55 2 · 8 · 18 · 18 · 8 · 1

Caesium, Cs, element 55

Alkali metal· Period 6· Group 1· s-block

Configuration [Xe]6s¹

Atomic weight: 132.905Da
Phase: solid
Density: 1.873g/cm³
Melting point: 301.65K 28.5 °C
Boiling point: 944.15K 671 °C
Electronegativity: 0.79

Soft silvery-white metallic element belonging to group 1 of the periodic table. One of the three metals which are liquid at room temperature. Cs-133 is the natural, and only stable, isotope. Fifteen other radioisotopes exist. Caesium reacts explosively with cold water, and ice at temperatures above 157K. Caesium hydroxide is the strongest base known. Caesium is the most electropositive, most alkaline and has the least ionization potential of all the elements. Known uses include the basis of atomic clocks, catalyst for the hydrogenation of some organic compounds, and in photoelectric cells. Caesium was discovered by Gustav Kirchoff and Robert Bunsen in Germany in 1860 spectroscopically. Its identification was based upon the bright blue lines in its spectrum. The name comes from the latin word caesius, which means sky blue. Caesium should be considered highly toxic. Some of the radioisotopes are even more toxic. Description from mendeleev.

Back to the table

The outermost shell: the valence electronsThe inner shellsThe nucleus One bead for each electron, on the ring of its shell, counted from the nucleus out. The rings turn at their own pace; the model is Bohr's picture of the atom, which places electrons in shells but not on true orbits.

Atomic properties

5 of 5 fields have a value for caesium

Atomic weight The standard atomic weight. For an element with no stable isotope, the mass of its longest-lived isotope.: 132.9055Da; Source: mendeleev
Electron configuration: [Xe]6s¹; Source: mendeleev
Uncertainty of the atomic weight: 6×10⁻⁸Da; Source: mendeleev
Electron configuration in full The electron configuration with the noble-gas core written out.: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶6s¹; Source: Worked outfrom electron configuration
Electrons in each shell Counted from the electron configuration, from the first shell outward.: 2 · 8 · 18 · 18 · 8 · 1; Source: Worked outfrom electron configuration

Screening of each subshell

Clementi's screening constants: how much of the nucleus's charge the other electrons hide from an electron in each subshell. What is left is the effective nuclear charge it feels.

Subshell	Screening σ	Effective charge Z − σ
1s	1.0957	53.9043
2s	14.4884	40.5116
2p	4.1804	50.8196
3s	18.6226	36.3774
3p	18.4222	36.5778
3d	14.0194	40.9806
4s	27.9576	27.0424
4p	29.1424	25.8576
4d	32.1616	22.8384
5s	39.5555	15.4445
5p	41.349	13.651
6s	48.637	6.363