Chemical Bonds II: Ionic

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  • 0:14 Valence
  • 1:45 Ionic Bond
  • 4:44 Bond Strength
  • 5:41 Summary
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Lesson Transcript
Instructor: Greg Chin
Did you know that the scientific name for table salt is sodium chloride? Find out how sodium and chlorine atoms come together to form your favorite seasoning.

Diagram of a chlorine atom
Chlorine Atom

We've already learned that atoms with an incomplete valence level are unstable. We've learned that there are various ways than an atom can deal with this sort of instability. We've already talked about how atoms can share electrons. So, by sharing valence electrons, they can complete their valence level.

Another way that atoms can deal with an incomplete valence level is they can take or donate electrons. We can predict how atoms will behave based on their electronegativity. So, the electronegativity of an atom will determine whether sharing, taking or donating is going to be the best strategy for that atom.

Let's talk about chlorine. So, chlorine is an atom that has seven valence electrons.

If we know that atoms want to have eight valence electrons in the outer shell here, we can predict that it would be easier for chlorine to just take an electron. It's one electron away from having a complete shell.

On the other hand we have sodium here, and sodium has just a single valence electron in its outer shell.

Diagram of a sodium atom
Sodium Atom

Again, with the idea of having eight electrons in the outer shell, it's going to be easier for sodium to just get rid of this single valence electron. What we can see here is that we have two perfect partners; one wants to get rid of it, and one wants an extra electron. If sodium gives its extra electron to chlorine, both of them are going to be a lot happier.

If sodium give its electron to chlorine, it empties its outer shell. What was formerly its valence shell is now gone, so this shell disappears and reveals a shell underneath that now has eight electrons. These eight electrons complete the shell for sodium, and it's now more stable. By the same token, chlorine, because it added that extra electron, has filled its outer shell. So, it's also more stable. Both of the two atoms have increased their stability by making this electron exchange.

In this process we've created a scenario where there are more protons than electrons in sodium and there are more electrons than protons in chlorine. What that means is - if we remember that protons have a positive charge and electrons have a negative charge - I've created a sodium atom that has a positive charge. When we have a charged atom, we call that an ion. In particular, a positively charged ion is called a cation. By the same token, I've also created a situation where we have a chlorine atom that has a negative charge. This is also an ion. It has a negative charge, so it's called an anion.

Stable chlorine and sodium atoms
Chemical Bond

Because we have two ions that have opposite charges, they're going to attract each other. These two atoms are going to move toward each other, and we're going to create a bond between these two atoms because of the electrostatic charge that's bringing the two of them together. When these two ions come together, they form an ionic bond.

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