55 - Cesium alkali metal
Discovered by Robert Bunsen in 1860
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.
H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
57-71 La-Lu Lanthanides
89-103 Ac-Lr Actinides
| Shell | Electrons | Orbitals |
|---|---|---|
| 1 | 2 | 2 in 1s |
| 2 | 8 | 2 in 2s + 6 in 2p |
| 3 | 18 | 2 in 3s + 6 in 3p + 10 in 3d |
| 4 | 18 | 2 in 4s + 6 in 4p + 10 in 4d |
| 5 | 8 | 2 in 5s + 6 in 5p |
| 6 | 1 | 1 in 6s |
silvery gold Appearance
133 u Atomic Mass
2.6 Å Atomic Radius
944 K Boiling Point
1 Group
1 Common Oxidation States
2.44 Å Covalent Radius
1.93 g/cm³ Density
45.5 kJ/mol Electron Affinity
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s1 Electron Configuration
[Xe] 6s1 Electron Configuration (semantic)
0.79 Electronegativity
55 Electrons
3.89 eV First Ionization Energy
1 ICSD Oxidation States
375.7, 2234.3, 3400 kJ/mol Ionization Energies
302 K Melting Point
8 Mendeleev Number
32.2 J/(mol·K) Molar Heat
6 Number of Shells
1 Electron Valency
78 Neutrons
55 Atomic Number
22 Number of Isotopes
1 Oxidation States
6 Period
Solid Phase
55 Protons
2, 8, 18, 18, 8, 1 Electron Shell Occupations
0.242 J/(g K) Specific Heat