Elements in the periodic table are arranged by increasing atomic weight, with each element provided with a chemical symbol used in place of the element’s full name. The periodic table is further arranged into rows and columns known as periods and groups. Periods and groups are characterized by similarities in physical and chemical properties.
Alkaline Earth Metals are a group of chemical elements in the periodic table, found in the second group (Group 2 or IIA). The name “alkaline” comes from the fact that compounds of these elements form basic (pH greater than 7) or alkaline solutions when dissolved in water.
In other words alkaline earth metals definition is derived from early scientific studies of these elements. For instance, the term ”alkaline” is derived from the basic (as opposed to acidic) nature of the compounds formed by these elements when bonded with oxygen. In many cases alkaline earth metals form oxides when combining with oxygen. Metal oxides, the type formed by alkaline metals, occur when metals bond with oxygen. The term ”earth” refers to the observation that metals from group 2, such as magnesium and calcium, also represent common components of the earth’s crust.
General Properties
- Group Members: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).
- Position: They are positioned in the s-block of the periodic table.
- Valence Electrons: Each has two electrons in their outermost shell, which explains their similar chemical behavior.
Physical Properties
- Appearance: Typically silver-white and shiny, though beryllium tends to be grayish.
- Density: Increases down the group. For example, beryllium has the lowest density, while barium and radium are denser.
- Melting and Boiling Points: Generally, melting and boiling points decrease from beryllium to radium, though magnesium is an exception with a higher melting point than calcium due to its smaller atomic size and stronger metallic bonding.
Chemical Properties
- Reactivity: They are less reactive than alkali metals (Group 1) but still quite reactive with water, especially as you move down the group.
- Reaction with Water: The reactivity with water increases down the group. Beryllium hardly reacts with water, while calcium, strontium, barium, and radium react vigorously, forming hydroxides and hydrogen gas.
- Compounds: They form oxides, hydroxides, and salts. Their oxides are basic and react with water to form hydroxides.
- Flame Tests: Compounds of these metals often impart characteristic colors to flames:
- Beryllium – No distinct color.
- Magnesium – Bright white (often used in flares).
- Calcium – Brick red.
- Strontium – Crimson red.
- Barium – Green or apple green.
- Radium – Due to its radioactivity, it’s not commonly used in flame tests but would theoretically give a red color.
Occurrence and Extraction
- Natural Occurrence: They are found in various minerals, often in combination with other elements. For instance, magnesium is abundant in seawater, while calcium is a major component of limestone (calcium carbonate).
- Extraction:
- Magnesium: Often extracted from magnesium chloride or sulfate through electrolysis.
- Calcium: Produced by the electrolysis of molten calcium chloride.
- Strontium and Barium: Obtained from their respective minerals by reduction with carbon or by electrolysis.
- Radium: Extracted from uranium ores in minute quantities due to its rarity and radioactivity.
Uses
- Beryllium: Used in alloys (with copper or nickel) for applications requiring lightness, strength, and resistance to heat, like aerospace components.
- Magnesium: Widely used in lightweight alloys, fireworks, and as a sacrificial anode in cathodic protection.
- Calcium: Essential in bone structure in animals, in the form of calcium phosphate. Also used in steel production, and as lime in agriculture.
- Strontium: Compounds are used in fireworks (for red color), in glass for color TV tubes (to block X-rays), and as a source of beta particles in radiotherapy.
- Barium: Barium sulfate is used in oil drilling and medical imaging (barium meals). Barium carbonate is used in rat poison.
- Radium: Historically significant in the study of radioactivity, though its use has declined due to health risks. Its salts were used to make luminous paints.
Environmental and Health Impact
- Calcium: Vital for biological systems but excessive intake can lead to health issues like kidney stones.
- Magnesium: Essential for life; deficiency or excess can lead to health problems.
- Radium: Highly radioactive, exposure can cause cancer and other severe health issues.
Compounds of Alkaline Earth Metals
Beryllium (Be) Compounds
- Beryllium Oxide (BeO) – Used in electronics and refractories due to its high thermal conductivity.
- Beryllium Chloride (BeCl₂) – Lewis acid, used in organic synthesis.
- Beryllium Sulfate (BeSO₄) – Used in analytical chemistry and as a catalyst.
Magnesium (Mg) Compounds
- Magnesium Oxide (MgO) – Known as magnesia, used in refractory materials and as an antacid.
- Magnesium Hydroxide (Mg(OH)₂) – Milk of magnesia, used as an antacid and laxative.
- Magnesium Chloride (MgCl₂) – Used in road de-icing, dust control, and as a source of magnesium for metallurgical processes.
- Magnesium Sulfate (MgSO₄) – Epsom salts, used in bath salts, agriculture, and medicine.
- Magnesium Carbonate (MgCO₃) – Used in cosmetics, as a drying agent, and in fire-extinguishing powders.
Calcium (Ca) Compounds
- Calcium Oxide (CaO) – Quicklime, used in cement production, steel making, and wastewater treatment.
- Calcium Hydroxide (Ca(OH)₂) – Slaked lime, used in mortar, plaster, and for water treatment.
- Calcium Chloride (CaCl₂) – Used for de-icing, dust control, and in refrigeration brines.
- Calcium Sulfate (CaSO₄) – Gypsum, used in plaster, drywall, and as a building material.
- Calcium Carbonate (CaCO₃) – Limestone, chalk, and marble; used in construction, agriculture (lime), and as a filler in paper, paint, and plastics.
Strontium (Sr) Compounds
- Strontium Oxide (SrO) – Used in glass for color TV tubes and in refining sugar.
- Strontium Chloride (SrCl₂) – Used in toothpaste for sensitive teeth and in fireworks for red color.
- Strontium Sulfate (SrSO₄) – Used in paints, pigments, and in drilling fluids.
- Strontium Carbonate (SrCO₃) – Used in the manufacture of glass for color TV tubes and in fireworks.
Barium (Ba) Compounds
- Barium Oxide (BaO) – Used in the manufacture of lubricating oils and in glassmaking.
- Barium Hydroxide (Ba(OH)₂) – Used as a base in chemical analysis and in the production of lubricants.
- Barium Chloride (BaCl₂) – Used in the manufacture of heat treatment salts, in barium-containing chemicals, and in fireworks.
- Barium Sulfate (BaSO₄) – Barytes or heavy spar, used in medical imaging (barium meals), as a filler or extender in paints, plastics, and rubber.
- Barium Carbonate (BaCO₃) – Used in the manufacture of electronic components, in rat poison, and to purify chemicals.
Radium (Ra) Compounds
- Radium Chloride (RaCl₂) – Used historically in radiotherapy and for luminous paints, though its use has declined due to radioactivity risks.
- Radium Bromide (RaBr₂) – Also used historically in luminous paints and in the study of radioactivity.