What is an ion?

 Ions 101 – If you’re like me and avoided chemistry like the plague

 Let’s back up and start at the beginning. What is an atom? Assuming you have a basic idea of that, let’s review some atomic basics.

1)      Neutrons:  Neutrons are uncharged particles that are found in the center of the atom (the nucleus). Neutrons give mass (weight) to the atom but do not participate in chemical reactions.

 2)      Protons: Protons are positively charged particles that are also found in the nucleus. Like neutrons, protons give mass to the atom but do not participate in chemical reactions. The number of protons an atom has is called the atom’s atomic number, and determines the atom’s identity (e.g. carbon atoms have 6 protons, oxygen atoms have 8 protons).

3)      Electrons: Electrons are negatively charged particles that are found in electron shells surrounding the nucleus. They have essentially no mass but are important in chemical reactions. The first electron shell can hold 2 electrons. For most biologically relevant atoms, additional electron shells (if present) can hold up to eight electrons.

Each atom contains equal numbers of protons and electrons. The number of neutrons may vary within atoms of a particular type. (For example, carbon atoms may have 6, 7, or 8 neutrons). Atoms that vary only in the number of neutrons are called isotopes.

Atomic stability:

 The stability of atoms depends on whether or not their outer-most shell is filled with electrons.  If the outer shell is filled, the atom is stable.  Atoms with unfilled outer shells are unstable, and will usually form chemical bonds with other atoms to achieve stability.

 This isn’t a value judgement! We need unstable atoms because they make molecules. No molecules = no bueno, because you and I, my friend, are made up of lots and lots of molecules. And every single element, thing, strand of hair, particle, crumb of toast, is made up of molecules too.

 The two types of chemical bonds that atoms can form to achieve stability are called ionic bonds and covalent bonds. In ionic bonds, atoms donate or receive electrons to achieve stability. In covalent bonds, atoms share electrons to achieve stability. The type(s) of bond a particular atom can form depends on the numbers of electrons in their outer shells.

 Ionic Bonds

When an atom or molecule loses or gains one or more electrons, we call it an ion. If it loses an electron (net gain of charge because an electron carries a negative charge) we call it a cation, when it gains an electron we call it an anion. A cation is typically a metal, but hydrogen is also a cation. An anion is typically non-metal. But as in all things, there will be exceptions so don’t quote that in your term paper.

 By the way: An atom (rather than a molecule) that loses or gains electrons is called a monatomic ion.

 Confusing? Think of it like you are just adding or subtracting a negative number or a positive number to an existing number.

Both positive and negative ions are created in nature every day. They have very different effects on the human body, however.