A pure covalent bond occurs between two atoms of the same element. This is because the electronegativity (the ability of an atom to attract electrons) is identical, leading to an equal sharing of electrons.

Here are some examples:

* H-H (hydrogen molecule)

* O=O (oxygen molecule)

* Cl-Cl (chlorine molecule)

* N≡N (nitrogen molecule)

Let me know if you'd like more examples!