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Jump to one of the following inorganic nomenclature parts:   Choose One Introduction to Inorganic Nomenclature Part 1- Molecular Compounds Part 2- Monatomic Ions Part 3- The Stock System Part 4- Polyatomic Ions Part 5- Ionic Compounds Part 6- Binary Acids and Oxoacids Part 7- Quizzes

Let's first make sure we understand the word "ion". Elements in the Periodic Table have a nucleus with particles called protons and neutrons in it. The protons have a positive charge associated with them and neutrons have no charge (neutral). Surrounding an element's nucleus is a cloud of one or more electrons and these electrons have a negative charge. Since an element does not have a net charge, it must have just as many electrons as there are protons. Most elements can make an ion which results from a difference between the number of protons and electrons. Since changing the number of protons changes the element, it must be the number of electrons that is changing. If it has more electrons than protons it has more negative charge than positive charge and thus it's a negative ion. Otherwise called an anion. Likewise, if it has less electrons than protons it has a net positive charge and is called a cation (pronounced "cat"-ion). All we're dealing with for the moment are single-atom ions or monatomic ions. Monatomic comes from monoatomic with the o dropped).

How do you tell if an element can be made into an anion or a cation? In other words, if an element can be turned into an ion, does it tend to gain electrons and thus become an anion or does it tend to lose electrons and thus become a cation?

Elements to the left in the Periodic Table tend to lose electrons and become cations while elements in the right of the Periodic Table tend to gain electrons and become anions. So, group IA, IIA, and metals in IIIA will lose electrons (cations) while the group VA, VIA, and VIIA nonmetals tend to gain electrons (anions). How many? That has to do with the elements position in the Periodic Table with respect to its nearest noble gas. The noble gases, group VIIIA, are special and they tend to neither lose nor gain electrons. More in just a minute about how we decide just how many electrons an atom gains or loses to become an ion.

With so much to worry about, here's a simple statement to remember that should help you-

Metals tend to react by losing electrons.

Ah, so metals tend to make positive ions (cations) while nonmetals and metalloids tend to make negative ions (anions). I know this is a very simplistic answer and that I'm essentially saying "trust me". This will be explained after learning how to write electron configurations and discussing topics like ionization energy and electron affinity.

Which brings up another problem. Just what the heck is the charge on an ion? As stated above, special emphasis was placed on group VIIIA (the noble gases). For reasons that will be explained later, many elements tend to have electronic configurations analagous to the nearest noble gas. For right now we'll just show the Periodic Table but we'll quickly do some things with it-

Cations of Group IA, IIA, and IIIA:

Here are the group 1a elements.

Lithium is in group 1A and removing 1 electron would give it an electron configuration analogous to that of helium. It would then have 3 protons and 2 electrons which would give a charge difference of 1+ for the ion. Any ion of group 1A would have the same charge. Sodium: 1+, potassium: 1+, etc. You may be wondering why I've chosen to exclude hydrogen. It's not because it doesn't have a corresponding ion (it does); but, it is because it doesn't make traditional ionic compounds. For the moment you'll just have to stick with this simplistic explanation because I don't wish to go into detail at this time. I don't want to overwhelm you with information.

Here are the group 2a elements.

Similarly, magnesium can lose 2 electrons and we'll get the ion with a charge of 2+. Same reasoning goes for the rest of group 2A. As I did with hydrogen, I'm also leaving out beryllium for the time being.

Here are the group 3a elements.

And similarly for the both group IIIB and the metals in group IIIA. These lose 3 electrons to form ions with a charge of 3+.

Now, how do we go about writing the symbol and the name for the resulting ions? The first thing is to write the symbol for the element. The symbol for sodium is Na, that for magnesium is Mg, etc. Next, you need to indicate the charge. If there isn't one indicated then it's assumed to be 0. While I consider the following to all be equivalent- Na⁺, Na⁺¹, and Na¹⁺, the proper way to write an ion is Na¹⁺ (number followed by charge). The same method will be used for writing negative ion symbols.

And now the names. The names for positive ions, cations, are very simple. You just have to tack on "ion" at the end. Na¹⁺ is the sodium ion. Mg²⁺ is the magnesium ion. Sc³⁺ is the scandium ion and Al³⁺ is the aluminum ion.

Now might be a good time to jump to the quizzes page and try quizzes 3 and 4.

Anions From Nonmetals:

Here are the nonmetals.

The negative ions, anions, are done much the same. Adding an electron to fluorine creates a singly-charged negative ion. Adding 2 electrons to oxygen creates a doubly-charged negative ion. And adding 3 electrons to nitrogen creates a triply-charged negative ion. Or, F^1-, O^2-, and N^3-. Perhaps you've noticed from looking at the Periodic Table that there's only been mention of the nonmetals for making anions and nothing about the metalloids or the metals. If so, you're right. The metals (of which we've only talked about groups IA, IIA, IIIA, and IIIB) form cations and the nonmetals form anions. That leaves only 9 elements for anions- fluorine, chlorine, bromine, iodine, oxygen, sulfur, selenium, nitrogen, and phosphorus. Carbon is sometimes mentioned and while is does make a C^4- ion, it generally forms covalent bonds and that's why I've left it out.

While the symbols for anions are the same format as those for cations, the naming is a bit different. The anions' names use a modified form of the element name with "ion" again tagged at the end just as was done for the second element in molecular compounds. The last few letters of the element name are lopped off and replaced with "ide". Let's make a table for the possible monatomic ions-

Unlike molecular compounds, we're only looking at nonmetals as anions and not metalloids. We'll only use metalloids in molecular compounds to simplify the naming rules.

Now might be a good time to jump to the quizzes page and try quizzes 5 and 6.