why the atom's first orbit contains only 2 electrons and second orbit has only 8 electrons and why not more ?

Answer 1

Here's the watered-down high school version...it gets more complex than this.

Electrons are lazy. They will go where it costs them the least amount of energy. In the first energy level, the electrons are quite close to the nucleus. Remember that electrons repel each other and want to be as far away as possible. Because it is such a small space, it would require much more energy to put a third electron there than it would to just put the electron into the second energy level. The second energy level has a bit more room, so you can fit 8 electrons in this level before it becomes too "expensive" and the electrons start filling the third level.

Answer 2

Quantum theory determines it.

A particle exhibiting wavelike properties should be describable by a mathematical equation called a wave function and denoted by the Greek letter psi.

The equations require three variables: the distance of the point from the nucleus, r. The angle between z-axis and the line connected the nucleus and the point, theta q. The angle between x-axis and the line connected the nucleus and the point, phi f. All those factors HAS TO be taken into account, NOT JUST THE DISTANCE!!!!!

y(r, q,f) = R(r)Y(q,f)

The function R is called the radial wave function; the function Y is called angular wave function. Quantum number n and l will affect function R; Quantum number l and ml will affect function Y.
Quantum Number and Electron orbitals. I will take about those quantum numbers later.

To let those equations make sense, we have to define a few numbers.

The first quantum number n is called principal quantum number. It can only be a positive, nonzero value. The second quantum number l is called angular momentum quantum number. It may be zero or a positive number, but not larger than n-1. This number determines the type of shells. The third ml is the magnetic quantum number. It may be a negative or positive integer, including zero, and ranging from –l to +l. ml determines the number of orbitals in each shell.

All orbitals with the same value of n are in the same principal electronic shell or principal shell, and all orbitals with the same value of n and l are in the same subshell.

Three fundentmental principles about electron configuration,

Aufbau Principle:
as protons are added one by one to the nucleus to build up the elements, electrons are added to the available orbitals in order of increasing orbital energy. Electrons occupy orbitals in a way that minimizes the energy of the atom. ["the lazy theory" ppl mentioned]

The Pauli exclusion principle:

No two electrons in an atom may have all four quantum numbers alike. Only two electrons may occupy the same orbitals and must have opposing spins.

Hund’s Rule:
When orbitals of identical energy (degenerate orbitals) are available, electrons initially occupy these orbitals singly. It takes energy to pair electrons.

So, from all those theories above, for the first "atomic orbital" (we'd like to call it shells) in your case, n = 1, so l = 0; and ml falls within [0,0] and can only be an interger, so ml = 0. So, there is only one shell, only one orbital. That's why the first shell can only hold 2 electrons.

The second shell, n = 2, l has to be non-zero integer and less than or equal to 1, so, l could be either 0 or 1; when l = 1, ml falls within [-1, +1], so ml could be -1,0,+1; when l = 0, ml could be just 0. So, in total, there are four diffenent atomic orbitals here, according to quantum theory, each holds two electrons, in total can hold 8 maximum.

Answer 3

Ah yes. The "here's the textbook answer" people spilling forth the trivial pursuit answers of quantum mechanics, aufbau, hunds, exclusion principle and all that other jazzy jazz stuff that no one even thinks about any more.

As yourself a question: If electrons are discrete particles (quantum mechanically represented by wavefunctions), then what symmetry properties do they exhibit when confronted with a central field (nucleus)? This nonsense about the exlusion principle and Hund's rule and all that -- purely convenient guides based upon observations, experiments, quantum mechanical theories -- DFT, Hartree Fock and the like. But NONE produce exact results but for few systems and all are purely approximations at best.

Why do only 2 electrons form the first shell? Do you really think it's because the spin-spin interaction requires them to be up-down pairs to prevent two electrons from being "in the same state"? Does that otherwise mean that the electrons are 100% interacting -- are they atop eachother in precisely the same spatial location? No. So how are they in the same state again?

But your textbook answer, recited like a boyscout, is just 1s shell is spherically symmetry due to the wavefunctions of two electrons being in the same state, 'forced' by Pauli to have distinct characteristics -- so one is spin-up, one spin-down. The next 'shell' is 2s+2p, with 2s a distinct pair, and 2p with two pairs along three different axes (px, py, and pz) which supposedly follow pauli's exclusion idea.

But it's the symmetry of charge particles. Trust me on this one.

Answer 4

because the 1st level only has the energy required to hold 2 electrons. Since the 2nd is a little farter away from the nucleus can hold more electrons. The formula to find out the nuber of electron "n" orbital can hold is
2n. be aware that the 2nd two is an exponent. Fucker

Answer 5

There are 2 innovations to this, reckoning on regardless of once you're speaking about atomic stability or chemical stability by which i anticipate you intend reactivity. Atomic stability has now no longer something to do with the fashion of electrons yet is to do with how very extremely the nucleus will breakdown or decay into atoms of shrink atomic quantity. The outer electron shell many cases determines the chemical nature of an element. If the outer shell is stuffed with electrons the component is chemicaly good and unreactive, (He, Ne Ar, etc.) For the distinct aspects the stability is to now no longer do with even or unusual numbers yet how actual the component will settle for or donate electrons to type a bond with yet another component. there are a range of of aspects in contact and are often quantified in phrases of ionisation skill and electron affinity. i advice you study texts on the Periodic table and any good e book on Inorganic Chemistry.

Answer 6

It also has to do with kinetic and potential energy of that particular orbital. All electrons want to get as far away from the center as possible so that their evergy will increase. Remember, all atoms want to abide by the octet rule and fill their valence electrions too. In a nutshell, everyone is trying to be a noble gas.

Answer 7

Why are there 360 degrees in a circle and why is force of gravity 9.8m/s^2? That's just the way it is. Since electrons repulse each other, and they are in a sort of "cloud", there are only so many electrons that can fit in each orbit.

Answer 8

I think it has to do with the amount of energy available in each energy level. As an analogy, imagine a rope attached to a fixed object at one end, and attached to a motor that moves up and down on the other. The motor has discrete energy settings (like a knob that clicks into each position rather than turning smoothly). In the lowest setting, you get two standing waves, and at the next setting you get eight. I don't think the analogy is exactly right, but that's the way I think about it.

Answer 9

because thats all it will hold. if the atom has only 2 electrons like helium the atom is stable in the first level. scientists really dont know why but that is just the beauty of nature. it cant be explained.

Answer 10

because there is one formulae for that (2*n*n)where n is 1 2 3
i.e first orbit second orbit like that