Where are electrons located according to modern atomic theory?

Answer 1

I hate these kinds of questions, because the mental picture most people have of atoms is so very wrong it's hard to know where to start.

When talking about electrons in atoms, the first thing to know is that they're in orbitals, which are not at all the same thing as orbits. They're not going around and around in circles, they're... somewhere inside a sort of "cloud", and are more likely to be found in some regions of the "cloud" than in others.

There are equations that describe the probability of finding an electron in a given orbital at a particular point in space. These equations are called "wave functions," and are pretty complicated. If you really want to know, I recommend two books in particular: either Levine's Quantum Chemistry (better if you're approaching things from the chemistry side and/or want all the details at an advanced level) or Feynman's Lectures on Physics, volume III (better if you want more of an overview at a college sophomore physics level, or are more of a physicist). Both of these will be in any good college library, and may be in some public libraries with better-than-average science sections (the Feynman in particular).

Multiplying these equations in a particular way and integrating them gives you the probability density... how likely it is to find an electron to be in a particular region. The interesting thing about these probabilities is that they have nodes... regions of space where it's actually impossible to find the electron, though it could potentially be found on either side. For example, a p-type orbital has a nodal plane. The electron can be above the plane or below the plane, but (and this is the part that gives most people conniptions, the first time they run across it) it can never be found in the plane itself. Not even briefly. Not even "just passing through." So how does it get from one side to the other? It... just does. And all the math works out. But to really understand it, you've got to forget pretty much everything you think you know about how the universe works, and learn to trust the math.

Answer 2

The modern atomic theory is based on quantum mechanics.

It states that electrons in the atom are located in orbitals that can contain at most 2 electrons of opposite spin.

These orbitals have no well-defined volume and the electrons do not follow defined trajectories through the orbital they reside in. The behavior of the electrons in an orbital is purely probabilistic and they can be anywhere in it at any instant.

When you see pictures or drawings of the shapes of orbitals they are the "50% probability volume", each electron in that orbital has a probability of 50% of being anywhere inside that volume and a probability of 50% of being anywhere outside that volume.

In very large atoms, the innermost s orbital is "compressed" enough and the nucleus is large enough that there is a significant probability that an electron in that orbital will actually be inside the nucleus. This can allow such electrons to be captured by protons in the nucleus, converting them to neutrons in a process called K Capture (a form of Beta Decay).

The 1st shell consists of only one s orbital.

The 2nd shell consists of one s orbital, and three p orbitals.

The 3rd shell consists of one s orbital, three p orbitals, and five d orbitals.

The 4th shell consists of one s orbital, three p orbitals, five d orbitals, and seven f orbitals.

The 5th shell consists of one s orbital, three p orbitals, five d orbitals, seven f orbitals, and nine g orbitals.

The only electrons in the atom that participate in chemical reactions (the valence electrons) are those in the s and p orbitals of the outermost shell.

Answer 3

In orbitals or three-dimensional representations of probability density obtained by solving wavefunctions.

Answer 4

electron cloud

Answer 5

In orbit around the nucleus.