Cesium (Cs)
Cesium atomic clocks are used to define the length of one second.
Cesium properties
- Atomic mass
- 132.91 u
- Category
- Alkali metal
- Group
- 1
- Period
- 6
- Block
- s-block
- State at room temp.
- Solid
- Electronegativity
- 0.79
- Melting point
- 301.59 K (28.4 °C)
- Boiling point
- 944 K (670.8 °C)
- Density
- 1.93 g/cm³
- Atomic radius
- 343 pm
- Ionization energy
- 3.894 eV
- Electron affinity
- 0.472 eV
- Radioactive
- No, has stable isotopes
- Discovered
- 1860
Cesium electron configuration
- Electron configuration
- [Xe] 6s1
- Full electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1
- Electron shells
- 2 · 8 · 18 · 18 · 8 · 1
The electron configuration of Cesium (Cs) is [Xe] 6s1. Its 55 electrons are arranged in shells as 2, 8, 18, 18, 8, 1.
Protons, neutrons and electrons in Cesium
A neutral Cesium atom has 55 protons and 55 electrons. Most Cesium atoms have about 78 neutrons: the atomic mass rounded to 133, minus the atomic number 55.
Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass
How many valence electrons does Cesium have?
1
Cesium has 1 valence electron in its outermost shell, shell 6. These are the electrons involved in chemical bonding.
Cesium orbital diagram
Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations
Molar mass of Cesium
132.91 g/mol
One mole of Cesium atoms (6.022 × 10²³ atoms) has a mass of 132.91 grams. Use this value to convert between grams and moles.
Cesium facts
- Cesium atomic clocks are used to define the length of one second.
- Cesium (Cs) has atomic number 55 and is a solid at room temperature. It was discovered in 1860.
Position in the periodic table
Cesium is element 55, in period 6 and group 1 of the periodic table, in the s-block.
Uses of Cesium
Cesium's largest use is in cesium formate, a dense salt solution used when drilling deep oil and gas wells. Because cesium gives up its outer electron so easily, it is used in photoelectric cells and some vacuum tubes. The radioactive isotope cesium-137 is used in industrial gauges that measure thickness or fluid levels and in some medical radiation equipment.
Who discovered Cesium?
Robert Bunsen and Gustav Kirchhoff discovered cesium in 1860 in Heidelberg, Germany, by spotting two bright blue lines in the spectrum of mineral water, making it the first element found with a spectroscope. Its name comes from the Latin caesius, meaning 'sky blue'.
Where does the name come from?
Cesium comes from the Latin caesius, meaning 'bluish gray' or 'sky blue'. Robert Bunsen and Gustav Kirchhoff discovered it in 1860 in mineral water and named it after the two bright blue lines in its spectrum.
Same group
Compare Cesium
FAQ
What is the electron configuration of Cesium?
The electron configuration of Cesium (Cs) is [Xe] 6s1. Its 55 electrons are arranged in shells as 2, 8, 18, 18, 8, 1.
How many protons, neutrons and electrons does Cesium have?
A neutral Cesium atom has 55 protons and 55 electrons. Most Cesium atoms have about 78 neutrons: the atomic mass rounded to 133, minus the atomic number 55.
How many valence electrons does Cesium have?
Cesium has 1 valence electron in its outermost shell, shell 6. These are the electrons involved in chemical bonding.
What is the molar mass of Cesium?
The molar mass of Cesium is 132.91 g/mol. This is the same number as its atomic mass, 132.91 u.
Is Cesium a metal?
Yes. Cesium is an alkali metal, so it is a metal.
Is Cesium radioactive?
Ordinary Cesium is not radioactive: it has at least one stable isotope. Like every element, it also has radioactive isotopes, most of them made in laboratories.
Where is Cesium on the periodic table?
Cesium is element 55, in period 6 and group 1 of the periodic table, in the s-block.