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# Shells, subshells, and orbitals

The electrons in an atom are arranged in shells that surround the nucleus, with each successive shell being farther from the nucleus. Electron shells consist of one or more subshells, and subshells consist of one or more atomic orbitals. Electrons in the same subshell have the same energy, while electrons in different shells or subshells have different energies. Created by Sal Khan.

## Want to join the conversation?

• What is the difference between Shells, Subshells and Orbitals?It was very hard for me to visualize them in my head.How is the 2p6 orbital closer to the neucleus than the 3s2 orbital?Isn't the s orbital always closer to the neucleus?
• An orbital is a space where a specific pair of electrons can be found. We classified the different Orbital into shells and sub shells to distinguish them more easily. This is also due to the history when they were discovered.

Start with the easy. Imagine shells around the nucleus, that get bigger and bigger. The smallest, nearest to the nucleus is shell number 1. It's the one with the lowest energy. Then comes shell number 2, and so on.

Now let's have a look at each shell in detail. They are decided into several subshells. They are the different kinds of orbital. So in the first shell there is only one subshell, the s orbital. It is called 1s.

In the second shell there are s and p orbitals. But the 2s is of course further away from the nucleus, because it is in the second shell. Them comes the third shell even further away from the nucleus. In the third shell we again find p and s orbitals.

The 2p orbital is closer to the nucleus than the 3s orbital, because it is in the second shell, which is closer to the nucleus than the third shell.
• helium's electronic configuration is 1S^2 but then why it is in P block ????
• It's not really in the 'p' block. It's there because it has properties similar to the 'p' block elements. The periodic table is organized according to properties, not orbitals.
• At Sal says that you could find the electron anywhere. Does that mean that it could be 200 km away from the nucleus (even if with a very small probability) or is there a limit for the distance?
• It's a strange reality where it's possible for a part of me to be 200 km away from me, even if the probabilities are as low as they are.
• If the s sub-shell has only one orbital then what does 1s^2 2s^1 mean?
• What I understood is that the notation basically tells you this:
-the first number is the number of shell;
-the letter is the type of orbital;
-the index means how many electrons the orbital contains.
Therefore,
1s^2 means that there is orbital s with 2 electrons in shell 1 .
2s^1 is s orbital with 1 electon in shell 2.
I'm not very good at explaining, but I hope you got it!
• How are orbitals arranged in an atom?
How can one imagine the structure of a real atom not one which bohr model suggests but an original one observed by solving the wave equation...
how can one* assemble* all four quantum number and get the orbitals, subshells structures?
How do Atomic orbitals overlap among each other inside an atom and between the molecules?
I would be pleased if someone can really help me imagine an atom........thank you in advance.
• Alright, well let's start with the electrons first. Electrons move around in "quantized" energy states. Meaning they exist in a specific energy state, and can be anywhere at any given time in that orbital due to the heisenberg uncertainty principle. Think of "quantized" as the smallest units of energy states a particle can have. In comparison think of a basketball it moves in a very fluid motion as it rolls on the ground, now electrons move in a step wise manner on a "ladder" of quantum energy states. They cannot move in a very fluid motion, because distances are so small at that scale.

So if you were trying to imagine an atom, if you looked at the atom from the outside you would see a fuzzy cloud.

Of course atoms have many electrons so you have various electrons in different energy quanta states orbiting around the nucleus.

The nucleus it self would be extremely small in comparison to the electron cloud.
• If Helium can't combine with other elements, In the composition of sun how does it combine with Hydrogen?
• Usually in chemistry we're concerned with chemical reactions. Reactions where the valence electrons of atoms interact to form new chemicals by breaking and forming chemical bonds. Helium doesn't really react chemically because its valence shell is filled and it is stable in its natural electron configuration.

In the sun we don't really have chemical reactions involving helium, rather nuclear reactions. Nuclear reactions are different from chemical reactions in that chemical reactions only involve the electrons of atoms and do not touch nuclei of atoms where we find protons and neutrons while nuclear reactions involve the nuclei of atoms. Essentially what happens in the sun is that atoms of hydrogen-1 (that is isotopes of hydrogen with a single proton only) collide into each other with such force that they fuse into new atoms. The main nuclear reaction occurring in the sun are series of nuclear reactions called the proton-proton chain (because it begins with the collision of two hydrogen atoms containing a single proton each) which eventually results in helium atoms.

But once helium is formed, it doesn't really combine with hydrogen afterwards in either chemical or nuclear reactions. So in the sun it isn't really a case of helium combining with hydrogen in a reaction sense, rather they are just in close proximity to each other in a mixture.

Hope that helps.
• Why is it said that there are 2 electrons in the least energy 1s shell (won't they repell each other ? ) or is it because the attraction and repulsion balance between the core protons and surrounding electrons is best satisfied by this theory?
but still why just 2... why not 4 or maybe 24(random )??
• The electrons repel each other but they are also attracted toward the nucleus by the positively charged protons.

The reason 2 is the magic number for the innermost shell lies in the laws of quantum mechanics, which are extremely complex and not intuitive at all. The best way to think of it for now is just that each shell has a certain capacity, and the maximum capacity of the innermost shell is 2. Then the next 2 shells hold up to 8 electrons. Then the next can two hold 18, then after that its 32.
• I keep re-watching these videos and looking online but, I do not understand anything when he is explaining shells. Mostly the way periods work. what does 1s1 stand for? then 1s2 1s1? what are these numbers and S identifying?
• The first number tells you the energy level of that orbital, or shell if you want to call it that. 1 is first shell, 2 is second shell etc.
The letter tells you which orbital it is, eg s, p, d or f
The superscript number tells you how many electrons are in that orbital

1s^2 means 2 electrons are in the 1s orbital
1s^2 2s^2 2p^6 means 2 electrons in the 1s orbital, 2 electrons in the 2s orbital. and 6 electrons in the three 2p orbitals
• Why can`t we determine the exact position of the electron?
• because it is microscopic and when it comes to microscopic particles the Newtonian Physics or classical physics fails we can't apply it on microscopic particles because of particle and wave duality. Only on Macroscopic particles we can apply classical physics because it largely shows particle nature and their wave nature can be neglected because they have very less detectable waves. when it comes to microscopic particles we have to consider its wave nature because their waves can't be neglected they have pretty detectable waves
• If the orbitals are perfect spheres, shouldn't the energy of the orbitals reduce as we move further away from the center?
Because the pull from the center is less, hence it would require little energy to balance out the pull.