Electron Configurations. The purpose of this tutorial is to help you understand how electrons are arranged in their energy levels. You will learn how to write electron configurations, and how these electron arrangements relate to the shape and lay-out of the periodic table. Because electrons are so important in chemistry, the way in which they are arranged around the nucleus plays a crucial role in determining the chemical reactivity of all the elements.
Transcript
Electron Configurations.The purpose of this tutorial is to help you understand how electrons are arranged in their energy levels. You will learn how to write electron configurations, and how these electron arrangements relate to the shape and lay-out of the periodic table. Because electrons are so important in chemistry, the way in which they are arranged around the nucleus plays a crucial role in determining the chemical reactivity of all the elements.
First let’s review a little: As we have learned, electrons exist in very specific energy levels. And when these electrons absorb energy…They get energized up to higher levels. Actually, the jump to higher levels is not a gradual transition as was just shown.
It is a “quantum” jump, and looks more like this:
Quantum means it happens all at once – instantaneously – because the electron can never exist between levels – not even for a second.
Once it is at this higher level (excited state), it doesn’t stay there long. It quickly drops down to a lower level – again as a quantum leap – and as it does, it gives off a distinct band of light energy.Also, notice how the electron doesn’t have to drop all the way back down to the lowest level. It can get energized up to any level, and from there it can drop to any lower level. AND the different drops each produce different frequencies of light.
See how an electron dropping from the 3rd level to the 2nd level produced red lightA 4 2 electron drop produces blue lightAnd a 5 2 drop produces violet light
1st
2nd
3rd
4th
5th
6th
7th
2p
Now let’s take a closer look at these electron energy levels. We’ll color code them to make them easier to distinguish...We will see in a moment that these levels are actually made up of sublevels. The higher up you go, the more sublevels there are. We will represent these sublevels as lines with boxes on them.The boxes represent the “orbitals” that make up the sublevels. This is where the electrons hang out. A maximum of two electrons can fit in any orbital. The sublevel shown below is part of the 2nd level and it is called the “2p sublevel.”
Note that the 2p sublevel is made up of 3 orbitals (see the three boxes). And since two electrons can fit in each orbital, the 2p sublevel is capable of holding a maximum of six electrons:
Also, let’s not forget about the nucleus… It is positively charged (because of all the protons in it).
+
After all, it is this positively charged nucleus that holds the negatively charged electrons around it in the first place.
7s7p7d7f7g7h7i
1s
2s2p
3s3p
4s
3d
4p4d4f
5s5p5d5f5g
6s6p6d6f6g6h
1st
2nd
3rd
4th
5th
6th
7th
So let’s start at the bottom. The 1st energy level is comprised of just one sublevel: It is called the 1s sublevel, and it contains just one orbital. That’s it!
The 2nd level is made up of 2 sublevels:The 2s sublevel (which, like the 1s, contains just one orbital), and the 2p sublevel which contains three orbitals.
Any guesses about the 3rd level?The 3rd is made up of 3 sublevels [Do you see the pattern?] The 3s sublevel (1 orbital), the 3p sublevel (3 orbitals) and the 3d sublevel (5 orbitals)
How about the 4th level? You should have a pretty good idea about everything concerning it, accept what the new letter is. Is this what you were thinking? 4s (1), 4p (3), 4d (5), and 4f (7). See how the number of orbitals is always a consecutive odd number?Also notice how the sublevels start to overlap.
The 5th level is just what you would expect:Five sublevels: 5s (1), 5p (3), 5d (5), 5f (7) and 5g (9). But look at how extensive the overlap becomes.
And with the 6th and 7th, it just gets worse and worse!
The 4s is actually a little lower than the 3d. This overlap is very important, and it becomes more extensive as we move to higher levels.
+
7s
7p7d
7f
7g
1s
2s2p3s
3p4s3d4p
4d
4f
5s
5p
5d
5f
5g
6s
6p
6d
6f
6g
6h
1st
2nd
3rd
4th
5th
6th
7th
Now, it may not look like it, but there is a pattern to the levels shown at left, and the order that they go in from lowest energy to highest (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s…)
So let’s look at them again, but let’s spread them out a bit horizontally, so they are not so crowded.
+
1s
2s
3s
4s
5s
6s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
6f5g
6g
7s
7p
7d
8s
8p
7f8d
9s
9p10s
This is the order in which they were just introduced to you…
There are plenty more, but they go off the screen, so we’re not going to worry about them!
+
1s
2s
3s
4s
5s
6s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
6f5g
6g
7s
7p
7d
8s
8p
7f8d
9s
9p10s
1s
2s
3s
4s
5s
6s
7s
8s
9s
10s
2p
3p
4p
5p
6p
7p
8p
9p
3d
4d
5d
6d
7d
8d
9d
4f
5f
6f
7f
8f
9f
5g
6g
7g
8g
9g
6h
7h
8h
9h
10p 10d 10f 10g 10h
But check out this simple table at right. If you draw diagonal arrows starting at the bottom like this…
It shows the precise order in which the energy levels are arranged from lowest to highest!
+
1s
2s
3s
4s
5s
6s
2p
3p
4p
5p
6p
3d
4d
5d
6d
4f
5f
6f5g
6g
7s
7p
7d
8s
8p
7f8d
9s
9p10s
1s
2s
3s
4s
5s
6s
7s
8s
9s
10s
2p
3p
4p
5p
6p
7p
8p
9p
3d
4d
5d
6d
7d
8d
9d
4f
5f
6f
7f
8f
9f
5g
6g
7g
8g
9g
6h
7h
8h
9h
10p 10d 10f 10g 10h
Watch …
+
sp
d
f
1234567
He H
So what does all this have to do with chemistry? Below is a rough sketch of the periodic table. For the sake of this discussion, we are going to move He over so it is in that little open space next to H:And now we are going to number the periods 1 through 7:As you will see, these periods correspond (more or less) to the energy levels we’ve just been discussing. And we are going to designate the four distinct rectangular blocks by the type of sublevel they match up with: “s,” “p,” “d” and “f:”
Now let’s take the first ten sublevels (1s, 2s, 2p…) and see how the electrons filling these sublevels takes us row by row across the periodic table, and allows us to read electron configurations right off the table…
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
And let’s also number the groups within each block (1,2,3,4…)
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1234567
OK, so we’re going to use arrows pointing up or down to represent the electrons. Can you guess into which box the first electron would go given that it is attracted to the nucleus?
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s1
1234567
That’s right: it goes in the 1s sublevel. And its el. config is 1s2. Notice in the table above where H is – in the area designated as 1s. So where does the next electron go?
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
If you were thinking it went in the 2s, then you forgot that each orbital can hold up to two electrons. Note how He is right here in the area designated as 1s2 and so its el. config. is 1s2.+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Now that the 1s is filled, the next electron goes in the next sublevel – the 2s. Again note how Li is in 2s1.
Its full el. conf. is 1s2 2s1. What is Be’s el. conf?+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Is this what you were thinking? Good. Now look at the periodic table above, what comes after the 2s sublevel?
The 2p sublevel. So what will the next el. conf. be?+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Is this what you were thinking? Notice how B is in the 2p1 spot.
So its full el. conf. is 1s2 2s2 2p1. What’s next?+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Is this what you were thinking? Notice how C is in the 2p2 spot. So its el. conf. is 1s2 2s2 2p2
Notice also how when we fill a sublevel…+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p3
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
…we put one electron in each orbital until the sublevel is half filled…
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p4
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
… and then we go back and start pairing off
This is called “Hund’s Rule, but it also referred to as the bus seat rule. Can you figure out why?+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p5
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Look at F. It’s just one electron away from having filled 2p sublevel…
And it’s just one square away from the end of the 2p block.+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
And then Ne has a completely filled outer level. Na is next. Can you guess where the next electron is going to go?+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
That’s right: in the 3s sublevel. Right now, write down in your notebook what you think the next three el configs will be. +
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Did you get this one right?
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
How about Al’s? See how Al is in the 3p1 spot on the per table
and its el config ends with 3p1+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Now just advance through the next 23 slides, but as you do, make sure you are understanding+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p3
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Exactly what is going on… how the el configs simply follow the sequence of the periodic table.+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p4
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
Your goal by the end of this slide show is to be able to write el configs for any element using just the periodic table – and your brain!+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p5
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d3
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d4
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d5
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d6
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d7
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d8
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d9
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
5s
+
1s
2s
3s
4s
2p
3p
4p
3d
4d5s
sp
d
f
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1
1234567
1 2
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6
+
1s2
2s2
3s2
4s2
5s2
6s2
7s2
2p6
3p6
4p6
5p6
6p6
3d10
4d10
5d10
6d10
4f14
5f14
1
2
3
4
5
6
7
So, the pattern for reading the electron configurations right off the periodic table is this:If you are wanting to write the electron configuration for any element, just follow this pattern and remember to stop at the element you’re representing.
1s2
2s2
3s2
2p6
3p5
1
2
3
4
5
6
7
For example, Cl (#17) which is right here on the table:
By the way, the orbitals are not really little empty boxes on a line:
2p
Instead, they are specific three-dimensional shapes called probability clouds that show where you are most likely to find the electron around the nucleus. The s sublevels are all spherical in shape:And they just get larger and larger as you move to higher levels
1s2s3s
The p orbitals are a bit more complicated.They are peanut shaped! And within the 2p sublevel, the three orbitals are oriented at right angles to each other. They are referred to as the 2px, 2py and 2pz orbitals.And they fit together around the nucleus like this:
Now try some of the problems from the Electron Configuartion worksheet.
