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[note 2] Caesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at−116 °C (−177 °F). It is the least electronegative element having a stable isotope, caesium-133.
Rubidium is a chemical element; it has symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. [9] Rubidium is the first alkali metal in the group to have a density higher than water.
For example, rubidium has 5 electron shells, a property found in all other period 5 elements, whereas its electron configuration's ending is similar to all other alkali metals: s 1. [5] Rubidium also follows the trend of increasing reactivity as the atomic number increases in the alkali metals, for it is more reactive than potassium , but less ...
The stabilisation of ununennium's valence electron and thus the contraction of the 8s orbital cause its atomic radius to be lowered to 240 pm, [36]: 1729–1730 very close to that of rubidium (247 pm), [5] so that the chemistry of ununennium in the +1 oxidation state should be more similar to the chemistry of rubidium than to that of francium.
Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative stable element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite.
The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure. [ 2 ] Together with helium , these elements have in common an outer s orbital which is full [ 2 ] [ 3 ] [ 4 ] —that is, this orbital contains its full complement of two electrons, which the alkaline ...
Elements which contain at least one stable isotope. Slightly radioactive elements: the most stable isotope is very long-lived, with a half-life of over two million years. Radioactive elements: the most stable isotope has half-life between 800 and 34,000 years.
See also: Electronegativities of the elements (data page) There are no reliable sources for Pm, Eu and Yb other than the range of 1.1–1.2; see Pauling, Linus (1960).