Calcium, copper, and bromine are all elements on the periodic table. This means they are pure substances that cannot be broken down into simpler substances by chemical means.

Here's a breakdown of their commonalities:

* Found on the Periodic Table: They all have their own unique position on the periodic table, with different atomic numbers and properties.

* Composed of Atoms: They are all made up of atoms, the smallest unit of an element.

* Can form Compounds: They can all combine with other elements to form compounds. For example, calcium forms compounds like calcium carbonate (found in limestone), copper forms compounds like copper sulfate (used in fungicides), and bromine forms compounds like sodium bromide (used in photography).

Let me know if you'd like to know more about any specific element!