https://www.wired.com/story/what-makes-an-element-the-frankenstein-of-sodium-holds-clues/

A few years ago, a group of physicists created an unusual, never-before-seen subatomic particle. Using a particle accelerator at Riken, a Japanese research institute, they slammed streams of calcium nuclei against a metal disk, over and over, for hours at a time. Then, sifting through the aftermath of the collisions, they found their coveted particle. They named their creation: sodium.

That’s right, sodium. Don’t let the familiar name fool you; you’ll never find this object in ordinary table salt. Almost all sodium on Earth is sodium-23, where the number refers to the 11 protons and 12 neutrons that make up its nucleus. Yet those 23 particles do not encompass all that can or could be sodium. Technically, any nucleus with 11 protons is sodium. The periodic table, after all, organizes the elements by the number of protons in their nuclei, and sodium is element #11. That says nothing about the number of neutrons the particle harbors inside.