Rubidium (Rb)
Element 37 · Alkali metal · Solid at 25 °C · Group 1, Period 5
Rubidium is so reactive it ignites in air, yet its steady atomic vibrations help keep time in atomic clocks and GPS satellites.
On the periodic table, rubidium sits in group 1 — the alkali metal group — in period 5. It is one of 6 elements classified as an alkali metal, and at room temperature (25 °C) it is a solid.
The alkali metals are soft, silvery metals with a single electron in their outer shell — which they give up so easily that they are among the most reactive metals known. They react vigorously (sometimes violently) with water, tarnish in air within minutes, and are never found as free metals in nature. In the lab they are stored under oil to keep air and moisture away. Reactivity increases as you move down the group.
Properties of rubidium
| Atomic number (Z) | 37 |
|---|---|
| Symbol | Rb |
| Atomic mass | 85.468 |
| Category | Alkali metal |
| Group | 1 |
| Period | 5 |
| Block | s-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Kr] 5s1 |
| Electronegativity (Pauling) | 0.82 |
| Melting point | 39.31 °C (312.46 K / 102.76 °F) |
| Boiling point | 688 °C (961.15 K / 1,270.4 °F) |
| Density | 1.532 g/cm³ |
Position in the periodic table
Rubidium shares group 1 — the alkali metal group with Hydrogen (H), Lithium (Li), Sodium (Na), Potassium (K), Caesium (Cs), Francium (Fr). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Rubidium melts at 39.31 °C (312.46 K / 102.76 °F) and boils at 688 °C (961.15 K / 1,270.4 °F), giving it a liquid range of about 648.7 °C at standard pressure.
Its density is 1.532 g/cm³.
See also: the interactive periodic table, how to read the periodic table, the element families tour.