★ Thallium (Tl) ★

An Amazing Learning Experience About An Element!

All About Thallium ★

On the right is a Bohr model of a Thallium atom!

  • Thallium's element symbol is Tl (uppercase T, lowercase L), which is located in the middle of its box.
  • Thallium's mass number is 204.383; it is located directly underneath its element symbol.
  • Thallium's atomic number is 81, because it is located directly above its element symbol.
  • Thallium has 81 protons. When you look at the atomic number, it tells you the amount of protons and electrons.
  • Thallium has 123 neutrons. To find the amount of neutrons, you have to subtract the (rounded) mass number from the atomic number. 204 minus 81 is 123, meaning there are 123 neutrons.
  • Thallium has 81 electrons, because the atomic number tells you the amount of both protons and electrons separately.
  • Thallium is located in Period 6; the Periodic Table is organized with groups (vertical) and periods (horizontal) based on what traits they share with other elements. In this case, Thallium would be located in the sixth row because it has 6 rings in its atoms.
  • Thallium is located in Group 13; it is located in the thirteenth column because it shares multiple traits with the elements in the same group. The Periodic Table is organized with periods (horizontal) and groups (vertical).
  • Thallium is a metal, because it is grouped with the other metal elements and fits the characteristics of a metal; it is ductile (can be hammered into wires), malleable (ability to be hammered), shiny, a conductor of heat/electricity, and a solid.


  • Thallium has 3 valence electrons out of its 81 electrons on its outer rings, because it is in group 13. All you would do is drop the 1.
  • Thallium's reactivity is not stable, but not too reactive either. Thallium is not a noble gas (group 18), so it isn't stable. However, Thallium is not in groups 1 or 7 (but in group 13), which are the most reactive, so it isn't super reactive either.

Other Fun Facts ★

On the left is a picture of the element Thallium!

  • Thallium is typically found in soil and some select minerals (in small amounts).
  • Thallium is used to make some medical agents, electronics (photo-resistors, infrared optical equipment, etc.), rodent killers, and hair removal products.
  • Two elements with similar chemical and physical properties to Thallium are Aluminum and Gallium, because they are in the same Group (on the Periodic Table). Elements in the same group share lots of properties.
  • FUN FACT #1: Thallium is a toxic metal and can cause cancer (when you come in direct contact with it).
  • FUN FACT #2: Thallium was discovered by William Crookes (a British chemist) in 1861.

By Kyra Miller and Anika Sultana, Period 6