Defining Alkaline Earth Metals
Alkaline earth metals are a group of six metallic chemical elements located in Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements are characterized by having two valence electrons in their outermost shell, which they readily lose during chemical reactions to form ions with a +2 charge.
Key Physical and Chemical Properties
These metals are typically shiny, silvery-white, and relatively soft, although they are harder than the alkali metals (Group 1). They exhibit low densities, low melting points, and low boiling points compared to most other metals. Chemically, they are highly reactive and electropositive, meaning they have a strong tendency to donate electrons and form ionic compounds, particularly with nonmetals like halogens and oxygen.
Common Examples and Applications
Magnesium is a vital component of chlorophyll in plants and essential for human bone health; it's also used in lightweight alloys for aircraft and in fireworks. Calcium is crucial for strong bones, teeth, and muscle function, widely found in dairy products and antacids. Strontium compounds are known for producing brilliant red colors in pyrotechnics, while barium compounds are used in medical diagnostic imaging as 'barium meals' to visualize the digestive tract.
Reactivity and Natural Occurrence
Due to their high reactivity, alkaline earth metals are never found as free, uncombined elements in nature. Instead, they are always present in compounds, typically as minerals within the Earth's crust. Their reactivity generally increases as you move down the group in the periodic table, with radium and barium being more reactive than beryllium and magnesium. They react vigorously with water, especially as you go down the group, producing hydrogen gas and metal hydroxides.