6.2 Chemical Properties

Chemistry > s Block Elements > 6.0 Alkaline Earth Metals

  s Block Elements
    1.0 S-Block Elements
    2.0 Alkali Metals
    3.0 Anamolous Behaviour of Lithium
    4.0 Diagonal Relationship – similarities with magnesium
    5.0 Compounds of Sodium
    6.0 Alkaline Earth Metals
    7.0 Diagonal Relationship – Similarities with Aluminium:
    8.0 Anomalous Behaviour of Beryllium
    9.0 Compounds of Calcium
6.2 Chemical Properties
ReactionsComments
1. With water: $$M + 2{H_2}O \to M{(OH)_2} + {H_2}$$$Be$ probably reacts with steam, $Mg$ with hot water and $Ca$, $Sr$ and $Ba$ react rapidly with cold water.
2. With Acids: $$M + 2HCl \to MC{l_2} + {H_2}$$All the metals react with acids liberating $H_2$. With $HNO_3$, becomes passive due to formation of oxide layer.
3. With Nitrogen: $$3M + {N_2} \to {M_3}{N_2} + {H_2}$$All form nitrides at high temperature. Stability $$Be>Mg>Ca$$
4. With Halogens: $$M + {X_2} \to M{X_2}\left( {{X_2} = {F_2},C{l_2},B{r_2},{I_2}} \right)$$

All the metals form $MX_2$. No polyhalides are formed. Beryllium halides are covalent in nature due to small size and high charge of $Be^{2+}$ ions.


5. With Oxygen: $$2M + {O_2} \to 2MO$$$$Ba + {O_2} \to BaO\mathop \to \limits^{{O_2}hightemp.} Ba{O_2}$$
  • All metals form normal oxide.
  • $Ba$ forms peroxide ($BaO_2$)
6. With Hydrogen: $$\begin{equation} \begin{aligned} M + {H_2} \to M{H_2} \\ 2BeC{l_2} + LiAl{H_4} \to 2Be{H_2} + LiCl + AlC{l_3} \\\end{aligned} \end{equation} $$

Ionic Salt-like hydrides formed at high temperatures by $Ca$, $Sr$ and $Ba$.


Note: Beryllium Hydride ($BeH_2$) is difficult to prepare and less stable than others and can be prepared by the reaction of $BeCl_2$ and $LiAlH_4$.


7. With Carbon: $$\begin{equation} \begin{aligned} M + 2C \to M{C_2} \\ B{e_2}C + 4{H_2}O \to 2Be{(OH)_2} + C{H_4} \\ M{g_2}{C_3} + 4{H_2}O \to 2Mg{(OH)_2} + {C_3}{H_4} \\\end{aligned} \end{equation} $$
  • With exception of $Be$, other metals when heated with carbon in an electric furnace form carbides called Acetylides.
  • When $BeO$ is heated with carbon at ${2000^ \circ }C$ a brick red coloured carbide $Be_2C$ is formed. On hydrolysis it evolves methane and thus called methanide.
  • $MgC_2$ on heating changes to $Mg_2C_3$. On Hydrolysis evolves propyne.
8. With Sulphates: $$2MS{O_4} \to 2MO + 2S{O_2} + {O_2}$$Decompose on heating to give corresponding oxide.
9. With Nitrates: $$Be{(N{O_3})_2}\mathop \to \limits^\Delta [B{e_4}O\left( {N{O_3}{)_6}} \right] + {N_2}{O_5}$$On heating gives the mixture of $NO_2$ and $O_2$. Beryllium forms a basic nitrate in addition to the normal salt.
10. With Bases: $$Be + 2NaOH + 2{H_2}O \to N{a_2}Be{O_2}.2{H_2}O$$Reacts with $NaOH$ giving $H_2$ and sodium beryllate. ($Be$ is amphoteric as it reacts with acids as well as bases)


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