All elements on the periodic table are pure substances.

Here's why:

* Elements are the simplest forms of matter. They cannot be broken down into simpler substances by chemical means.

* A pure substance contains only one type of atom. For example, a sample of gold contains only gold atoms, a sample of oxygen contains only oxygen atoms, and so on.

However, it's important to note:

* Elements can exist in different forms: For example, carbon can exist as diamond, graphite, or fullerene. While these are different forms of carbon, they are still pure elements because they contain only carbon atoms.

* Elements can be combined to form compounds: For example, water (H₂O) is a compound made of the elements hydrogen and oxygen. Compounds are not pure elements.

So, while all elements are pure substances, it's essential to understand that elements can exist in different forms and can be combined to create new substances.