Electron Arrangement and the Wave-Mechanical Model

Wave-Model Electron "Filling" Order, Electron Configuration, and Orbital Diagrams

Hello,

This post explains the #Wave-Model electron "filling" order, electron #configuration, and #orbital diagrams. When we think about the arrangement of electrons, it's helpful to imagine that we are "creating an atom from the 'ground' up".  With that in mind, all electron arrangements (configurations) begin with hydrogen, the simplest atom.

Wave-Model Electron "Filling"  Order

The discoverers of the #modern atomic theory found that the arrangement of electrons is somewhat "different" from the Bohr model.  A diagram, below, will be helpful in explaining this.

Note - Left-Click On the Diagram to Display a Larger Image
The Diagram Excludes Principal Energy Levels 6 & 7 (which contain f-sublevels)

As the diagram indicates, each Bohr energy level corresponds to a main (or #principal) energy level which, in turn, are further divided into sublevels.  Each sublevel consists of its own, unique, potential energy and the "spreading" of sublevels (at principal energy level 3 and above) causes highest energy sublevels to "overlap" the lowest energy sublevel of the following higher energy main level.  For example, the 3d sublevel has a higher energy state than the 4s sublevel.  Every element has its own, distinct, arrangement of electrons, which is always "built up" from the lowest energy sublevel (1s) to the highest occupied level of a particular element.  When we consider that the atomic number of an element (taken "straight off" the periodic) is equal to the number of electrons contained in every atom of that element, then we can determine the arrangement of electrons by simply "filling in" electrons from lowest to highest energy, according to the above 'Wave Model' chart.  When each sublevel is "completely filled", then the next higher energy sublevel 'gets' electrons (assuming more electrons are available).

Electron Configuration

The #electron #configuration of an element is a short-hand way of viewing its particular electron arrangement.  Electrons are "filled-in" according to the above diagram, taking into account the maximum number of allowed electrons for each sublevel.  The number of electrons contained in a sublevel is indicated with a superscript.  See some examples, below.

Electron Orbital-Filling Diagram

There is another method which allows one to view electron arrangement in much more detail; The #Orbital Filling Diagram.  The orbital-filling diagram uses "boxes" to represent individual orbitals and a series of boxes in close proximity to represent a sublevel.  Each sublevel series is labeled according to an element's electron configuration.  There is an additional property of electrons shown in the orbital-filling diagram; electron spin.  Electron #spin indicates the "direction" of a magnetic field (North end up or north end down).  Numerically, electron spin is either +1/2 or -1/2.  These opposite electron spins are indicated with up and down arrows.  The following figure shows a commonly utilized model of electron spin.

 
A properly constructed orbital-filling diagram will also demonstrate #Hund's Rule: All orbitals of a sublevel must be singly occupied before they can pair-up.  A sublevel with singly occupied orbitals is at a lower energy state than a sublevel consisting of paired up electrons (Assuming the same number of electrons in both cases.).  When we say, "a sublevel at lower energy", we can also say, "the entire atom is at a lower energy state".

The following image shows examples of orbital-filling diagrams for a number of elements.

The red arrow is there to indicate that all electron configurations begin with Hydrogen!

That's all for this post, finally.  I hope it's helpful!

Have a good one.