Alkaline Earth Metals Flashcards

A set of vocabulary flashcards covering alkaline earth metals, including their occurrence, electronic configurations, physical and chemical trends, key compounds, minerals, reactions, cement chemistry, and biological importance.

Abundance Order of Alkaline Earth Metals

The order of abundance (% by weight) in the Earth's crust is $Ca > Mg > Ba > Sr > Be$, with $Ca$ and $Mg$ being the $5\text{th}$ and $6\text{th}$ most abundant elements.

Magnesite

An important mineral of magnesium with the chemical formula $MgCO_3$.

Dolomite

An important mineral containing both calcium and magnesium with the chemical formula $MgCO_3 \cdot CaCO_3$ (or $CaCO_3 \cdot MgCO_3$).

Carnallite

A hydrated double salt mineral of potassium and magnesium with the chemical formula $KCl \cdot MgCl_2 \cdot 6H_2O$.

Kieserite

A hydrated magnesium sulphate mineral with the chemical formula $MgSO_4 \cdot H_2O$.

Gypsum

A calcium sulphate dihydrate mineral with the chemical formula $CaSO_4 \cdot 2H_2O$.

Fluorspar

A calcium mineral with the chemical formula $CaF_2$.

Fluorapatite

A mineral of calcium containing phosphate and fluoride with the formula $CaF_2 \cdot 3Ca_3(PO_4)_2$ (or $3Ca_3(PO_4)_2 \cdot CaF_2$).

Anhydrite

Anhydrous calcium sulphate with the chemical formula $CaSO_4$.

Radium Isotope ($^{226}_{88}Ra$)

A radioactive alkaline earth metal whose longest-lived isotope is $^{226}_{88}Ra$ with a half-life of $t_{1/2} = 1600\,\text{yr}$.

Hydration Enthalpy Order of Group IIA Cations

Decreases with an increase in ionic size down the group: $Be^{2+} > Mg^{2+} > Ca^{2+} > Sr^{2+} > Ba^{2+}$.

Heats of Hydrated Group IIA Cations ($-\Delta H$ in $kJ\,mol^{-1}$)

The specific heats of hydration are $Be^{2+} = 2406$, $Mg^{2+} = 1929$, $Ca^{2+} = 1632$, $Sr^{2+} = 1485$, and $Ba^{2+} = 1276$.

Flame Test Colors of Group IIA Elements

$Ca$ gives Brick red, $Sr$ gives Crimson red, $Ba$ gives Apple green, and $Ra$ gives Carmine. $Be$ and $Mg$ do not show flame colors due to high excitation energy.

Density Trend of Alkaline Earth Metals

Decreases slightly from $Be$ to $Ca$ due to solid lattice packing and increases from $Ca$ to $Ba$ due to vacant 3d-orbitals in $Ca$; the order is $Ca < Mg < Be < Sr < Ba$.

Standard Reduction Potentials ($E^\circ_{SRP}$) of Group IIA Metals

Values are $Be^{2+}/Be = -1.85\,\text{V}$, $Mg^{2+}/Mg = -2.37\,\text{V}$, $Ca^{2+}/Ca = -2.87\,\text{V}$, $Sr^{2+}/Sr = -2.89\,\text{V}$, and $Ba^{2+}/Ba = -2.91\,\text{V}$.

Hydrolith

Calcium hydride ($CaH_2$), an ionic saline hydride that reacts with water to liberate hydrogen gas.

Maximum Covalency of Beryllium

Beryllium has a maximum coordination number and covalency of $4$ due to the non-availability of vacant d-orbitals.

Ammoniated Electrons in Liquid Ammonia

Alkaline earth metals dissolve in liquid ammonia to form colored solutions containing ammoniated electrons; evaporating these solutions yields hexammoniates $[M(NH_3)_6]$.

Amphoteric Behavior of Beryllium Oxide and Hydroxide

$BeO$ and $Be(OH)_2$ react with both acids and alkalis, forming beryllate ions $[Be(OH)_4]^{2-}$ in alkali.

Beryllium Chloride ($BeCl_2$) Vapour and Solid Phase Structures

Exists as an $sp^3$ hybridized tetrahedral polymer in the solid phase, an $sp^2$ hybridized planar dimer in the vapour phase, and dissociates into a linear monomer ($Cl-Be-Cl$) at high temperatures.

Diagonal Relationship of Beryllium with Aluminium

Both metals show similar polarizing power ($\text{charge}/\text{radius}^2$), form protective oxide films resistant to acids, dissolve in excess alkali to form $[Be(OH)_4]^{2-}$ and $[Al(OH)_4]^{-}$, and form chlorine-bridged dimeric chlorides soluble in organic solvents.

Sorel's Cement (Magnesia Cement)

A hard-setting cement prepared by mixing a saturated solution of magnesium chloride with magnesium oxide ($MgO$), having the composition $MgCl_2 \cdot 5MgO \cdot xH_2O$.

Magnesia Alva

A basic magnesium carbonate precipitate with the chemical formula $3MgCO_3 \cdot Mg(OH)_2 \cdot 2H_2O$, formed when sodium carbonate is added to a solution of a magnesium salt.

Nitrolim

A fertilizer mixture of calcium cyanamide ($CaCN_2$) and graphite ($C$), prepared by reacting calcium carbide with nitrogen gas ($CaC_2 + N_2 \rightarrow CaCN_2 + C$).

Melamine Structure and Synthesis

A heterocyclic organic compound with formula $C_3H_6N_6$ synthesized from cyanamide ($H_2NCN$) that is used in the manufacture of hard plastics.

Calcite

The most stable, colourless, rhombohedral form of calcium carbonate ($CaCO_3$) where each $Ca^{2+}$ ion is coordinated by $6$ oxygen atoms of carbonate ions.

Aragonite

A less stable, red-brown or yellow, orthorhombic form of calcium carbonate ($CaCO_3$) where each $Ca^{2+}$ ion is coordinated by $9$ oxygen atoms of carbonate ions.

Plaster of Paris

Calcium sulphate hemihydrate ($CaSO_4 \cdot \frac{1}{2}H_2O$ or $2CaSO_4 \cdot H_2O$) prepared by heating gypsum at $120-130\,^\circ\text{C}$.

Dead Burnt Plaster

Anhydrous calcium sulphate ($CaSO_4$) formed when Plaster of Paris is heated strongly above setting temperatures, losing all water of crystallization.

Composition of Portland Cement

Contains $CaO$ ($60\%$), $SiO_2$ ($20\%$), $Al_2O_3$ ($5\%$), $MgO$ ($2\%-3\%$), $Fe_2O_3$ ($2\%$), and $SO_3$ ($1.5\%-2.5\%$), with main active constituents being Tricalcium silicate ($51\%$), Dicalcium silicate ($26\%$), and Tricalcium aluminate ($11\%$).

Role of Gypsum in Cement

Gypsum ($CaSO_4 \cdot 2H_2O$) is added ($2\%-3\%$ by weight) to cement clinker to retard and slow down the rate of setting of cement.

Biological Abundance of Magnesium and Calcium in Humans

An adult human body contains about $25\,\text{g}$ of $Mg$ and $1200\,\text{g}$ of $Ca$; daily requirement of $Ca$ is $200-300\,\text{mg}$, and blood plasma $Ca^{2+}$ concentration is about $100\,\text{mg/L}$.