Atoms.... why cant an atom have more than two....

Question

eletrons in the first energy level and so on. is there a limit to how many electrons an atom can aquire?

Answer 1

Because of the Pauli exclusion principle, no more than two electrons may exist in a given atomic orbital.

Answer 2

Don’t understand the question. A hydrogen atom only has one electron.

And for Pete WG, freewill, Norrie and David

Then why does a hydrogen atom have only one electron?

Maybe I’m thick and don’t understand. But why?

Answer 3

This has all been calculated and experimentally worked out by atomic physicists...etc..

The following shows the Maximum number of Electrons possible in each Energy Shell.

K..2 x 1²..= 2

L..2 x  2²..= 8

M..2 x 3²..= 18

N..2 x 4²..= 32

O..2 x 5²..= 50  *

P..2 x 6²..= 72  *    

Q..2 x 7²..= 98  *          

* = Theoretical Capacity

And, despite the thumbs down merchant, this is as correct as you will get.

Answer 4

The physics of atomic electrons is described by the mathematics of quantum mechanics. The Austrian mathematician Erwin Schrodinger and the German physicist Werner Heisenberg developed this non-classical theory, during the nineteen-twenties. The electrons, around the nucleus of an atom, and their interaction are described by a nuclear potential well and the electron's quantum numbers. The quantum numbers are: - the principal quantum number (which gives the electrons orbital shell), the azimuthal quantum number (or angular momentum, which gives the electron’s sub-shell position), the magnetic quantum number, (which, gives the projection of the angular momentum along a specific axis), and the spin projection quantum number. Just as the energy of the electrons  is quantised, and can only change in whole quantum steps, so too are the quantum numbers. The spin projection quantum number is quantised in half units (ms = −1/2 or +1/2), and represents the intrinsic angular momentum of the electron. Because electrons have a half integer spin, they are referred to as fermions.

This non-classical  '...spin refers to a non-classical kind of angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its centre of mass about an external point. A particle's spin is essentially the direction a particle turns along a given axis, which in turn can be used to determine the particle's magneticism. Although this special property is only explained in the relativistic quantum mechanics of Paul Dirac, it plays a most-important role already in non-relativistic quantum mechanics, e.g., it essentially determines the structure of atoms.

In classical mechanics, any spin angular momentum of a body is associated with self rotation, e.g., the rotation of the body around its own centre of mass. For example, the spin of the Earth is associated with its daily rotation about the polar axis. On the other hand, the orbital angular momentum of the Earth is associated with its annual motion around the Sun.

In fact, in classical theories there is no analogue to the quantum mechanical property meant by the name spin. The concept of this non-classical property of elementary particles was first proposed in 1925 by Ralph Kronig, George Uhlenbeck, and Samuel Goudsmit; but the name related to the phenomenon of spin in physics is Wolfgang Pauli...' (Wikipedia).

About two years before Heisenberg published his matrix mechanics version of quantum mechanics (1926), Wolfgang '...Pauli proposed a new quantum degree of freedom (or quantum number) with two possible values, in order to resolve inconsistencies between observed molecular spectra and the developing theory of quantum mechanics He formulated the Pauli exclusion principle, perhaps his most important work, which stated that no two electrons could exist in the same quantum state, identified by four quantum numbers including his new two-valued degree of freedom. The idea of spin originated with Ralph Kronig. Uhlenbeck and Goudsmit one year later identified Pauli's new degree of freedom as electron spin...' (Wikipedia).

Hence, to answer your question - because an electron can has a spin of +1/2 or -1/2 and, according to the Pauli exclusion principle, no two electrons can have the same quantum address - only two electrons can occupy the first energy level of an atom (one electron with spin +1/2 and the other with spin -1/2).

This quantum pairing allows atoms to have many hundreds of electrons in increasing energy levels but for nuclei with more than Z=88 protons radioactive instability sets in. For example, element Z= 114, A =289 or Ununquadium has a half-life of 2.6 seconds and element Z=118, A = 294 or Ununoctium has only been observed as three rapidly decaying, unstable atoms. Hence, nuclear instability, in the very heavy nuclei, limits the number of atomic electrons.  

Answer 5

Pauli Exclusion Principle - 1 spin up and 1 spin down.