Alkali metal

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The alkali metals are the elements from group 1 in the periodic table, consisting of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr).

Although hydrogen (H) is sometimes placed in the group 1, it is not considered an alkali metal.

Elements in the alkali metal groups

Lithium

Lithium, atomic number 3, is the lightest metal and has the highest melting point of the alkali metals. It burns with an extremely bright flame.

Sodium

Sodium, atomic number 11, is a reactive metal which burns with a powerful yellow flame.

Potassium

Potassium, atomic number 19, is even more reactive than sodium, and burns with a purple flame.

Rubidium

Rubidium, atomic number 37, is a very reactive metal, which is less often encountered, as it is expensive.

Caesium

Caesium (or cesium), atomic number 55, is the most reactive of the group, and has a slight gold coloration. It also has the lowest melting point of the group (28.5 °C).

Francium

Francium, atomic number 87, is radioactive and due to its very short half-life of its main isotope (22 minutes), cannot be isolated.

Properties

Chemical

All alkali metals readily react with air and violently with water. Potassium will form a dark layer of potassium peroxide, which is known to be shock sensitive.

Physical

Alkali metals are silvery-gray in color, except for caesium which has a pale gold coloration.

Safety

All alkali metals react violently with water. Potassium can form an explosive layer of peroxide in contact with air over months. Caesium and rubidium can be pyrophoric and react explosively with water, even in small amounts.

See also

References

Relevant Sciencemadness threads