The Electron Configuration - Video Tutorials & Practice Problems
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The electron configuration of an element is the distribution of its electrons within atomic orbitals.
The Electron Configuration
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concept
The Electron Configuration
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Now before we can talk about electron configurations, realize first that Mendeleev organized the elements in the periodic table through periodic law. And periodic law says that when arranged by increasing atomic weight, elements in the same group share similar chemical properties. These properties would influence their electron arrangements, and by extension their configurations, it would affect their trends in reactivity, and their atomic structures. So remember, in order to first understand electronic configurations, we need to go into periodic law first, and it helps us to understand
Periodic Law: elements in same group arranged by increasing atomic weight, share chemical properties, which influence electron arrangements, trends and atomic structure.
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concept
The Electron Configuration
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As we stated earlier, the periodic law influences the electron arrangements of the elements, and the electron orbital diagrams are the visual representation of within orbitals. Now we're going to say here we have what are called degenerate orbitals. These are electrons in the same set of orbitals having same energy, and they're filled using Hund's rule. Now Hund's rule says that these degenerate orbitals are first half filled before being totally filled. So if we take a look here, we have our s sublevel or s subshell. S can hold a maximum of 2 electrons. It has 1 orbital. Within that orbital we have 2 electrons, one spins up, one spins down. So that would mean that the s sublevel has a maximum of 2 electrons. For p sublevel, we have 3 orbitals. Following Hund's rule we would half fill them first. So we go up, up, up, each orbital we know can hold a maximum of 2 electrons so we come back around, down, down, down. So the p sub level holds a maximum of 6 electrons. For d, we have 5 orbitals here. Hund's rule says we half fill them first, since they're all d set of orbitals, they all have similar energy. So then we come back around, down, down down down down for a total of 10 electrons. And finally the f sublevel has 7 of these orbitals, half fill them again according to Hund's rule. So when we half fill them according to Hund's rule, come back around to totally fill them in. When we do that we get a total of 14 electrons. So just remember periodic law influences the electron arrangement of elements, and it's these orbital diagrams that depict the visual representation of electron within any given orbital, based on subshell level or subshell, letter. So just keep that in mind, s can hold a maximum of 2 electrons, p can hold up to 6, d can hold up to 10, and f can hold up to 14.
According to Hund's Rule, degenerate orbitals are first half filled before being totally filled.
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example
The Electron Configuration Example 1
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Here it says we need to properly fill in the orbitals of an atom that possesses 8 electrons within its d set of orbitals. Now we know that these are d set of orbitals because there's 5 of them. We have to fill in 8 electrons. Remember, since they're all the same set of orbital types being d, they all have the same energy and therefore are degenerate. We would half fill them based on Hund's rule. So we go up, up, up, up, up for our first 5. We need to fill in 8, so come back around. Down, down, down. So we stop there because again we only have 8 electrons to fill in, so here we don't need to completely fill in the last 2. They'll be left just 1 electron in each. So this would be the way to properly fill in these d set of orbitals that have 8 total electrons.
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Problem
Problem
Which electron configuration represents a violation of Hund's Rule?
A
B
C
D
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concept
The Electron Configuration
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When writing the electron configuration of an element, it's important that it represents the distribution of electrons from 1 s to 2 s to 2 p and so on within orbitals using the Aufbau principle. Now with the Aufbau principle it says, starting with 1 s, we're going to have electrons filling lower energy orbitals before moving on to higher energy orbitals. We begin with 1 s when we're doing the the full ground state electron configuration of an element or an ion. To help us with this, you could take the Aufbau diagram approach. We start out with 1 s, then we move on, loop back around to 2 s, then we loop back around to 2p, then to 3s, then we loop back around to 3p, and then 4s, then continuously loop back around to 3d, to 4p, to 5 s. Now, this is our off ball diagram. In the off ball diagram we have here one s all the way down to 8 s. Then we have 2p to 3 to 7p. Then we have 3d to 6 d, and then we have 4 f and 5 f. Another way we can look at determining the electron configuration has to do more with the periodic table. So if you click on the next video, let's reimagine what the periodic table will look like when dealing with the electron configuration of elements and ion.
According to Auf Bau Principle, starting from 1s, electrons fill lower energy orbitals before filling higher energy orbitals.
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concept
The Electron Configuration
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So here if we reimagine the periodic table, we'll see it in this depiction. Now realize here we have blue, we have yellow, we have purple, and we have red sectors. Now, each of these is called a block s. The s block is what's in blue, this is the p block, the d block, and the f block. Remember the s sublevel has 1 orbital and that one orbital can hold a maximum of 2 electrons, which is why the s block is these 2 columns, to represent the 2 maximum electrons that the s sublevel can hold. The p sublevel has 3 orbitals, right, and each one again can hold a maximum of 2 electrons. So p theoretically can hold a maximum of 6 electrons. That's why the p block has 1, 2, 3, 4, 5, and 6 slots for it. D can have up to 10 electrons because it has 5 orbitals, and if you count you'll see in here there's 10 spots. And then for the f sub levels, they can hold up to 14 electrons, and if you were to count these rows in red you'd see they come out to 14. Now, realize here that in this periodic table the first slot here, which represents hydrogen, starts off our electron configuration as 1 s 1. Then as we move to the next one we add another electron, electron, so helium is 1 s 2. Then when we get to the 2nd row, since we're in the 2nd row, we now have 2. This is still the s block, so this is 1 s 2, 2 s 1, and it continues onward and onward. Over here we'd go 1 s 2, 2 s 2, 2 p 1. So following this pattern this would be 3 s, 4 s, 5 s, 6 s, and 7s. And then here this would be 3p4p, 5p, 6p, and 7p. When we go to the d block, realize that it's gonna drop down by 1. So here this is 4 s, but then when we go to d block, it drops down by one number, so now it's 3 d. This would be 4 d, 5 d, and 6 d. Now, notice how this number goes from 57 to 72, that's because 58 to 71 are here. Remember this this red line here says that this entire red row exists in between 57 and 72. And then we go between 89 and 104 because 90 to 103 is down here. These are your f blocks. They also drop down by one number. So this is 4 f and 5 f. So basically, if you can reimagine the periodic table in this fashion, you can use it to figure out the electron configuration of any element or ion given to you. So we're gonna put this periodic table to use in order to do future electron configurations.
Electron configuration of Boron (Z= 5) is 1s2 2s2 2p1.
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example
The Electron Configuration Example 2
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1m
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To help us with this example question, I decided to leave this periodic table up so we can see how to best use it. Here it says write the ground state electron configuration for the following element. Here we're dealing with fluorine, and they tell us that it has an atomic number of 9, which means it has 9 electrons. On this periodic table, we find fluorine right here. Ground state means that we're gonna start out with 1 s orbital and work our way up to fluorine. So we're gonna count to fluorine. So we'd say 1 s 2, 1 s 2, 2 s 2 because of 1, 2 slots. And then we have to count to f, so that would be 2 p, we're in the 2 p row. And how many slots do we have to count to to get to fluorine? 1, 2, 3, 4, 5. 2p5. So here, this would be the ground state electron configuration of the Fluorine atom. And realize here that these are the number of electrons. So when you add them up, 2+2+5, that gives me 9 electrons, which is related to the atomic number here of Fluorine. Remember, when an element is neutral, its atomic number tells us both the number of protons and the number of electrons. So again, rely on this depiction of the periodic table to help guide you to the right electron configuration of any element or ion given to you.
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Problem
Problem
Which electron configuration represents a violation of the Auf Bau Principle?
A
B
C
D
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Problem
Problem
Identify the element with the given electron orbital diagram.
A
Silicon
B
Fluorine
C
Sulfur
D
Chlorine
E
Phosphorus
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Problem
Problem
Write the electron configuration and electron orbital diagram for the following element:
Mn (Z = 25)
A
1s2 2s2 2p6 3s2 3p6 4s2 3d5
B
1s2 2s2 2p6 3s2 3p6 4s2 4d5
C
1s2 2s2 2p6 3s2 3p6 4s2 3d4
D
1s2 2s2 2p6 3s2 3p6 4s2 3d5
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Problem
Problem
Write the ground-state electron configuration for the following element: