Thallium is element number 81, a metal with the symbol Tl. Its name comes from the Greek for “a young green shoot.”
Atomic number 81204.4
TlThalliumタリウム (tariumu)
Symbol
Tl
Atomic weight
204.4
Place in the table
Period 6 · Group 13
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Green light
Thallium was discovered in 1861 and named for the green color it gives a flame (its flame color). Rubidium was found the same year from a dark red line.
Where it sits on the table
Thallium is in the sixth row of Group 13, with indium (indigo) above and gallium above that. Both indium and thallium are named for the color of their light.
Think about it
Q1Picture the green of a new shoot or young leaves. What name would suit it?
Q2How is identifying elements by the color of light related to fireworks?
Q3Can you name the Group 13 elements from the top?
There is no single right answer. Talking it over with someone at home is a good way to learn.
Did you know? — Elements named for the color of their light are spread across the table: rubidium and caesium in Group 1, indium and thallium in Group 13.