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**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.

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**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.

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**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. And a 5 2 drop produces violet light See how an electron dropping from the 3rd level to the 2nd level produced red light A 4 2 electron drop produces blue light

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**Now let’s take a closer look at these electron energy levels**

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. 1st 2nd 3rd 4th 5th 6th 7th 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: 2p It is positively charged (because of all the protons in it). Also, let’s not forget about the nucleus… After all, it is this positively charged nucleus that holds the negatively charged electrons around it in the first place. +

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**+ 7i 7th 7h 7p 7s 7d 7g 7f 6th 6h 6p 6s 6g 6f 6d 5th 5d 5s 5g 5p 5f**

And with the 6th and 7th, it just gets worse and worse! The 5th level is just what you would expect: 7i 7th 7h 7p 7s 7d 7g 7f Five sublevels: 5s (1), 5p (3), 5d (5), 5f (7) and 5g (9). But look at how extensive the overlap becomes. 6th 6h 6p 6s 6g 6f 6d How about the 4th level? You should have a pretty good idea about everything concerning it, accept what the new letter is. 5th 5d 5s 5g 5p 5f 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. 4th 4d 4f 4s 4p 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. Any guesses about the 3rd level? 3rd 3s 3p 3d 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) The 2nd level is made up of 2 sublevels: 2nd 2s 2p The 2s sublevel (which, like the 1s, contains just one orbital), and the 2p sublevel which contains three orbitals. So let’s start at the bottom. The 1st energy level is comprised of just one sublevel: 1st 1s It is called the 1s sublevel, and it contains just one orbital. That’s it! +

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**+ 7i 7h 7g 6h 7f 6g 5g 7d 6f 7p 7th 6d 5f 6th 7s 6p 5d 4f 5th 6s 5p 4d**

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…) 7f 6g 5g 7d 6f 7p So let’s look at them again, but let’s spread them out a bit horizontally, so they are not so crowded. 7th 6d 5f 6th 7s 6p 5d 4f 5th 6s 5p 4d 4th 5s 4p 3d 4s 3rd 3p 3s 2p 2nd 2s 1st 1s +

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**+ This is the order in which they were just introduced to you…**

9p 8d 7f 6g 9s 8p 7d 6f 8s 5g 7p 6d 5f 7s 6p 5d 4f 6s 5p 4d 5s This is the order in which they were just introduced to you… 4p 3d 4s 3p 3s There are plenty more, but they go off the screen, so we’re not going to worry about them! 2p 2s 1s +

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**+ 10s 9p 8d 7f 6g 9s 8p 7d 6f 8s 5g 7p 6d 5f 7s 6p 5d 4f 6s 5p 4d 10s**

10h 5s 9s 9p 9d 9f 9g 9h 4p 3d 8s 8p 8d 8f 8g 8h 4s 7s 7p 7d 7f 7g 7h 3p But check out this simple table at right. If you draw diagonal arrows starting at the bottom like this… 6s 6p 6d 6f 6g 6h 3s 5s 5p 5d 5f 5g 4s 4p 4d 4f 2p It shows the precise order in which the energy levels are arranged from lowest to highest! 3s 3p 3d 2s 2s 2p 1s 1s +

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**+ 10s 9p 8d 7f 6g 9s 8p 7d 6f 8s 5g 7p 6d 5f 7s 6p 5d 4f 6s 5p 4d 10s**

10h 5s 9s 9p 9d 9f 9g 9h 4p 3d 8s 8p 8d 8f 8g 8h 4s 7s 7p 7d 7f 7g 7h 3p Watch … 6s 6p 6d 6f 6g 6h 3s 5s 5p 5d 5f 5g 4s 4p 4d 4f 2p 3s 3p 3d 2s 2s 2p 1s 1s +

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**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. s 1 2 p 1 2 3 4 5 6 7 He H d 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:” And let’s also number the groups within each block (1,2,3,4…) f Now let’s take the first ten sublevels (1s, s, 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…

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s f 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? 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s H f 1s1 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? 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s He f 1s2 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 +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Li f 1s2 2s1 Now that the 1s is filled, the next electron goes in the next sublevel – the 2s. Again note how Li is in 2s1. 1s + Its full el. conf. is 1s2 2s1. What is Be’s el. conf?

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Be f 1s2 2s2 Is this what you were thinking? Good. Now look at the periodic table above, what comes after the 2s sublevel? 1s + The 2p sublevel. So what will the next el. conf. be?

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s B f 1s2 2s2 2p1 Is this what you were thinking? Notice how B is in the 2p1 spot. 1s + So its full el. conf. is 1s2 2s2 2p1. What’s next?

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s C f 1s2 2s2 2p2 Is this what you were thinking? Notice how C is in the 2p2 spot. So its el. conf. is 1s2 2s2 2p2 1s + Notice also how when we fill a sublevel…

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s N f 1s2 2s2 2p3 …we put one electron in each orbital until the sublevel is half filled… 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s O f 1s2 2s2 2p4 … and then we go back and start pairing off 1s This is called “Hund’s Rule, but it also referred to as the bus seat rule. Can you figure out why? +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s F f 1s2 2s2 2p5 Look at F. It’s just one electron away from having filled 2p sublevel… 1s + And it’s just one square away from the end of the 2p block.

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**Ne 1s2 2s2 2p6 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5 2p 6 7 2s f 1s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ne f 1s2 2s2 2p6 And then Ne has a completely filled outer level. Na is next. Can you guess where the next electron is going to go? 1s +

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**Na 1s2 2s2 2p6 3s1 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5 2p 6 7 2s f**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Na f 1s2 2s2 2p6 3s1 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 +

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**Mg 1s2 2s2 2p6 3s2 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5 2p 6 7 2s f**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Mg f 1s2 2s2 2p6 3s2 Did you get this one right? 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Al f 1s2 2s2 2p6 3s2 3p1 How about Al’s? See how Al is in the 3p1 spot on the per table 1s + and its el config ends with 3p1

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Si f 1s2 2s2 2p6 3s2 3p2 Now just advance through the next 23 slides, but as you do, make sure you are understanding 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s P f 1s2 2s2 2p6 3s2 3p3 Exactly what is going on… how the el configs simply follow the sequence of the periodic table. 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s S f 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! 1s2 2s2 2p6 3s2 3p4 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Cl f 1s2 2s2 2p6 3s2 3p5 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ar f 1s2 2s2 2p6 3s2 3p6 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s K f 1s2 2s2 2p6 3s2 3p6 4s1 1s +

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**Ca 1s2 2s2 2p6 3s2 3p6 4s2 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5 2p 6**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ca f 1s2 2s2 2p6 3s2 3p6 4s2 1s +

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**Sc 1s2 2s2 2p6 3s2 3p6 4s2 3d1 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Sc f 1s2 2s2 2p6 3s2 3p6 4s2 3d1 1s +

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**Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ti f 1s2 2s2 2p6 3s2 3p6 4s2 3d2 1s +

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4d 5s 4p 3d 4s s 1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s V f 1s2 2s2 2p6 3s2 3p6 4s2 3d3 1s +

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**Cr 1s2 2s2 2p6 3s2 3p6 4s2 3d4 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Cr f 1s2 2s2 2p6 3s2 3p6 4s2 3d4 1s +

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**Mn 1s2 2s2 2p6 3s2 3p6 4s2 3d5 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Mn f 1s2 2s2 2p6 3s2 3p6 4s2 3d5 1s +

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**Fe 1s2 2s2 2p6 3s2 3p6 4s2 3d6 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Fe f 1s2 2s2 2p6 3s2 3p6 4s2 3d6 1s +

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**Co 1s2 2s2 2p6 3s2 3p6 4s2 3d7 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Co f 1s2 2s2 2p6 3s2 3p6 4s2 3d7 1s +

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**Ni 1s2 2s2 2p6 3s2 3p6 4s2 3d8 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ni f 1s2 2s2 2p6 3s2 3p6 4s2 3d8 1s +

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**Cu 1s2 2s2 2p6 3s2 3p6 4s2 3d9 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Cu f 1s2 2s2 2p6 3s2 3p6 4s2 3d9 1s +

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**Zn 1s2 2s2 2p6 3s2 3p6 4s2 3d10 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s 4 5**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Zn f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 1s +

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**Ga 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ga f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1 1s +

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**Ge 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Ge f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2 1s +

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**As 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s As f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 1s +

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**Se 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Se f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4 1s +

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**Br 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Br f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 1s +

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**Kr 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 + 4d 5s 4p 3d 4s s p 1 3p 2 d 3 3s**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Kr f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 1s +

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**Rb 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 + 4d 5s 4p 3d 4s s p 1 3p 2 d**

1 2 p 1 3p 2 d 3 3s 4 5 2p 6 7 2s Rb f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 1s +

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**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. 1 1s2 2 2s2 2p6 3 3s2 3p6 4 4s2 3d10 4p6 5 5s2 4d10 5p6 6 6s2 5d10 6p6 7 7s2 6d10 4f14 5f14

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**The short cut would be: [Ne]3s2 3p5**

For example, Cl (#17) which is right here on the table: So the answer would be 1s2 2s2 2p6 3s2 3p5 The short cut would be: [Ne]3s2 3p5 1 1s2 2 2s2 2p6 3 3s2 3p5 4 5 6 7

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**1s2 2s2 2p6 3s2 3p6 4s2 3d8 Short cut: [Ar] 4s2 3d8 1 2 3 4 5 6 7**

Or how about Ni (#28) 1s2 2s2 2p6 3s2 3p6 4s2 3d8 Short cut: [Ar] 4s2 3d8 1 1s2 2 2s2 2p6 3 3s2 3p6 4 4s2 3d8 5 6 7 4f14 5f14

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Let’s try Bi (#83) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p3 (don’t forget the 4f14!) Short cut: [Xe]6s2 4f14 5d10 6p3 1 1s2 2 2s2 2p6 3 3s2 3p6 4 4s2 3d10 4p6 5 5s2 4d10 5p6 6 6s2 5d10 6p3 7 4f14

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**By the way, the orbitals are not really little empty boxes on a line:**

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 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:

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**Now try some of the problems from the Electron Configuartion worksheet.**

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Electronic Configuration

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