In my last post, I discussed the geometric nature of each of the four quantum numbers needed to identify each electron in any atom and how those numbers uniquely identify the region of space around the nucleus in which you might find each electron. These regions are called orbitals.

You might have wondered why the periodic table has its shape. No doubt you've learned something about the history of how it all came about by measurements of physical and chemical properties, but ultimately, now that we have a periodic table arranged as it is, let's look at how geometry plays a role in the shape of the periodic table.
 
How do orbitals give the periodic table its iconic shape? Why is there a big gap in the middle?
 
When we talk about the outermost electron, we mean the one farthest from the nucleus. It’s the electron that will likely be the first to interact with electrons in a different nearby atom. In fact, electron interaction is one of the most foundational aspects of Chemistry! This is one of the reasons why it’s so important to think about the geometric properties that make up the orbital associated with the outermost electron in each atom.
 
The shape of the outermost electron orbitals give the periodic table its shape! Look at the image carefully. The outermost electron orbital of the first two columns is a sphere and are called s-orbitals.

The six right-most columns of the periodic table have outermost electron orbitals that look like two eggs – or a dumbbell if you like – and are called p-orbitals.

The “middle” ten columns have up to four egg shaped regions including a single torus ring and are called d-orbitals.

The lower two rows – that actually form the region of the periodic table squeezed between the spherical s-orbitals and the four-egg shaped d-orbitals? These orbitals have up to six- and eight-packs of egg shapes including two torus rings. These complex shapes are all  f-orbitals.
 

We could get into details about things like why helium (He) is usually positioned at the top of the right-most column or how about 20 of the atoms on the periodic table have outermost electrons that violate this broad geometric pattern, but the physical properties that support those reasons come from the geometric nature of these orbitals. So, we’ll stop right here and let you think a lot more about how the geometric properties (quantum numbers, n, l, m, and s) give the SHAPE of the outermost electron orbitals and how these shapes give rise to the arrangement of the entire periodic table of elements.
 
Oops. I used the word “elements." What's the difference between an atom and an element? I’ll leave it to you to find out. Meanwhile, think about how geometry is indeed at the very foundation of the periodic table. It’ll help you think more about how atoms are arranged than mindlessly reciting silly songs to memorize element names.