Rubidium (Rb)
Rubidium is element 37, an alkali metal in group 1, period 5. A neutral atom has 37 protons, 48 neutrons and 37 electrons, 1 of them valence electrons.
Alkali metal- Atomic number
- 37
- Atomic mass
- 85.468 u
- Valence electrons
- 1
- Protons · neutrons
- 37 · 48
- Electrons per shell
- 2, 8, 18, 8, 1
- At room temperature
- solid
Bohr model of rubidium
The Bohr model draws rubidium as a nucleus of 37 protons and 48 neutrons, with its 37 electrons on 5 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 8 in shell 4, 1 in shell 5. Press Build the atom to watch the shells fill from the inside out. The outer ring (the O shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of rubidium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹
Short form (noble gas notation): [Kr] 5s¹. The [Kr] stands for the electrons of krypton, the noble gas before it.
How many valence electrons does rubidium have?
Rubidium has 1 valence electron.
Rubidium is in group 1, so it has 1 valence electron. It tends to lose that electron and form a +1 ion.
Protons, neutrons and electrons
| Protons | 37 | equal to the atomic number |
|---|---|---|
| Electrons | 37 | equal to the protons in a neutral atom |
| Neutrons | 48 | mass number 85 − 37 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Rubidium properties
| Symbol | Rb |
|---|---|
| Category | Alkali metal |
| Group · period · block | 1 · 5 · s |
| Atomic mass | 85.468 u |
| State at 25 °C | solid |
| Melting point | 312.5 K (39.3 °C, 103 °F) |
| Boiling point | 961 K (688 °C, 1,270 °F) |
| Density | 1.53 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Atomic radius | 303 pm |
| First ionization energy | 4.177 eV |
| Electron affinity | 0.468 eV |
| Oxidation states | +1 |
| Common ion charge | +1 |
| Discovered | 1861 by Robert Bunsen |
Where rubidium sits on the periodic table
Group 1: Hydrogen, Lithium, Sodium, Potassium, Cesium, Francium.
Questions about rubidium
How many valence electrons does rubidium have?
Rubidium has 1 valence electron.
How many protons, neutrons and electrons does rubidium have?
A neutral rubidium atom has 37 protons and 37 electrons. Its most common form has about 48 neutrons (mass number 85 − 37 protons).
What is the electron configuration of rubidium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s¹, written in short form as [Kr] 5s¹.
What does the Bohr model of rubidium look like?
A nucleus of 37 protons and 48 neutrons, circled by 5 electron shells holding 2, 8, 18, 8, 1 electrons.
What is the atomic number of rubidium?
37. The atomic number is the number of protons in the nucleus, and it is what makes an atom rubidium.