Cesium

Alkali metal · atomic number 55

55132.905451966CsCesiumSolidAlkali metal

Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (82 °F), which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium.

Properties of Cesium

Element category	Alkali metal
Atomic number	55
Atomic mass	132.905451966 u
Phase at STP	Solid
Group	1
Period	6
Block	s
Electron configuration	[Xe] 6s1
Electrons per shell	2, 8, 18, 18, 8, 1
Electronegativity (Pauling)	0.79
Melting point	301.7 K (29 °C)
Boiling point	944 K (671 °C)
Density	1.93 g/cm3
Discovered by	Robert Bunsen

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About the alkali metal group

Soft, wildly reactive metals of group 1 — they fizz in water and never occur pure in nature. Lithium, sodium, potassium and friends.

Data: Periodic-Table-JSON (CC BY-SA 3.0) · stored statically on our server. https://en.wikipedia.org/wiki/Cesium

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🧪 Reactive nonmetal

11 elements: Elements that readily gain or share electrons — the building blocks of water, air, living tissue and most organic chemistry.

🧪 Noble gas

6 elements: Full outer electron shells make these gases almost inert: they barely react, glow in discharge lamps and are used to create unreactive atmospheres.

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6 elements: Soft, wildly reactive metals of group 1 — they fizz in water and never occur pure in nature. Lithium, sodium, potassium and friends.

🧪 Alkaline earth metal

6 elements: Reactive group-2 metals a step calmer than the alkalis: magnesium, calcium and the structural and biological workhorses among them.

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