8.4: Atomic Properties And Chemical Reactivity - Chemistry LibreTexts

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Group 2: The Alkaline Earth Metals

Compared with the alkali metals, the alkaline earth metals are typically harder, more dense, melt at a higher temperature. The first ionization energies (\(I_1\)) of the alkaline earth metals are not as low as the alkali metals. The alkaline earth metals are therefore less reactive than the alkali metals (Be and Mg are the least reactive of the alkaline earth metals). Several physical properties of these elements are compared in Table \(\PageIndex{2}\).

Table \(\PageIndex{2}\): General Properties of Group 2 Metals
Element Electronic Configuration Melting Point (°C) Density (g/cm3) Atomic Radius Ionization Energy (kJ/mol)
Beryllium \([He]2s^2\) 1278 1.85 1.52 899
Magnesium \([Ne]3s^2\) 649 1.74 1.60 738
Calcium \([Ar]4s^2\) 839 1.54 1.97 590
Strontium \([Kr]5s^2\) 769 2.54 2.15 549
Barium \([Xe]6s^2\) 725 3.51 2.17 503

Calcium, and elements below it, react readily with water at room temperature:

\[Ca_{(s)} + 2H_2O_{(l)} \rightarrow Ca(OH)_{2(aq)} + H_{2(g)} \nonumber \]

The tendency of the alkaline earths to lose their two valence electrons is demonstrated in the reactivity of Mg towards chlorine gas and oxygen:

\[Mg_{(s)} + Cl_{2(g)} \rightarrow MgCl_{2(s)} \nonumber \]

\[2Mg_{(s)} + O_{2(g)} \rightarrow 2MgO_{(s)} \nonumber \]

The 2+ ions of the alkaline earth metals have a noble gas like electron configuration and are thus form colorless or white compounds (unless the anion is itself colored). Flame colors:

  • Calcium: brick red
  • Strontium: crimson red
  • Barium: green

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