Alkali and alkaline earth metals are a group of metals in the modern periodic table which forms part of the S-block elements. Beryllium, magnesium, calcium, strontium, barium, and radium are alkali earth metals. These metals are so called because the oxides and hydroxides formed by these metals are alkaline in nature and are the mostly found in the earth’s crust. Lithium, sodium, potassium, rubidium, and francium are alkali metals. These metals are called alkali metals due to the formation of hydroxides which are highly alkaline in nature when they react with water.
The occurrence of alkali earth metals:
Beryllium is a rare element found in the earth’s crust at a concentration of two to six parts per million in which most of it is found in the soil layer. Small traces of this element are found in seawater and in freshwater, its concentration is found to be 0.1 parts per billion. The most common alkaline earth metals found in the earth’s crust are magnesium and calcium. Magnesium is the eighth most abundant element and calcium is the fifth most abundant element. Magnesium and calcium are the only two alkaline metals which are found in an elemental state in nature.
Carnalite, dolomite, and magnesite are rocks which are made up of magnesium and chalk, limestone, anhydrite, and gypsum are rocks which are made up of calcium. Barium is mostly found in barite mineral. The occurrence of barium is rare in the earth’s crust. Strontium is found in the earth crust and it is the fifteen most abundant elements in it. Radium is mainly found in uranium bearing ores as it is a decay product of uranium.
The occurrence of alkali metals:
Alkali metals are silvery white soft metals which are not found in their free state in nature. In the order of abundance, the position of lithium is 35. It mainly exists as a silicate such as lepidolite. Sodium is mostly found in nature in its combined state. It is usually found in salt water lakes and oceans. Potassium is available abundantly in nature and it occupies the eighth position in the order of abundance in the earth’s crust. Potassium is found in plant and animals tissues.
An important fraction of the soil is made up of potassium. It is found in various minerals such as carnallite (KAlSi3O8), sylvite (KCl) to name a few. Sodium along with potassium makes up 4% of the earth’s crust. Rubidium takes up the 16th position in the order of abundant elements in the earth’s crust. It is mostly distributed and large deposits of this metal are usually not found. Cesium is found in crystal rocks and francium is found only in radioactive form.
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