Rubidium is element number 37, a metal with the symbol Rb. Its name comes from the Latin word for “dark red.”
Atomic number 3785.47
RbRubidiumルビジウム (rubijiumu)
Symbol
Rb
Atomic weight
85.47
Place in the table
Period 5 · Group 1
Atomic weight from the Chemical Society of Japan, “Table of Standard Atomic Weights with Four Significant Figures (2026)”.
Found by the color of light
Rubidium was found from a dark red line (an emission line) seen when light is split finely, and it was named for that color. This was in 1861.
A year earlier, in 1860, caesium had been found in the same way, from a “sky-blue” line.
Where it sits on the table
Rubidium is in the fifth row of Group 1, the same column as lithium, sodium and potassium. Directly below it is caesium.
Think about it
Q1Why can studying the color of light reveal a new element?
Q2Look for elements named after colors.
Q3Do you think rubidium is like sodium and potassium in the same group?
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 emission lines include rubidium (dark red), caesium (sky blue), indium (indigo) and thallium (green).