About this video
This video extends electron configurations to ions. It works out fluorine (1s2 2s2 2p5) and shows that the fluoride anion gains one electron into the 2p sub-shell (2p6), then shows that a calcium 2+ cation loses its two 4s electrons, leaving the same configuration as argon.
You'll be able to
- write the electron configuration of a neutral atom and use it to find the configuration of its ion.
- explain that an anion has extra electrons added to the next available space and a cation loses its highest energy electrons.
- use noble gas notation to show that some ions have the same configuration as a noble gas.
Key words
- ion
- An atom that has gained or lost electrons, so it has an overall electric charge.
- anion
- A negatively charged ion, formed when an atom gains one or more electrons, like fluoride.
- cation
- A positively charged ion, formed when an atom loses one or more electrons, like calcium 2+.
- electron configuration
- A description of how an atom's or ion's electrons are arranged in shells and sub-shells, such as 1s2 2s2 2p5.
- noble gas configuration
- A shorthand that writes the previous noble gas in place of its electrons, e.g. calcium is argon plus 4s2.
Transcript
- [Instructor] In many videos we have already talked about electron configuration and now in this video we're going to extend that understanding by thinking about the electron configuration of ions. These are going to be charged atoms. Let's just start looking at some examples.
Let's say we are dealing with fluorine. Now, we know what a neutral fluorine atom's electron configuration would be. In fact, if you want a little bit of practice, try to pause this video and think about what is the electron configuration of a neutral fluorine atom?
All right, now let's work through this together. A neutral fluorine atom has nine electrons, and we could just use our Periodic Table of Elements. So first, we're going to have two electrons in 1s. So we'll have 1s two. And then we're going to go to the second shell.
So then we go to 2s two. So far we have filled in four electrons. And next we got to the 2p sub-shell. And we are going to have, we're talking about a neutral fluorine, we are going to have one two three four five electrons in that 2p sub-shell. So it's 2p five.
So if that's the electron configuration for fluorine, what do you think the electron configuration for fluoride would be? This is just the anion that has one extra electron. It is a negatively charged ion. Pause this video and try to figure it out. Well, here you're now going to have one extra electron.
The fluorine has nabbed an electron from someplace and so where will that extra electron go? Well our 2p sub-shell has space for one more electron. So that's where it will go. So the fluoride anion is going to have an electron configuration of 1s two, 2s two, 2p, now it's going to have an extra electron here, 2p six.
2p six. Now let's do another example. Let's say we wanted to figure out the electron configuration of a part positively charged calcium ion. So calcium, let's make it two plus. It has a positive charge of two. You could do this as a neutral calcium that has lost two electrons.
What would be its electron configuration? Pause this video and try to figure that out. All right, well one way to figure this out is first we could figure out the electron configuration of a neutral calcium atom and then from that, we can take two of the highest energy electrons away.
And so neutral calcium, you could view it, actually let's do it in noble gas configuration. Neutral calcium, the noble gas that comes right before calcium is argon. So it's going to have the electron configuration of argon and then we are going to have two electrons for that fourth shell.
It's going to fill in the 4s sub-shell. And so we're going to have argon and then we're going to have, let me do this in a new color, let's call this 4s two. Now what do you think is going to happen if we were to lose two electrons? Well those two electrons in that 4s sub-shell, in the fourth shell, are gonna go away.
And so the electron configuration here for calcium with a positive two charge, this calcium cation, is going to be the electron configuration of argon and no 4s two. So it's actually going to have the exact same electron configuration as argon. So I will leave you there, just a couple of examples.
And I encourage you, if you're in the mood, just pick any of these atoms, any of these elements, and think about what would happen if they gained or lost an electron and what their electron configurations might be.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.