An atom is the fundamental building block of matter, and its structure dictates the chemical behavior of an element. A neutral atom is defined by a central nucleus surrounded by negatively charged electrons. When an atom gains or loses electrical charge, it becomes an ion. Does the process that creates an ion also change the number of neutrons in its nucleus? Understanding the nature of subatomic particles provides a clear answer about the neutron count when a neutral atom like lithium transitions into its ionic form.
The Components of an Atom
Every atom is composed of three primary subatomic particles: protons, neutrons, and electrons. Protons carry a positive electrical charge, and their number determines the atomic number, which identifies the element. Neutrons are electrically neutral and reside alongside protons in the atom’s central nucleus, contributing significantly to the atom’s overall mass. The total number of protons and neutrons in the nucleus is known as the mass number.
Electrons carry a negative charge equal in magnitude to the proton’s positive charge. Electrons orbit the nucleus in specific energy levels or shells. In a neutral atom, the number of electrons equals the number of protons, resulting in a net electrical charge of zero.
How Ions Are Formed
Ions are atoms that possess a net electrical charge because their total number of electrons is unequal to their total number of protons. The process of creating an ion, known as ionization, occurs through the gain or loss of electrons from the atom’s outermost energy shells. When an atom loses one or more electrons, it results in a net positive charge, forming a positively charged ion called a cation. The loss of an electron means the number of protons now exceeds the number of electrons.
Conversely, if an atom gains an electron, it acquires a net negative charge, becoming a negatively charged ion known as an anion. Ionization is a chemical process that affects only the electron cloud, the external part of the atom. This process does not involve the nucleus, meaning the number of protons and neutrons remains unchanged between the neutral atom and its ion.
Lithium: Atom, Ion, and Isotope
A neutral lithium (Li) atom always has three protons, as this number defines it as lithium. The most common form of lithium is Lithium-7, which contains four neutrons in its nucleus, giving it a mass number of seven. The neutral Lithium-7 atom will therefore have three electrons to balance the three protons.
Lithium readily forms a positive ion, Li+, by losing its single outermost electron. The resulting Li+ ion still contains the defining three protons and four neutrons in its nucleus. The only difference is that the ion now has two electrons instead of three, resulting in a +1 charge. This confirms that the number of neutrons is the same in a Lithium-7 atom and a Lithium-7 ion.
It is important not to confuse ionization with isotopes, which are atoms of the same element that have different numbers of neutrons. For instance, Lithium-6 is a stable isotope containing three neutrons instead of four. A neutral Lithium-6 atom has three protons and three neutrons, and its corresponding ion, Li+, would also have three protons and three neutrons, demonstrating that neutron count is constant during ionization, but variable between isotopes.