In this lesson we're going to talk about ionic bonds, covalent bonds, particularly polar covalent bonds and non-polar covalent bonds. So let's say if we have this bond, the bond between two hydrogen atoms. Would you describe this bond as ionic, polar covalent, or non-polar covalent?
Anytime you have a bond between two atoms of the same element, it's always going to be a non-polar covalent bond. Now the reason why it's a covalent bond is because the electrons in this bond are shared equally due to the fact that we have the same atom, I mean the same type of atom, and so therefore they have the same electronegativity and so they pull on those electrons with an equal force. So because the electrons are shared equally in this molecule, it's going to be a nonpolar covalent bond. Now here's another example for you.
What about the carbon-oxygen bond? Would you describe it as ionic or covalent? Now, anytime you have a bond between two nonmetals, typically it's usually a covalent bond.
So we need to determine if it's a polar covalent bond or a nonpolar covalent bond. And we need to look at the electronegativity values of these two elements. So here are some numbers that you want to be familiar with.
Hydrogen has an electronegativity value of 2.1. Boron is about... let me list out the elements... Boron, Carbon, Nitrogen, Oxygen, and Fluorine. So Boron is about 2.0.
Carbon is 2.5. N is 3.0. O is 3.5.
F is 4.0. And these values are based on the textbook I'm using. Some textbooks might have slightly different values but you want to use the values based on the textbook you're using.
So carbon has an electronegativity value of 2.5 and oxygen has a value of 3.5. If the electronegativity difference is.5 or more than the bond is said to be polar. If the electronegativity difference is 0.4 or less, then the bond is said to be nonpolar. So 3.5 minus 2.5, that's 1. So therefore, we can say that the carbon-oxygen bond is a polar covalent bond.
The electrons are being shared, but not equally. Now, because oxygen is more electronegative than carbon, it's going to have a partial negative charge. And carbon, because it's less electronegative than oxygen, it has a partial positive charge.
So how can we indicate bond polarity? How can we show the dipole moment in this bond? You need to draw an arrow pointing towards the more electronegative element.
And so whenever you see a dipole moment like this, it tells you that this bond is a polar bond. Now what about the bond between sodium and chlorine? Would you describe it as ionic, polycovalent, or non-polycovalent? Sodium is a metal. Chlorine is a non-metal.
And typically, when you have a metal mixed with a non-metal, for the most part, it's safe to say that it's going to be an ionic bond. Sodium chloride is made up of ions. In this substance, sodium has a positive charge and chlorine has a negative charge.
Positively charged ions are known as cations and negatively charged ions are known as anions. And so that's why we have an ionic bond. We know that opposite charges attract and so there is an electrostatic force of attraction that keeps these ions held together and that makes the ionic bond. So typically, whenever you have a metal mixed with a non-metal, ionic interactions are usually created.
Now it's important to understand the difference between an ionic bond and a covalent bond. In a covalent bond, the electrons are shared. In an ionic bond, the electrons are transferred. So in a polar covalent bond, they're shared unequally, but in a non-polar covalent bond, the electrons are shared equally.
Sodium has 11 electrons but it has one valence electron. Chlorine has seven valence electrons. So when you put together, let me draw this differently, an atom of chlorine and sodium, sodium, it's going to give away its one valence electron to chlorine. And when it loses that electron, it acquires a positive charge.
When chlorine accepts it, it's going to have eight valence electrons, and so it's going to be negatively charged, since it gained. an extra electron. So after this transfer of electrons, there's going to be an electrostatic force of attraction that holds these ions together. And so that makes up the ionic bond. Now let's talk about the hydrogen atoms that make up the H2 bond.
Let's say if we have two individual atomic hydrogen particles. both of which contain one valence electron. When these two get together, they will each give up their valence electron to form a covalent bond. And so the two electrons represented by that bond are shared equally among those hydrogen atoms, and that's why it's a non-polar covalent bond. The electrons are shared.
In an ionic bond, you had a transfer of electrons. Sodium gave up an electron, chlorine accepted it. But here, Both hydrogen atoms contributed an electron to create this covalent bond.
And so that's why it's not ionic, but it's covalent. You have a sharing of electrons as opposed to a transfer of electrons. Now let's go through some more examples. So what about the carbon-hydrogen bond? Would you describe it as ionic, polar covalent, or non-polar covalent?
Now carbon has an electronegativity value of 2.5 and for hydrogen it's 2.1. So the electronegativity difference is 0.4, which means that this bond is nonpolar. Whenever you see a molecule that contains only carbon and hydrogen bonds, it's a nonpolar molecule.
For example, methane is nonpolar. It doesn't mix with water. Or hexane. C6H12, that's a nonpolar molecule.
They don't dissolve in polar substances like water or like alcohol. Now what about the carbon-carbon bond? Is it ionic or is it covalent?
Now, both substances have the same electronegativity value, so the EN difference is 0. which means that it's non-polar. So anytime you have two of the same type of atoms that make up a bond, it's always going to be a non-polar bond. The electrons will be shared equally. Now what about the OH bond? What can we say about it?
Is it an ionic bond, a polar covalent bond, or a non-polar covalent bond? Well, let's start with the electronegativity values. Oxygen has an electronegativity of 3.5, and for hydrogen it's 2.1. So the electronegativity difference is 1.4.
So this bond is highly polar. Now, it's a special type of polar bond. Anytime you see hydrogen directly attached with nitrogen, oxygen, or fluorine, it's a special type of bond. Do you remember what it is? It's known as hydrogen bonding.
These are very powerful intermolecular forces. Because of hydrogen bonding, water has a very high boiling point for being a molecule. Most molecules have low boiling points, but those with hydrogen bonds, they have relatively high boiling points.
So we have a polar covalent bond with a special case of hydrogen bonding. Now let's indicate the bond polarity. Because oxygen is more electronegative, it's going to have the partial negative charge. And hydrogen is going to have the partial positive charge.
So to indicate the dipole moment, we're going to draw the arrow towards the more electronegative element. Now let's consider one more example. What about the bond between lithium and fluorine? Would you say it's an ionic?
bond covalent bond, and if it's covalent, is it polar covalent or nonpolar covalent? Lithium is a metal, fluorine is a nonmetal. So automatically, just by identifying the type of element that we're dealing with, we know it's going to be an ionic bond.
The electronegativity difference between lithium and fluorine is huge, but for the most part, if you have a metal and a nonmetal, it's safe to say that you have an ionic interaction. Lithium is a positively charged cation and fluoride is a negatively charged anion.