep track of these changes. For instance, in methane (CH4), the carbon atom is assigned an oxidation state of -4. This does not mean the carbon actually has a charge of -4; rather, it is a way of expressing that carbon has effectively received eight electrons from four hydrogen atoms.

Even though most bonds are not entirely ionic—and thus the oxidation state is a conceptual charge rather than an actual physical charge—it's a valuable tool in understanding the electron transfer during chemical reactions and in balancing redox equations.

Electronic configuration describes the arrangement of electrons in an atom or molecule. It is defined by the specific orbits, or shells, in which electrons reside, as well as by the subshells and orbital types they fill according to quantum mechanics. For instance, a neutral oxygen atom has an electron configuration of 1s² 2s² 2p⁴, indicating two electrons in its innermost shell and six electrons in its second shell, with the p subshell not being fully occupied.

When an oxygen atom becomes the O2- ion, it gains two additional electrons, resulting in a filled 2p subshell. This information is critical for predicting and explaining the chemical behavior of atoms, such as their reactivity, bonding abilities, and the formation of ions. The drive for a stable electronic configuration is often the reason an atom will lose or gain electrons to form an ion in the first place.

Ionic bonds are the electrostatic forces of attraction that hold together ions with opposite charges in a compound. These bonds are formed when an electron is transferred from one atom to another, resulting in the creation of positively charged cations and negatively charged anions. Taking the example of sodium chloride (NaCl), sodium (Na) donates one electron to chlorine (Cl), forming Na+ and Cl- ions. The resultant bond between these oppositely charged ions is ionic.

Ionic bonds are generally found in salts and are responsible for many of their properties, such as high melting and boiling points, and the ability to conduct electricity when molten or dissolved in water. Understanding ionic bonds is essential for grasping the structure and properties of various substances, as it is one of the primary types of chemical bonds that hold compounds together.