The neutron is slightly heavier than the proton.There are two reasons for the difference between mass number and isotopic mass, known as the mass defect: For example, 63Cu (29 protons and 34 neutrons) has a mass number of 63, and an isotopic mass in its nuclear ground state is 62.91367 u. The isotopic mass usually differs for other isotopes and is usually within 0.1 u of the mass number. One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.įor 12C, the atomic mass is exactly 12u since the atomic mass unit is defined from it. One atomic mass unit is equal to 1.66 x 10 -24 grams. The unit of measure for mass is the atomic mass unit (amu). Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance. See also: Properties of Caesium Atomic Mass of Caesium

Caesium has physical and chemical properties similar to those of rubidium and potassium.Ĭaesium – Properties Element Caesium Atomic Number 55 Symbol Cs Element Category Alkali Metal Phase at STP Solid Atomic Mass 132.9055 Density at STP 1.879 Electron Configuration 6s1 Possible Oxidation States +1 Electron Affinity 45.5 Electronegativity 0.79 1st Ionization Energy 3.8939 Year of Discovery 1860 Discoverer Kirchhoff, Gustav & Bunsen, Robert Thermal properties Melting Point 28.4 Boiling Point 669 Thermal Conductivity 36 Specific Heat 0.24 Heat of Fusion 2.092 Heat of Vaporization 67.74 The chemical symbol for Caesium is Cs.Ĭaesium is a soft, silvery-gold alkali metal with a melting point of 28.5 ☌, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium is a chemical element with atomic number 55 which means there are 55 protons and 55 electrons in the atomic structure.

Caesium element