Most sources agree that there are about 38 elements in the periodic table that have no stable isotopes and are therefore always radioactive , but only around 28ā€“34 of these occur naturally on Earth , depending on how ā€œnaturalā€ is defined.

Quick Scoop

Short, direct answer

  • If you mean ā€œelements on the periodic table that are inherently radioactive (no stable isotope at all)ā€, the commonly quoted number in teaching resources is 38 radioactive elements.
  • If you mean ā€œradioactive elements that actually occur in natureā€, modern references give about 28ā€“34 natural radioactive elements , with the count changing slightly based on whether you include all decay products and cosmogenic isotopes.

Why the numbers differ

  • 38 radioactive elements : This count comes from school-level chemistry explanations that list all elements which lack any stable isotope and are therefore always radioactive, including many manā€‘made transuranium elements.
  • 28ā€“34 natural radioactive elements :
    • One detailed reference lists 28 naturally occurring radioactive elements that have longā€‘lived ā€œprimordialā€ radionuclides still present since before the Solar System formed.
* Another chemistry source notes **around 34 radioactive elements occur in nature** , adding some shortā€‘lived decay products and isotopes made by cosmic rays.

How to phrase it in your own work

If you need a clean line for homework, a blog, or a forum post, you can safely write something like:

In modern chemistry, about 38 elements in the periodic table have no stable isotopes and are therefore always radioactive, but only roughly 30 of them occur naturally on Earth.

Tiny extra context (for curiosity)

  • Famous natural radioactive elements include uranium, thorium, radium, polonium, radon, and francium.
  • The very heaviest elements (like oganesson, tennessine, livermorium) are all synthetic and highly radioactive , surviving only fractions of a second before decaying.

TL;DR:

  • Always radioactive elements (no stable isotopes): about 38.
  • Naturally occurring radioactive elements on Earth: about 28ā€“34 , depending on definition.

Information gathered from public forums or data available on the internet and portrayed here.