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55Cs132.905
Cesium
Alkali MetalCaesium 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.
Phase: SolidAppearance: silvery gold
2, 8, 18, 18, 8, 1
Physical Properties
Atomic Mass132.905451966 u
Density1.93 g/cm³
Melting Point301.7 K
Boiling Point944 K
Molar Heat32.21 J/(mol·K)
Period6
PhaseSolid
Chemical Properties
Electron Configuration1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s1
Semantic Config[Xe] 6s1
Shells2, 8, 18, 18, 8, 1
Electron Affinity45.505 kJ/mol
Electronegativity0.79
Ionization Energies
IE1: 375.7 kJ/molIE2: 2234.3 kJ/molIE3: 3400 kJ/mol
Discovery
Discovered byRobert Bunsen