The electron configuration of an element is the distribution of its electrons within atomic orbitals.
Concept: Understanding Periodic Law2m
In this new video, we're going to see what happens when we look at the arrangements of electrons in a given element.
We're first going to say in this chapter, we're going to focus on how an element's electron configuration, which is the distribution of electrons within the shells of an element, relate to its chemical and physical properties. Basically, the way that the elements arrange themselves within the first shell up to the seventh shell will determine how reactive or unreactive an element can be.
We're going to say, quick history lesson, we're going to say in 1870, it was Mendeleev who first organized the 65 elements that were known at that time into what we know as the periodic table. He summarized the way they behave as the periodic law.
Basically, the arranged them in terms of increasing mass. As you notice on the periodic table, the atomic number increases as we gain more protons to make new elements. As a result, the mass also increases. The way the periodic table is set up is basically based on trends that all of them were able to see.
This was ingenious because by doing this Mendeleev was actually able to predict elements before they were even discovered. He realized we went from one element and we skipped several spaces before we found another element. He knew that there must have been elements that we hadn't found yet that fit in those blank spaces. That's why the periodic table at that time and even today is a great and amazing feat that they were able to do way back in the past.
The arrangement of elements within the periodic table is based on increasing atomic mass.
Concept: The Auf Bau Principle3m
Now what we're going to say here is when talking about the electron configuration of an element, we're going to say according to the Aufbau principle, you first have to totally fill in the total, fill in the lowest energy level before moving to the next.
What do I mean by lowest energy level? What I mean by that is we have to completely fill in an electron orbital before we can move on to the next. Basically, here we have 1s, 2s and 2p. Each of those represent different types of electron orbitals.
Basically, the Aufbau principle says that if I'm going to go to 2s, I first have to fill up my 1s completely. We would fill this in with electrons. Remember, s can hold how many electrons? It can hold two electrons. We would have one electron spinning up. To counter-balance that we have a second electron spinning down, so half-arrow pointing down.
We'll learn later that this is a necessary thing because if we have them spinning in the same direction, they would have the same quantum numbers. No two electrons can have the same exact quantum numbers. Remember, within a given electron orbital, we have two electrons max that you can hold. One has to spin up, one has to spin down. That 1s would be completely filled.
We would then move over to the 2s. 2s, s can only hold 2, so it would be one up, one down. Then before we go on to 2p, the 2s would have to be filled in.
This is the Aufbau principle, you fill in the lower energy orbital numbers before you move onto the higher ones. We know that 1s has less energy than 2s. They're both s orbitals, so they have similar energies, but 2s is in the second shell. Because it's in a higher numbered shell, it has more energy. That's the way you have to understand it. They're both s, but they're different because one is in the first shell, one is in the second shell. Being in the second shell would give the 2s ones more energy.
According to the Auf Bau Principle, electrons fill in lower energy orbitals before moving to higher energy orbitals.
Concept: The s,p, d, f sublevels and the Periodic Table4m
Now, for 2p, we'll see what happens when we have to fill in 2p when we go lower down. But before we do that, we've been talking about the electron configuration. How am I supposed to know what the electron configuration of an element is? The way we're able to do this is basically in two ways, depending on what your professor feels like teaching you.
One way, we're going to look at the periodic table in a very different light. We're accustomed to seeing the periodic table with its elements and its atomic numbers and its atomic masses. In this image, we basically break down the periodic table in this way. We're going to look at it in this fashion in order to write the electron configuration of the element.
Just realize that the periodic table is separated into different sections. We're going to say Group 1A and 2A are what we call the s-block. Helium, which is over here, would be part of that. It would be grouped in together with it. Remember, how many electrons can the s hold? S can hold two electrons. If we're talking about the s-block, we're talking about two groups, Group 1 and Group 2. Each group has a total of one electron it can hold.
Down here in the pit, we call this our d-block. Remember, how many electrons can the d-orbital hold? It can hold up to 10. Look, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.
Here, 3A to 8A, excluding helium, they're called the p-block. These are our p-block elements. How many electrons can the p hold? P orbital can hold up to 6 electrons, 1, 2, 3, 4, 5, 6.
Then, finally, down here with the lanthanides and the actinides, these are our f-block. F can hold up to 14. So, if you count this you'll get 14 total.
The periodic table is basically arranged in a way where this makes sense.
Also, what you should realize here is that the periods, remember, this is period 1, period 2, all the way to period 7, the period number reflects the shell number. We have 7 periods as of now, so we have 7 shells as of now for our biggest elements. We're going to say here that the period number basically tells me the number of the orbital. In period 2, we have 2s and 2p. In period 3, we have 3s. We also have 3d and we have 3p. For period 4, we have 4s, 4d, 4p, and 4f. If you add those up, that tells you the total number of electrons within shell 3, shell 4. What you should also realize here from this trend is when we go from 4s, we drop down one when we go to the d-block, so it would drop down to 3d.
Concept: The Electron Configuration of Fluorine4m
Now let's see how this would work if we were asked to find the electron configuration of an element. You'll see how easy it is when you use the periodic table in this way. I would recommend when doing all of the electron configuration type questions, pull this periodic table out and use it to figure out what the electron configuration is of any type of element of ion.
Here I told us to find the electron configuration of fluorine. I want to take myself out of the image, guys, so we have more room to work with.
We're looking for the electron configuration of fluorine. I tell you that fluorine has 9 electrons. Let's look on the periodic table and see where do we find fluorine. Fluorine would be right here. To find it's electron configuration, we're basically going to count to it. We're going to say fluorine starts off as 1s because we have to pass 1s to get to f, right? 1s and there's 1, 2 in the 1s. Now we're at 2s, 1, 2, so 2s2. Now, f is found in the 2p section. We have to land directly on top of it, sp 2p, 1, 2, 3, 4, 5. That lands us right there. That would be the electron configuration of fluorine by using this version of the periodic table.
There's another type of way we could have solved for the electron configuration of fluorine. It's an older way, but it still works too. It's called using the Aufbau diagram, which is this little image right here.
We're going to say here the way the Aufbau diagram works is like this. We're going to fill this out in this way. And you'll see how we count this. This way is similar to the way we're using the periodic table. Personally, I think it's more of a nuisance to use it because you first have to write it and you have to do all these arrows in order to follow the path. My opinion, it's better to use the periodic table version.
Let's use this Aufbau diagram to find the electron configuration of fluorine. We'd start off with 1s and how many does s hold? It holds 2, so 1s2. That gets us here. Then we loop around to this one, 2s2. Then we loop around 2p, and we have to make sure we land directly on fluorine. It would be 2p5. Basically go 3s2. If you were continuing. Loop around, 3p6, 4s2. Loop around again.
This is an older way to do the electron configuration of elements. I personally think that the periodic table way is much better. But if you're more accustomed to the Aufbau diagram, that's up to you.
By using the Periodic Table, you can determine the electron configuration of fluorine.
Concept: Hund's Rule3m
Now, we've done the electron configuration. Now, you see these little boxes here, these represent the electron orbitals for each one of those sublevels that we have here. We're going to fill them in. We call these electron-box diagrams, where we physically show the electrons within each one of these orbitals.
We're going to say we start out with one s. How many does s hold? It holds two. Remember, I told you, they have to spin in opposite directions. One spins up, the other one spins down. That's 1s2. We can then move on to 2s following Aufbau principle because we have to fill in the lower orbital first before we move onto the next one. This one also has two. One up, one down.
Now, in 2p we have five electrons. But here's the thing, all three of these electron orbitals, all three of them are p, 2p orbitals, so they all have the same exact energy. We're going to have to follow Hund's Rule to correctly fill it out. Hund's Rule states that electron orbitals that are degenerate, so remember that word, degenerate, are first half filled before they are totally filled. Degenerate just means that they have the same amount of energy. We know that these three electron orbitals have the same energy because they're all two orbitals and they're all p orbitals, so they're all 2p orbitals.
We're going to half fill them first. We'd say up, up, up. You half fill them first. You do this because they all have the same energy. Then you loop back around. Down, down. That's how you would fill out the 2p. Just remember that. When you're dealing with degenerate orbitals, they have the same number, they have the same letter, therefore they have the same energy. You half fill them first before you totally fill them in. Come back around and start filling them pointing down.
1S and 2s are not degenerate. They may have the same letter, but they definitely don't have the same number. 1 is 1 and 2 is 2. Because they have different numbers, they have different energies.
That's the beginning of electron configuration, guys. There are different types of electron configurations that we're still going to need to know and master, but this is the beginnings of it. Remember, as long as you can follow either the periodic table version or the Aufbau diagram version, then you should be able to do the electron configuration of many different types of elements. Just remember, what does this periodic table version look like and use it to answer those types of questions.
In a condensed electron configuration we shorten our amount of writing by including a noble gas.
Example: Write the condensed configuration for each of the following elements:
Co (27 electrons)
Se (34 electrons)5m
Problem: Write the condensed configuration for each of the following elements: Ag (47 electrons)2m
Concept: Inner Core vs. Valence Electrons3m
We're going to learn the difference between inner core electrons and what are called valence electrons.
What we're going to say here are valence electrons are basically the electrons we found in the outer most shell. The outer most shells are usually the electron orbitals with the biggest number. Valence electrons are going to become more important when we move over to bonding and we have to draw chemical structures. We have to realize there that all of the bonds that we use to form chemical bonds are using valence electrons.
We're going to say that main group metals, whatever your main group metal number is, that's also the number of valence electrons that element has. What do I mean by this? For example, lithium, lithium is in group 1A, so lithium has one valence electron.
We're going to say for main group metals, we're going to say valence electrons, so the number of valence electrons equals group number. These guys would have one valence, these guys would have two valence, three valence, four valence, five, six, seven and eight valence electrons. Except for helium. Helium would have two valence electrons.
That's just for main metals. Now, we know that the periodic table is not made up of only main metals. The periodic table is also made up of transition metals. When it comes to transition metals, they kind of mess up everything. For that part most professors seldom ask for the number of valence electrons of a transition metal.
But if they were to ask you the electron configuration or valence electrons of a transition metal, you just have to remember, for the most part we can figure out the number of valence electrons of these transition metals here. The lanthanides and the actinides down here, because they have f electrons, f orbital electrons, we'd have to use quantum theory in order to solve the number of valence electrons. This is just chem one, so you don't have to do quantum theory.
If they're going to ask you a number of valance electrons for transition metals, it would be these transition metals in here. We'd simply say that their number of valence electrons, so for transition metals, these transition metals, we're going to say number of valence electrons equals number of electrons in the s and d orbitals. By s I mean the highest numbered s. The largest s orbital numbered and also the d orbital. Take those two, add them together and that will give us our total number of valence electrons.
Example: How many core (inner) and valence electrons are present in each of the following elements?
P Al Mn5m
Give the ground-state electron configuration for silicon (Si).
Express the complete electron configuration using superscripts where appropriate. For example,the configuration for Li would be entered as 1s22s1.
Give the actual ground-stateelectron configuration for copper (Cu).
Express the electron configuration using superscripts where appropriate. For example, the configuration for Li would be entered as 1s22s1.
Which of the following represents an excited state of an atom?
What is the electron configuration of Fe3+?
Which of the following electron configurations is correct for molybdenum, 42Mo, in its ground state?
What is the valence-shell electron configuration for the shaded group in the periodic table given below?
The electron configuration of Gd is [Xe]4f75d16s2. How many unpaired electrons are in this atom?
Which atom below contains the greatest number of valence electrons?
E. All of the above contain the same number of valence electrons
Which of the following electron configurations is correct for antimony ( 51Sb)?
The only noble gas that does not have the ns 2 np6 valence electron configuration is____________________.
E) All noble gasses have the ns 2np6 valence shell electron configuration
Give the full ground-state electron configuration for the element. S
e. none of these
When forming cations, electrons are removed first from orbitals that are bigger rather than necessarily those with higher energy. Given this, what is the electron configuration of the cobaltic cation, Co3+?
(A) [Ar] 4s2 3d7
(B) [Ar] 4s2 3d4
(C) [Ar] 3d5
(D) [Ar] 4s2 3d10
(E) [Ar] 3d6
The electron configuration for the Os 3+ ion is:
A) [Xe] 4f13 5d6
B) [Xe] 5s2 4f11 5d6
C) [Xe] 5s2 4f14 5d6
D) [Xe] 4f14 5d5
E) [Xe] 5s2 4f14 5d3
An element E has the electronic outer shell configuration ns2 np4. What is the formula of its compound with lithium?
Which electron configuration is incorrect?
a. Zn: [Ar]3d 10 4s 2
b. Ca: [Ar]4s 2
c. Cr: [Ar]3d 4 4s 2
d. Ag: [Kr]4d 10 5s 1
e. All the above are correct.
What is the electron configuration for the Ni 2+ ion?
a. [Ar]3d 8 4s 2
b. [Ar]3d 10 4s 2
c. [Ar]3d 7 4s 1
d. [Ar]3d 8
e. [Ar]3d 6 4s 2
Which of the following atoms is listed with an INCORRECT electron configuration?
A. Br - [Ar]4s2 3d10 4p5
B. Pb - [Xe]6s2 5d10 4f14 6p2
C. Mo - [Kr]5s2 4d4
D. Y – [Kr]5s2 4d1
E. Fe - [Ar]4s2 3d6
Which of the following is the correct electron configuration for the ferric cation?
A. [Ar]4s2 3d3
B. [Ar]4s2 3d4
C. [Ar]4s2 3d6
Write the electron configurations for the following ions or elements:
example: Mg [Ne](3s)2
Fill in the blanks with the correct ground state electron configuration (noble gas configuration) for the given atom or the atom for the given ground state electron configuration.
Which of the following individual atoms has a paramagnetic electronic structure?
What is the expected ground state electron configuration for Zr 2+ ?
1. [Xe] 6s25d4
2. [Kr] 5s24d2
3. [Kr] 5s24d4
4. [Xe] 6s 2
5. [Kr] 5s 2
6. [Kr] 4d 2
8. [Xe] 5d 2
10. [Kr] 5s14d5
Give the electron configuration for the Ti 2+ ion.
When dealing with electron configurations it's best to visualize the Periodic Table in this format.
The electronic configuration of Zn2+ is
A. [Ar] 4s2 3d10
B. [Ar] 4s0 3d10
C. [Ar] 4s2 3d8
D. [Ar] 4s2 4d8
E. [Ar] 4s0 4d10
What is the electronic configuration of Ga 3+ ion? ( Ga has an atomic number of 31 )
a. [Ar] 4s1 3d9
b. [Ar] 3d10
c. [Ar] 4s2 3d8
d. [Ar] 4s1 4d9
e. [Ar] 4s2 4d8
Which of the following statements is/are true?
i. the electron configuration of copper, Cu, is [Ar]4s 23d9
ii. the electron configuration of iron(II), Fe2+, is [Ar]3d 6
iii. the electron configuration of molybdenum, Mo, is [Kr]5s14d5
a. i only
b. ii only
c. iii only
d. i and ii
e. ii and iii
Write the ground-state electron configuration of a lead atom.
1. [Xe] 4f 145d106s16p3
2. [Xe] 4f 145d106s26p2
3. [Xe] 4f 145d 56s16p67s2
4. [Xe] 4f 145d106p4
5. [Xe] 4f 145d 96s26p3
How many p electrons does Se (atomic number 34) possess?
Which of the following species is isoelectronic with S 2–?
2. Br –
4. As 3–
5. Mg 2+
Choose the ground state electron configuration for Fe 2+.
One of the following does NOT represent the ground state electron configuration for an atom. Which one?
1. [Ne] 3s2
2. [Ne] 3s2 3p6
3. [Ne] 3s1
4. [Ne] 3s2 3p5
5. [Ne] 3s1 3p3
What is the electronic configuration of tellurium (Te)?
1. 1s2 2s2 2p6 3s2 3p6 4s2 4p6 5s2 4d10 5p8 6s2 5d6
2. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4f14 5p2
3. 1s2 2s2 2p6 3s2 3p6 4s2 4p6 5s2 6s2 6p6 4d10 7s2
4. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4
5. 1s2 2s2 2p6 3s2 3p6 3d10 3f14 4s2 4p6 4d4
The electron configuration of a vanadium atom (V) is
a) [Ar] 4s24p3
b) [Ar] 4s23p3
c) [Ar] 4d34s2
d) [Ar] 3d5
e) [Ar] 3d34s2
A student wrote that an element had the electron configuration 1s22s22p63s23p64s23d10. If the element forms an ion, what is its most likely charge?
e) 0, it is a noble gas
How many valence electrons does an antimony (Sb) atom have?
In what group of the periodic table is the element with the following electron configuration?
Which of the following is the correct electron configuration for nitride ion?
All of the following electronic configurations are correct except
a) 20Ca [Ar]4s2
b) 25Mn [Ar] 3d54s2
c) 29Cu [Ar] 3d104s1
d) 50Sn [Kr]4d105s25p2
e) 86Rn [Xe]5d106s26p6
How many electrons does a stable gallium, 31Ga3+, ion have?
All of the following species are isoelectronic except
d) F -
Which one of the following species is not isoelectronic with Kr?
How many core electrons does an atom of bromine have?
All of the following ions have the electronic configuration of a noble gas except
b) H -
d) Cl -
Which ground-state electron configuration is incorrect?
a) Cr: [Ar]3d6
b) Ca: [Ar] 4s2
c) Na: 1s2 2s2 2p6 3s1
d) Zn: [Ar] 3d10 4s2
e) Kr: [Ar] 3d10 4s2 4p6
From a consideration of electronic configurations, which of the elements indicated below would be classified as a transition element?
a) 1s2, 2s2, 2p2
b) 1s1, 2s2, 2p6, 3s1, 3p5
c) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2
d) 1s2, 2s2, 2p6, 3s2, 3p6,3d5, 4s2
e) 1s2, 2s2, 2p6, 3s2, 3p6,3d10, 4s2, 4p6
What is the electron configuration of Ni 2+?
a) [Ar] 3d6 4s2
b) [Ar] 3d7 4s1
c) [Ar] 3d8
d) [Ar] 3d8 4s2
e) [Ar] 3d8 4s1
The electronic configuration of the Al 3+ ion is
Which of the following species is isoelectronic with Kr?
What is the electronic configuration of a stable sulfide ion?
The species O 2-, F -, N 3- and Na+ are all
Which of the following sets contains species that are isoelectronic?
A) Cl, Ar, K
B) F -, Ne, Na +
C) F, Ne, Na
D) Al 3+, S 2-, Ar
E) P 3-, S 2-, Ar -
Write the electronic configuration for the following elements and ions:
How many inner shell (core) electrons do the following elements have, respectively?
Hydrogen, Helium, Lithium and Berylium
(A) 1, 1, 1, 1
(B) 0, 0, 1, 1
(C) 0, 0, 2, 1
(D) 0, 0, 2, 2
(E) 2, 2, 2, 2
Choose the ground state electron configuration for Mn 4+.
The atomic numbers (Z), electron configurations, and numbers of unpaired electrons for five ions are listed in the following table. Assume that all unpaired electrons have parallel spins. Indicate the element symbol, charge, and energy state (ground or excited) for each of the five cases.
Molybdenum (Mo) is an element in which the spin pairing energy is > than the promotion energy. With that in mind write the electron configuration for the neutral atom and the +1 ion.
Write the electron configurations for the following elements and ions.
If the ground state electron configuration of an element is [Ar]3d 104s24p3, what is the typical charge on the monatomic ion of the element ?
Which element has the fewest number of valence electrons?
Magnesium and sulfur react to form MgS, an ionic compound. The magnesium ion,Mg2+, has ______ electrons in its highest occupied energy level.
The C+ cation has how many total electrons and how many valence electrons?
1. 6; 5
2. 6; 6
3. 7; 6
4. 5; 4
5. 5; 3
6. 6; 4
7. 6; 3
8. 7; 5
9. 7, 8
Write the ground-state electron configuration of a lead atom.
1. [Xe] 4ƒ145d106s16p3
2. [Xe] 4ƒ145d106s26p2
3. [Xe] 4ƒ145d56s16p67s2
4. [Xe] 4ƒ145d106p4
5. [Xe] 4ƒ145d96s26p3
How many p electrons does Se (atomic number 34) possess?
Which of the following species is isoelectronic with S2- ?
2. Br –
Which element has an outer electron configuration of ns 2np4?
The electron configuration of Cr 3+ is
How many core and valence electrons does an atom of bromine possess?
A. 18 core, 17 valence
B. 28 core, 7 valence
C. 30 core, 5 valence
D. 20 core, 15 valence
E. 10 core, 25 valence
Choose the electron configuration for Cr 3+ .
Which principle indicated that electron placement begins with the lowest energy level?
B. Pauli Exclusion
Which two elements have the same ground-state electron configuration?
A. Cl and Ar
B. Cu and Ag
C. Pd and Pt
D. Fe and Cu
E. No two elements have the same ground-state electron configuration.
The electron configuration for Ge is __________.
A. 1s 22s 22p 63s 23p 64s 24d 104p 2
B. [Ar]4s 23d 12
C. 1s 22s 22p 63s 23p 63d 104s 24d 2
D. 1s 22s 23s 23p 63d 104s 24p 2
E. 1s 22s 22p 63s 23p 64s 23d 104p 2
Which of the following is a reasonable electronic configuration for neutral Tin (Sn)?
Which is a possible electronic configuration for neutral silicon?