The Alkaline Earth Metals form group 2 (2A) of the Periodic Table and include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). They are shiny, silvery metals, typically with an oxidation state of +2, and are studied for their reactivity, biological importance, and industrial applications.
Name origin and position in the Periodic Table
The term “alkaline earth” comes from their oxides, which were once called “earths” by alchemists and show strong basic (alkaline) properties. In the periodic table, they are located immediately to the right of the alkali metals (group 1) and before the d-block. Their valence configuration is ns².
Elements in the group
- Beryllium (Be) — Z=4
- Magnesium (Mg) — Z=12
- Calcium (Ca) — Z=20
- Strontium (Sr) — Z=38
- Barium (Ba) — Z=56
- Radium (Ra) — Z=88 (a radioactive element)
Electronic configuration and periodic trends
All alkaline earth metals have two valence electrons (ns²) and tend to lose them to form M²⁺ cations. Down the group:
- atomic radius increases, as does reactivity;
- ionization energy decreases and electropositivity increases;
- electronegativity increases from bottom to top, with Be being the most electronegative of the group.
Physical and chemical properties
- Physical state: all are solids at room temperature with metallic luster.
- Density and hardness: Be and Mg are light metals; others are denser. They are harder than alkali metals (Be is quite hard), but softer than many transition metals.
- Melting points: variable; Be and Mg have higher melting points than Ca, Sr, and Ba.
- Reactivity: they react with water and oxygen to form hydroxides and oxides, with reactivity increasing from Be → Ra.
Reactivity with water, oxygen, and halogens
- Water: Be does not react in liquid water; Mg reacts slowly in cold water but more rapidly in hot water/steam; Ca, Sr, and Ba react vigorously, releasing H₂ and forming hydroxides M(OH)₂ (strong bases).
- Oxygen: form oxides (MO) such as MgO and CaO. Some can also form peroxides/superoxides under special conditions.
- Halogens: readily form ionic halides (MX₂) such as CaCl₂ or MgBr₂. Most are soluble in water, except some fluorides, sulfates, and carbonates that are less soluble.
Important compounds and solubility
- Oxides: MgO (refractory), CaO (quicklime, strongly basic).
- Hydroxides: Mg(OH)₂ (antacid), Ca(OH)₂ (slaked lime, used in water treatment and construction).
- Carbonates: CaCO₃ (limestone, marble; cement; soil treatment). Carbonates become less soluble down the group.
- Sulfates: BaSO₄ is insoluble (used in radiological contrast); MgSO₄ and CaSO₄ are moderately soluble.
Occurrence and extraction
- Magnesium: extracted from brines and minerals (dolomite, magnesite) by electrolytic/thermal processes.
- Calcium: found in abundant compounds (limestone, gypsum) but never as free metal.
- Strontium: obtained from celestite (SrSO₄) and strontianite (SrCO₃).
- Barium: mainly from barite (BaSO₄) and witherite (BaCO₃).
- Beryllium: extracted from beryl (Be₃Al₂Si₆O₁₈) and chrysoberyl; controlled due to toxicity.
- Radium: found in trace amounts in uranium ores; radioactive, produced under strict handling protocols.
Applications
- Magnesium and alloys: lightweight, used in aerospace, automotive industries, pyrotechnics, and batteries.
- Calcium and compounds: essential in cement, lime, metallurgy (desulfurization), and agriculture.
- Strontium: salts color fireworks red; used in ferrites and ceramics.
- Barium: BaSO₄ in radiology (contrast agent), drilling fluids, ceramics; note that soluble Ba salts are toxic.
- Beryllium: beryllium–copper alloys (springs, contacts), X-ray windows (transparent to X-rays), aerospace components.
- Radium: historically used in luminous paints and medicine, now restricted due to radioactivity.
Biological aspects
- Magnesium: essential element in chlorophyll and enzymatic reactions; vital for life.
- Calcium: key role in bones and teeth, blood clotting, and cellular signaling.
Safety and environmental concerns
- Beryllium: toxic, can cause berylliosis; must be handled with protective equipment.
- Barium: soluble salts are poisonous; BaSO₄ is insoluble and safe for medical use.
- Radium: radioactive; requires shielding, containment, and special disposal methods.
- Reactive metals (especially Ca, Sr, Ba) must be stored under oil and kept away from moisture and ignition sources.
Curiosities (flame colors)
- Calcium: orange-red
- Strontium: bright red
- Barium: green
- Copper (reference): blue-green (not part of group 2, but used for comparison in flame tests)
FAQ – Frequently Asked Questions about Alkaline Earth Metals
Which are the Alkaline Earth Metals?
Beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
What is their typical oxidation state?
The most common oxidation state is +2 for all group members. Other states are rare.
How do they react with water?
Be does not react in liquid water; Mg reacts slowly in cold water but faster when heated; Ca, Sr, and Ba react increasingly vigorously, releasing H₂ and forming M(OH)₂.
Do they all have low density and softness?
No. Be is relatively hard and light; Mg is light and soft; Ca, Sr, and Ba are softer than most transition metals but denser than alkali metals.
Does radium have a “short life”?
Radium is radioactive. Its most common isotope, Ra-226, has a half-life of about 1600 years — short compared to stable elements, but long compared to many radioisotopes.
What are their main applications?
Mg in alloys and pyrotechnics; Ca in cement, lime, and agriculture; Sr in fireworks and ceramics; BaSO₄ as medical contrast; Be in aerospace and X-ray technology.