Hey khan, just a quick message, not sure if you'll see this but I use to watch your videos through school and university, now I am working professional thanks to the classes I passed with your help. Hugely grateful for you help. Your student From Australia
I spent 18 hours straight last quarter listening to (mostly) your lectures. Well, cramming went awesome, and I did alright on the midterm, but due to a lack of lab attendance, I'm back again for your awesome videos. Just wanted to say thank you for being a life saver!
I've never really understood why the d shells were in one energy state behind, but what khan said makes sooo much sense. Hands down best teacher on youtube.
All of this was daunting in the first few minutes of the module, but I quickly caught on. I really like how pedagogic these videos are. I feel Khan's thinking style is very close to mine. Being explicit is good.
THANK YOU!! you're videos really help. i'm in AP chem now... I watch these videos right before a test or when I don't understand a concept taught in class. my teacher in regular chemistry taught us that it's a sin (Sn) to forget tin... :)
thanks mate!!!!! I've been stressing about how on earth to count valence electrons without drawing out the whole frikin chart which would be a waste of time in an exam, but you've shown me an easier way to count them! Thankyou again!
THANK YOU, you literally just taught me everything my teacher failed to teach me in one week, in 15 minutes... and i have an exam tomorrow. khan forever
I really like that he uses reason to describe the orbital clouds. This is the best explanation I have heard short of unification theory. Way better than public schooling :)
That explanation of backfilling around 5:10. Absolutely amazing. What a beautiful image; it's easier to fill 4s than 3d, makes sense, and it's cool to see the density of electrons can get so high, like intricate ethereal puzzle pieces fitting together. It's got me wondering about how close orbitals can get, what with pauli and ∆p∆x ≥ h/4π. What period do the f orbitals start, and how far back do they backfill?
This is amazing, all through this year after having non-science a levels - this has been my saviour for my foundation course and subsequent degree. Thank you for making these videos!
Man, I totally get that the model is just that - a model - but good grief that took a concept that was so abstract and frustrating to me and really helped me understand it. I really appreciate your multi-modal approaches with these videos, thank you!
Okay so I just noticed something that helped me in writing out the electron configurations for elements. 1.When filling out the S shells you will be filling for the first two groups with the exception of He 2.The P shell fills electrons for groups 3-8 3.The D shell fills the electrons that are transition metals I hope this helps and if there is anything else that can be added to this or some of my information is incorrect then comment below on what should be fixed.
we don't say valence electrons in Britain. Instead, when an atom goes beyond 1 shell, we say 2nd shell, 3rd, 4th, 5th and so on. still a useful video, good job
I think you've misunderstood what [Kr] means in this notation. It's basically a placeholder for the full electron configuration of krypton. So [Kr] stands for: 1s² 2s² 2p⁶ 3s¹ 3p⁶ 4s² 3d¹⁰ 4p⁶ That's a lot to write down, so it's shortened to [Kr]. When Sal writes [Kr] 5s² 4d¹⁰ 5p² for tin, that means we have 14 more electrons than are found in Krypton and they're in the 5s, 4d and 5p orbitals.
What you're saying makes sense, but my textbook says that electrons are categorized into 3 groups. The inner electrons, the outer electrons, and the valence electrons. for main group elements the outer electrons are the valence electrions. but for the transition elements, all the (n-1) d elections are the valence electrons, and the outer electrons are those in the highest energy level (the highest n value)
they use 8 because it takes more energy to open up a new shell, when their are 8 the electrons won't jump to other atoms to either get rid of or aid the extra electrons so its more stable and balanced
In the Kaplan mcat book, every outter electron regardless of energy level is a valence electron. So for example Ir would have 2 s valence electrons and 7 d valence electrons for a total of 9
Thank you so much for this, after listening to your lesson on the periodic table I am now understanding this better than having two science teachers explain this configuration.
@clemens2003 The rule is a function of the nuclear size, and the distance of the outer shell to the nucleus. It's simply that 8 electrons in the outer shell is more stable. That's when all forces are in balance. (atomic, magnetic, strong, weak, gravity) For star systems, the distances are so great that only one force is involved, gravity. The orbiting bodies will configure for lowest energy state for gravity. Also the bodies are not uniform, like electrons, protons, and neutrons.
I like Khan Academy but honestly I barely learned anything from this video mainly cuz you keep moving from topic to another topic but nonetheless thanks for educating me!!
Valence eletrons are not only those on the outer shell. "The valence electrons are instead defined as those outside a noble-gas core" (Wikipedia: wikipedia(dot)org/wiki/Valence_electron)
Wait, so Helium has 2 protons and 8 electrons in it's outer shell? Is that correct or am I missing something? I thought an element in equilibrium had the same number of electrons as protons.
Vector Boris Oh ok, that threw me off, is it usually located in the S block on normal charts? I notice it's colored like the ones in the P block, that crap makes it super confusing!
@Giallorossi03 you guys...the periodic table consist of elements that are named in Latin and Greek. Tin is the English notation for this element. But yeah, it is kinda funny =D
Hello:) I'm from Italy..your lessons are really awesome, and your way of teaching isn't as the way of teaching of my chemistry teacher, , thank you so much, i will follow you for all my university career , and please continue to do other lessons of chem, anatomy and biology.. bye bye from Italyyyyyyy :) anyway sorry for my poor English ..and hope to see other lessons on youtube ... !!!!!
perhaps you should look up the recent articles by Eugen Schwarz in the Journal of Chemical education. I assure you what I am saying is correct. Most textbooks have it wrong. 3d actually fills before 4s. That's precisely why 4s is preferentially ionized. I have been teaching general chemistry for 30 years, the past 15 to classes of 350-450 students in US colleges, most recently UCLA. I am not a kid off the street just trying to disrupt this website or trying to undermine the amazing Kahn.
More importantly, the 4s orbitals DO NOT fill before the 3d in transition metal atoms. THis is a common textbook error. The 3d are filled first but the final 2 electrons enter the 4s orbital to minimize repulsion. Please see the blogs on my website on this topic
Dear Prof. Khan, is it possible to write Fe as [Ca]3d6? or would it be better to write it as [Ar]4s23d6 since it shows that 4 is the highest energy shell?
You're really great ! thanks you ! btw - you forgot to mention that helium doesn't infact have 8 electrons (it's written under 8) also wrote that Cu Ag and Au would have 2 electrons in their outer shell although they actually have 1 since they give away 1 to fill their d shell. But thanks alot !
Hi, as to why d fills n-1 rather than n (5:18) may it be a screen effect : Electron already in place screen the nucleus and allow new electron to be closer with the same energy ?
at 9:50, for Sn, if we ionized it, removing 5p2 and 5s2, and then had enough energy to rip yet another electron off, which electron would go first? In other words, given [Kr]4d10 configuration of Sn, which would be the next electron to be lost? From d orbital?
My theory was that D and F electrons had stronger pulling forces towards the nucleus, which somehow leeches kinetic energy and centripetal force from the electron. $0.02
wow , you my friend can be a very successful university teacher , you explain this things like an alien , u seem to be very smart :) , thanks a lot for sharing ur wisdom mate
So if the electron configuration of Cr is [Ar] 4s^1 3d^5 due to Hund's rule. Then Cr has 1 valence electron right? I'm sure someone already asked this question but it doesn't seem very recent... Thank You
@PINKmeUP67 It's 7 because the highest energy level is 4. [Ar]4s2 3d10 4p5 The 4s2 and the 4p5 add to 7. That 3d10 portion is what he was talking about when he mentioned the back filling. Make sense?
12 years to the future. anyway, s, p, d, and f orbitals can hold 2, 6, 10, and 14 electrons respectively. idk why 8 is the "stable" amount of valence electrons but if you take the average of the maximum numbers of electrons those orbitals can hold: 2 + 6 + 10 + 14 = 32 32/4 = 8 maybe it has something to do with that?
He did not make that mistake, he only made one mistake which is saying that Sn is Selenium but Sn is Tin, Se is Selenium. He was referring to the electronic configuration of Tin which is [Kr]5s^2 4d^10 5p^2. Because after you count the entire periodic table before Krypton it ends at the 4p^6 and since Sn(tin) is found on the 5th period or 5th energy level it should start with a 5s and not a 4s.
Sal you said in this video that atoms are best paired up when there are 8 electrons on the outside? Does this in anyway to your knowledge, theory, fundamental ideas have any relation to our solar system only having 8 planets? Has this been researched or have any theories been formed? Just something that crossed my mind today.
Hey khan, just a quick message, not sure if you'll see this but I use to watch your videos through school and university, now I am working professional thanks to the classes I passed with your help. Hugely grateful for you help.
Your student
From Australia
I spent 18 hours straight last quarter listening to (mostly) your lectures. Well, cramming went awesome, and I did alright on the midterm, but due to a lack of lab attendance, I'm back again for your awesome videos. Just wanted to say thank you for being a life saver!
I've never really understood why the d shells were in one energy state behind, but what khan said makes sooo much sense. Hands down best teacher on youtube.
I didn’t try to think
Ohhh, this is why... I didn't even think about it
Thank you SO MUCH for making this video. I had college chemistry and have forgotten it. This was a great review!
All of this was daunting in the first few minutes of the module, but I quickly caught on. I really like how pedagogic these videos are. I feel Khan's thinking style is very close to mine. Being explicit is good.
THANK YOU!! you're videos really help. i'm in AP chem now... I watch these videos right before a test or when I don't understand a concept taught in class.
my teacher in regular chemistry taught us that it's a sin (Sn) to forget tin... :)
thanks mate!!!!! I've been stressing about how on earth to count valence electrons without drawing out the whole frikin chart which would be a waste of time in an exam, but you've shown me an easier way to count them! Thankyou again!
ahhh omg, the feeling i get, when you kinda rhetorically ask a question and i can actually answer it and follow along..ahhhh ily dude. life saver.
And now you are old
THANK YOU, you literally just taught me everything my teacher failed to teach me in one week, in 15 minutes... and i have an exam tomorrow. khan forever
So many years that none of this really made sense, it's finally dropping in thanks to Sal.
You are better than the lecturer in my uni :) keep it up
Shenan De Silva so true
I really like that he uses reason to describe the orbital clouds. This is the best explanation I have heard short of unification theory. Way better than public schooling :)
That explanation of backfilling around 5:10. Absolutely amazing. What a beautiful image; it's easier to fill 4s than 3d, makes sense, and it's cool to see the density of electrons can get so high, like intricate ethereal puzzle pieces fitting together. It's got me wondering about how close orbitals can get, what with pauli and ∆p∆x ≥ h/4π. What period do the f orbitals start, and how far back do they backfill?
This is amazing, all through this year after having non-science a levels - this has been my saviour for my foundation course and subsequent degree. Thank you for making these videos!
Man, I totally get that the model is just that - a model - but good grief that took a concept that was so abstract and frustrating to me and really helped me understand it. I really appreciate your multi-modal approaches with these videos, thank you!
Okay so I just noticed something that helped me in writing out the electron configurations for elements.
1.When filling out the S shells you will be filling for the first two groups with the exception of He
2.The P shell fills electrons for groups 3-8
3.The D shell fills the electrons that are transition metals
I hope this helps and if there is anything else that can be added to this or some of my information is incorrect then comment below on what should be fixed.
Listening to Salman Khan's lectures is like having Ray Romano as a crazy substitute teacher. Best day EVER.
we don't say valence electrons in Britain. Instead, when an atom goes beyond 1 shell, we say 2nd shell, 3rd, 4th, 5th and so on.
still a useful video, good job
Thanks Sal! You're doing an amazing thing!
I think you've misunderstood what [Kr] means in this notation. It's basically a placeholder for the full electron configuration of krypton. So [Kr] stands for:
1s² 2s² 2p⁶ 3s¹ 3p⁶ 4s² 3d¹⁰ 4p⁶
That's a lot to write down, so it's shortened to [Kr]. When Sal writes [Kr] 5s² 4d¹⁰ 5p² for tin, that means we have 14 more electrons than are found in Krypton and they're in the 5s, 4d and 5p orbitals.
Finally, I am getting this. Thank you Dr. Khan!
@ligitcounterfit no he meant to say as the atom gets larger
What you're saying makes sense, but my textbook says that electrons are categorized into 3 groups. The inner electrons, the outer electrons, and the valence electrons. for main group elements the outer electrons are the valence electrions. but for the transition elements, all the (n-1) d elections are the valence electrons, and the outer electrons are those in the highest energy level (the highest n value)
they use 8 because it takes more energy to open up a new shell, when their are 8 the electrons won't jump to other atoms to either get rid of or aid the extra electrons so its more stable and balanced
In the Kaplan mcat book, every outter electron regardless of energy level is a valence electron. So for example Ir would have 2 s valence electrons and 7 d valence electrons for a total of 9
Great video. I liked it very much. More capturing then other professors I had to listen. The language is easy an not so boring. Thank u.
Are we going to pretend like Sn isn't Tin?
hahahaha you had me gasping..
Minenhle Zukula Zama i am shook! I noticed too.
Look it up pls
Minenhle Zukula Zama
No way...
Minenhle Zukula It is tin but its Latin name is stannum dats y the chemical symbol is sn
Thank you so much for this, after listening to your lesson on the periodic table I am now understanding this better than having two science teachers explain this configuration.
@clemens2003 The rule is a function of the nuclear size, and the distance of the outer shell to the nucleus. It's simply that 8 electrons in the outer shell is more stable. That's when all forces are in balance. (atomic, magnetic, strong, weak, gravity) For star systems, the distances are so great that only one force is involved, gravity. The orbiting bodies will configure for lowest energy state for gravity. Also the bodies are not uniform, like electrons, protons, and neutrons.
you are the best khan. i am so glad to know you
it worked perfectly in my undergrad classes, and follows my book's descriptions as well.
had not ever gone this far - teachers literally orchestrated me away from science classes
I like Khan Academy but honestly I barely learned anything from this video mainly cuz you keep moving from topic to another topic but nonetheless thanks for educating me!!
@khanacademy
I think you made a mistake at 7:18!
The are exceptions: Chromium and copper:
[Ar] 4s1 3d5 , [Ar] 4s1 3d10
Sir Soap this is why i am always confused by chemistry concept. So many exception in chemistry and lecturer dont even know why. Lol
Silinium! I laughed a bit at that one xD Great videos though, as always!
Great analysis of the Periodic Chart! 😊
Sal, you deserve at least half of my tuition.
Valence eletrons are not only those on the outer shell.
"The valence electrons are instead defined as those outside a noble-gas core"
(Wikipedia: wikipedia(dot)org/wiki/Valence_electron)
wow ur videos helppp soo much i was studying for my chem exam and i had forgotten everything and ur videos helpedd me alot!!!! Thanks a ton
Wait, so Helium has 2 protons and 8 electrons in it's outer shell? Is that correct or am I missing something? I thought an element in equilibrium had the same number of electrons as protons.
Vector Boris
Oh ok, that threw me off, is it usually located in the S block on normal charts? I notice it's colored like the ones in the P block, that crap makes it super confusing!
@Giallorossi03 you guys...the periodic table consist of elements that are named in Latin and Greek. Tin is the English notation for this element. But yeah, it is kinda funny =D
both the lady and Mr.you are good teachers!😊
you make everything make so much sense... throughout these visa i keep having "EUREKA!! moments"
This guy is a boss! Helped me out sooo muchhh!!
Hello:) I'm from Italy..your lessons are really awesome, and your way of teaching isn't as the way of teaching of my chemistry teacher, , thank you so much, i will follow you for all my university career , and please continue to do other lessons of chem, anatomy and biology.. bye bye from Italyyyyyyy :) anyway sorry for my poor English ..and hope to see other lessons on youtube ... !!!!!
Netflix and chill? No thanks, Khan Academy and chill
Thank you so much for this video it answer all my questions. I don't know why my professor wasn't able to explain it this way.
Can you recommend a companion textbook for these videos, preferably free online? It would help with understanding some of the material.
Awsome! Thank you for this beautiful explanation!
Thank you Dr. Khan
I studied Robotics Engineering for 5 years and never heard this explained better.
perhaps you should look up the recent articles by Eugen Schwarz in the Journal of Chemical education. I assure you what I am saying is correct. Most textbooks have it wrong. 3d actually fills before 4s. That's precisely why 4s is preferentially ionized. I have been teaching general chemistry for 30 years, the past 15 to classes of 350-450 students in US colleges, most recently UCLA. I am not a kid off the street just trying to disrupt this website or trying to undermine the amazing Kahn.
Great visualization of back filling
Loving these videos so much! It's all very exciting stuff and appreciate it a lot
More importantly, the 4s orbitals DO NOT fill before the 3d in transition metal atoms.
THis is a common textbook error. The 3d are filled first but the final 2 electrons enter the 4s orbital to minimize repulsion. Please see the blogs on my website on this topic
This was ridiculously helpful, thank you
Dear Prof. Khan, is it possible to write Fe as [Ca]3d6? or would it be better to write it as [Ar]4s23d6 since it shows that 4 is the highest energy shell?
@monkeypenguinftw oh, ok, then how do you find the electrons??
probably best that he's not a 'secret' weapon
You're really great ! thanks you !
btw - you forgot to mention that helium doesn't infact have 8 electrons (it's written under 8)
also wrote that Cu Ag and Au would have 2 electrons in their outer shell although they actually have 1 since they give away 1 to fill their d shell.
But thanks alot !
Hi, as to why d fills n-1 rather than n (5:18) may it be a screen effect : Electron already in place screen the nucleus and allow new electron to be closer with the same energy ?
do you subtract the atomic number from the atomic mass to find the electrons?? how do you find the neutrons?
at 9:50, for Sn, if we ionized it, removing 5p2 and 5s2, and then had enough energy to rip yet another electron off, which electron would go first? In other words, given [Kr]4d10 configuration of Sn, which would be the next electron to be lost? From d orbital?
this is why youtube and the information age we are currently in are so cool.
education is now nearly free
thats because iron can suffer orbital hybridisation, so the iron valence can be 2 or 3
My theory was that D and F electrons had stronger pulling forces towards the nucleus, which somehow leeches kinetic energy and centripetal force from the electron.
$0.02
7:00 it's almost funny how much those '2's look like '1's
wow , you my friend can be a very successful university teacher , you explain this things like an alien , u seem to be very smart :) , thanks a lot for sharing ur wisdom mate
YOU SIR LET ME PASS MY FINALS.
This man's voice is golden
I believe a valence electron is an outer electron, but is UNPAIRED. Hope this helps:-)
So if the electron configuration of Cr is [Ar] 4s^1 3d^5 due to Hund's rule. Then Cr has 1 valence electron right? I'm sure someone already asked this question but it doesn't seem very recent... Thank You
BAdBrAd yes that is so
This video helped me so much thank you!
Nice demonstration! BTW, Sn is Tin.
@PINKmeUP67 It's 7 because the highest energy level is 4. [Ar]4s2 3d10 4p5
The 4s2 and the 4p5 add to 7.
That 3d10 portion is what he was talking about when he mentioned the back filling. Make sense?
Do you have anything on quantum numbers and energy required to to move to another energy shell? I am studying Chemistry.
This guy gets me through AP Chemistry :P
That program is the reason I'm even here watching these videos
what happens when i need to solve in the D groupe for example the one with 72 protons ans 72 electrons or 104 electrons how do you count that one??
CU will have one electron in its outer most shell because it has the electronic configuration of [Ar],3D''10,4S"1
Thanks for the laugh! You made my day.
Thanks it really did help me a lot
Hi. What would be electron configuration for Copper in ground state? and the number of outermost electrons?
That was amazing explanation
lol pause at 3:24 for figures that look like pacman!! how this guy adds video game characters into chemistry i dunno! but it's a win!
Makes perfect sense, thanks!
Can you please do the topic Hybridization?
wow! this is really helpful!! thank you so much!!!
thats a pretty flower you drew
@Breyerlov mass- atomic number .. you always subtract a smaller number from the bigger one ;)
Thank you very much. I can't express how much I need to than you.
02:00 can it also be written as [ca]3d^6, since calcium is the nearest outside of the D-block?
i would rather pay you to teach me than my greek professor here at my college...
what video should i watch before this one? I don't understand some of the material.
12 years to the future. anyway,
s, p, d, and f orbitals can hold 2, 6, 10, and 14 electrons respectively.
idk why 8 is the "stable" amount of valence electrons but if you take the average of the maximum numbers of electrons those orbitals can hold:
2 + 6 + 10 + 14 = 32
32/4 = 8
maybe it has something to do with that?
He did not make that mistake, he only made one mistake which is saying that Sn is Selenium but Sn is Tin, Se is Selenium. He was referring to the electronic configuration of Tin which is [Kr]5s^2 4d^10 5p^2. Because after you count the entire periodic table before Krypton it ends at the 4p^6 and since Sn(tin) is found on the 5th period or 5th energy level it should start with a 5s and not a 4s.
Good question. What did/are u studying Sal? I know this stuff from school but still.
Sal you said in this video that atoms are best paired up when there are 8 electrons on the outside? Does this in anyway to your knowledge, theory, fundamental ideas have any relation to our solar system only having 8 planets? Has this been researched or have any theories been formed?
Just something that crossed my mind today.
A spider has 8 legs, coincidence or conspiracy?
Pretty helpful. The info about the valence electrons was good. But Sn is Tin, not Selenium. That would be Se.
thanks to Sal I now love the periodic table...