By Ron B. Davis Jr., Georgetown University
Except for the noble gases, every other element on the periodic table tries to increase or decrease their count of valence shell electrons to achieve an octet. They interact with other atoms in various ways to do this, many of which result in the phenomenon of chemical bonding. Chemists distinguish three main types of chemical bonds: ionic, metallic, and covalent.
Ionic Bonding
To understand this type of chemical bonding, let’s consider the interaction between sodium and fluorine. Sodium has just one too many electrons. This means that sodium is all too happy to give up a negatively-charged electron. Meanwhile, the fluorine atom is happy to gain that negatively-charged electron.
Fluorene reaches eight valence electrons by adding an electron, and sodium reaches eight valence electrons by losing an electron. And as a result, the two strike a deal—an electron is exchanged from sodium to fluorine. This causes fluorine to become negatively charged, while sodium has become positively charged.
This exchange of electrons has created ions of opposite charge, and we all know that opposite charges attract. In this case, the ‘opposites’ are electrical charges—so we call this an ‘electrostatic attraction’. The electrostatic attraction between sodium ions and fluorine ions causes them to stick together and form a compound.
We call this kind of interaction ‘ionic bonding’ because in the quest for an octet, the complete transfer of one or more electrons from one atom to another atom changes two neutral atoms into two charged ions.
Properties of Ionic Bonding
Ionic bonding can form vast networks of ions attracted to one another, causing them to form crystals—which can be quite strong. These ionic network bonds are why most ionic compounds are solids with very high melting points. Sodium chloride, for example, melts at almost 1500° Fahrenheit, or about 800° Celsius because of its strong network of ionic bonds.
Such crystals are also brittle, because their highly ordered, repeating structure makes them break, rather than bend, when pressure is applied.
Some simple ionic compounds that we encounter almost every day include sodium chloride in our table salt, iron oxide rust, and even the sodium fluoride that is used as an additive in toothpaste and mouthwash to strengthen teeth.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Covalent Bonding
What happens when atoms of elements with similar, or even identical, valence shells encounter one another? Giving or receiving electrons is no longer such an attractive option.
Take the example of two fluorine atoms. Both atoms are itching to gain one more valence electron to complete their octet, but neither is willing to lose an electron to satisfy the other. This results in a situation in which the two fluorine atoms can only be satisfied if they share electrons. By overlapping their valence shells, each fluorine atom can be fooled into thinking that it has hold of an extra electron.
We call this type of bonding covalent bonding because it involves a sharing of valence electrons to satisfy each atom’s octet.
We see this form of chemical bonding mostly between nonmetals from the right side of the table. Covalent bonds hold together discrete molecules of elements like oxygen, nitrogen, chlorine, and bromine. Small molecules like these can be easily separated from one another to produce gas and liquid-phase nonmetal elements. In other cases, we find larger networks of covalently-bonded atoms, as we observe in the solid nonmetal elements sulfur and carbon.
Metallic Bonding
The third type of chemical bonding that we commonly see in nature is known as metallic bonding. Take the example of potassium atoms, which the periodic table predicts would have just a single valence electron. It is going to be difficult—in fact essentially impossible—for an atom of potassium to satisfy an octet sharing electrons with one other atom. They simply don’t have enough to consummate the arrangement.
However, when they combine with other metals, they can find a way to release their claim to their outermost electrons without actually becoming an ion! This is done through our third type of bonding—metallic bonding.
When a large matrix of metal atoms comes together, they can combine their valence shells into one enormous region of space called a valence band. This valence band can theoretically stretch on without limits, and it acts as a superhighway for valence electrons, which are free to move throughout the band. This, in effect, confuses the potassium atoms into thinking that they have lost their outermost electron.
Metallic bonding via one enormous valence band explains why metals are malleable , since rearranging a group of metal atoms does not disrupt the valence band that they enjoy.
And metallic bonding also explains why metals in general are good electrical conductors. When an electrical voltage is applied across a metal, the electrons involved in the metallic bond can flow toward the positive end, resulting in electrical current.
Common Questions about the Different Types of Chemical Bonding
There are three types of chemical bonds: ionic, covalent, and metallic. Ionic bonds are formed when a metal and a nonmetal interact by exchange of electrons; covalent bonds are formed when nonmetal atoms come together to share a few of their valence electrons; and metallic bonding happens when metals interact with one another.
Covalent bonding is a type of chemical bonding that occurs when atoms with similar valence shells interact with one another. In this chemical bonding, atoms share their valence electrons to reach the octet state. Covalent bonding often occurs between the nonmetals from the right side of the periodic table.
Some simple ionic compounds that we encounter almost every day include sodium chloride in our table salt, iron oxide rust, and even the sodium fluoride that is used as an additive in toothpaste and mouthwash to strengthen teeth.
