By Robert M. Hazen, Ph.D., George Mason University
In thinking about ionic bonding, the key is to remember that atoms or molecules with magic numbers of electrons are particularly stable, while atoms or molecules that are one or two electrons too many or too few are unstable. Imagine what would happen if all combinations of electrons had exactly the same energy. In such an event, the world of chemistry would be boring.
Formation of Ionic Bonding
Let’s look at the periodic table. Chlorine, element 17, for example, has one too few electrons. It wants to have 18, but it only has 17. It’ll do almost anything it can to gain that electron. By the same token, sodium, which is element 11, has one too many electrons, and it’s going to do almost anything it can to lose an electron.
So, imagine what happens when a chlorine atom meets a sodium atom. Well, naturally the sodium says, “Here, take my electron. I don’t want it.” And so, the sodium’s happy it has 10; chlorine’s happy, it has 18. And something else happens in the process.
When sodium gives up that electron, it now has 11 positive charges in its nucleus, but only 10 electrons, so it’s a +1 ion. And the chlorine, it has 17 positive charges in its nucleus, but now it has 18 electrons, so it’s a -1 ion. You have a +1 ion, a -1 ion, they see each other and they say, “Ah-ha, electrostatic attraction,” and they bond. This is the formation of an ionic bond.
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Ionic Bonding: Definition and Examples
Indeed, we see this type of ionic bond in many kinds of common materials, for example, sodium chloride or table salt. Whenever you have an alkali metal, like sodium, that meets up with a halogen, like fluorine or chlorine, they form a salt. The positive and negative ions attract each other, and so you get the bond. Now, because these bonds are between two ions, it is called the ionic bond.
And there are many examples from the periodic table. Sodium chloride is the most common example of these, but there are many others. For example, when you buy salt, you’ll often notice that it’s called iodized salt. That’s because we need a small amount of iodine in our diet to help the thyroid gland.
If we don’t get it other ways, we can get it from table salt. Because in addition to having sodium chloride, table salt typically has about 1/100th of a percent of potassium iodine, another one of these alkali halides. And that’s because potassium, in the periodic table, in the first column, bonds with iodine, the halogen, in the next to the last column.
Learn more about phase transformations and chemical reactions.
Quartz, the Most Common Type of Ionic Bonding
Now, one of the most common types of ionic bonding in nature links silicon, which is element 14, and oxygen, element 8. On the periodic table, you’ll see that silicon, element 14, then wants to lose 4 electrons, become a +4 ion, while oxygen, element 8, wants to gain two electrons and become a -2 ion, forming a strong ionic bond between one silicon and two oxygens which is SiO2.
This ionic Si-O bond is particularly strong because it links a +4 ion with a -2 ion. Now, remember Coulomb’s law which describes the force, the electrostatic force between two charges. The force is proportional to the product of the charge in the first object and the charge in the second object. In silicon-oxygen bonding, the relative strength is 4 times 2, or 8. So, for a given separation of ions, the silicon-oxygen bond is eight times stronger, making a very strong and resistant material.
Strong Si-O bonds are extremely common in nature. They form, for example, the mineral quartz, SiO2, which forms beautiful crystals. These are the power crystals you may have heard about. But quartz forms beach sand, and sand grains are typically grains of quartz. Si-O bonds also form window glass.
Learn more about the states of matter.
Distinctive Properties
Now, as you might expect, the distinctive character of ionic bonds leads to distinctive properties, and you can look at three of these kinds of properties: strength, transparency, and electrical conductivity. Ionic bonds feature very strong and directional bonds.
Now you can think of these bonds as rigid sticks—like Tinker toys—that if bent too far, they’re going to break. You can see this anytime you’ve ever dropped a ceramic mug or a cup. If you take a cup and drop it on the floor, it smashes into tiny pieces.
But those pieces retain their original shape because of the rigid bonding. And, in fact, if you take the cup and the fragments, you can actually often glue those pieces back together and use the cup again. This is because ionically bonded materials are both strong and brittle.
Now let’s talk about optical properties. Light waves scatter off materials because of their electrons. In ionic bonding, all the electrons are tightly locked to one atom or another, so there are not a lot of free electrons around to scatter light. As a result, many ionically bonded materials are transparent. Window glass, for example, the mineral quartz and many others, are transparent to light—a feature of ionic bonding.
Common Questions about Ionic Bonding in Chemistry
In ionic bonding, electrons are transferred from one atom to another, resulting in the formation of positive and negative ions. It’s the attraction created between positive and negative ions that creates a compound.
There are many examples of ionic bonding in nature. Table salt is an excellent example of an ionic bond between sodium and chlorine. Silicon and oxygen also bond with a strong ionic bond to form quartz. It should be noted that the beach sand is made of quartz.
Ionic bonding has three unique properties. These features include high resistance, electrical insulation, and transparency.
