Physical & Chemical properties of Alkaline Earth Metal

Alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). They are all silver except for the gray beryllium. Their density is greater than the alkali metals, but is less than 4.5 g/cm³, and they are light metals. Their melting and boiling points are greater than those of the alkali metals. Density, melting point and boiling point do not change regularly with the increasing atomic number.

Alkaline earth metals have 2 electrons in their outermost electron shell, one more than alkali metals. They have a weaker tendency to lose electrons in chemical reactions than alkali metal atoms of the same period. Therefore, they are less active than alkali metals. However, there are still relatively few electrons in the outermost shell, making them more active than other metals. When alkaline earth metal atoms lose 2 electrons, they become doubly charged cation. They show a 2-valent state in all compounds.

Similar to alkali metals, the alkaline earth metals are more reductive with increasing atomic number. As the atomic number increases, the number of electron shells also increases, and the outermost electrons are more distant from the nucleus, weakening the attractive force. As a result, they are more likely to lose electrons in chemical reactions, and becomes more reductive.

Alkaline earth metals will burn when heated in air. At room temperature, they gradually oxidize and form oxides (with the general molecular formula RO). Alkaline earth metals can directly react with halogens to form stable compounds. They can also react with sulfur and nitrogen gases under heating conditions. Similar to alkali metals, they can replace hydrogen in acids and water. For example, calcium, strontium, and barium react vigorously with cold water, while magnesium reacts slowly due to the formation of a sparingly soluble hydroxide on the surface during the reaction, hindering the progress of reaction.

Alkaline earth metal oxides react with water to form hydroxides (with the general molecular formula R(OH)₂) and release a large amount of heat. Alkaline earth metal hydroxides are less soluble in water than alkali metal hydroxides. Their solubility in water increases gradually with increasing atomic number. Their aqueous solutions are clearly alkaline, but their alkalinity is much weaker than the alkali metal hydroxides.

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