Radioactive elements tend to be located in two main “places”:

  1. in nature , inside certain rocks, soils, water, and even the air, and
  2. on the periodic table , mostly toward the heavier end (high atomic numbers).

Natural locations (on Earth)

In the real world, naturally occurring radioactive materials are spread almost everywhere but usually in very tiny amounts.

Common places they tend to be found:

  • Rocks and soil
    • Elements like uranium, thorium, and potassium-40 are mixed into the Earth’s crust.
    • Some rocks (like certain granites and uranium ores) have higher concentrations, so they are more radioactive.
  • Sand and sediments
    • Beach sands and other sediments can contain minerals rich in radioactive elements, especially where heavy mineral sands occur.
  • Groundwater and drinking water
    • Uranium and radium can dissolve into groundwater, so low levels can show up in wells and sometimes in tap water.
  • Air (as radon gas)
    • Uranium and radium in the ground decay and release radon, a radioactive gas that seeps up into basements and buildings.
  • Everyday materials and products
    • Small amounts of natural radioactivity appear in things like building materials (brick, concrete, granite countertops), coal ash, some fertilizers, and even tobacco products.

A simple picture: if you’re standing in a house made of brick or concrete on rocky ground, you are surrounded by tiny amounts of natural radioactivity from the soil, the building materials, the air, and even your food and water.

Where they sit on the periodic table

On the periodic table, radioactive elements are not all in one single block, but many of them cluster toward the heavy, high‑atomic‑number end.

Key patterns:

  • Very heavy elements are almost all radioactive
    • Elements with high atomic numbers (like uranium, thorium, plutonium and beyond) are unstable and tend to undergo radioactive decay rather than stay in one form forever.
  • Actinides row (bottom row of f-block)
    • Many radioactive elements sit in the actinide series (from thorium through lawrencium), which is usually shown as the second of the two “floating” rows under the main table.
  • Some lighter elements are also radioactive
    • There are naturally occurring radioactive isotopes of lighter elements too (for example, carbon-14, potassium-40), but the classic “radioactive elements” you hear about in nuclear power or weapons are typically the heavier ones like uranium and plutonium.

So, if you look at a periodic table: you’ll tend to find the strongly radioactive elements among the heaviest atoms, especially in the actinides and the elements beyond lead.

Quick classroom-style answer

If this is for a quiz or homework, a concise answer could be:

Radioactive elements in nature are mainly found in certain rocks, soils, groundwater, and in radon gas from the ground, and on the periodic table they tend to be located among the heavier elements, especially in the actinide series near the bottom right.

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