s Block Elements
4.0 Diagonal Relationship – similarities with magnesium
4.0 Diagonal Relationship – similarities with magnesium
The first element of group often shows resemblance to the second element of the neighbouring group on the right. The similarity between Li and Mg arises because of their similar ionic sizes.
| Nitrides | Li and Mg both form nitrides. Other alkali metals do not. $$\begin{equation} \begin{aligned} 6Li + {N_2}\mathop \to \limits^\Delta 2L{i_3}N \\ 3Mg + {N_2}\mathop \to \limits^\Delta M{g_3}{N_2}\\\end{aligned} \end{equation} $$ |
| Oxides | Both give their normal oxides, $Li_2O$, $MgO$, when they burn in Oxygen: peroxides and superoxides are not formed. Na forms Peroxide, $Na_2O_2$ while K forms superoxide, $KO_2$. |
| Carbonates and Bicarbonates | Like $MgCO_3$, $Li_2CO_3$ is decomposed by heat. Both carbonates are insoluble while $Na_2CO_3$ and $K_2CO_3$ are soluble. SOlid bicarbonates of lithium and magnesium do not exists. |
| Nitrates | $LiNO_3$ decomposes to give $Li_2O$ like $Mg{(N{O_3})_2}$, but other alkali metal nitrates give nitrite. |
| Chlorides | Both chlorides are hydrated, $LiCl.2H_2O$, $MgCL_2.6H_2O$, both are deliquescent and anhydrous salt in ether. |
| Fluorides | $LiF$ and $MgF_2$ are sparingly soluble in water. |
| Hydration | Both $Li^+$ and $Mg^2+$ are heavily hydrated. |
| Hydroxide | $LiOH$, $Mg{(OH)_2}$ both are weak bases and very slightly soluble in water, and their hydroxide decomposes on heating. |
| Perchlorates | Lithium perchlorate $(LiCl{O_4})$ and magnesium perchlorate $\left[ {Mg{{(Cl{O_4})}_2}} \right]$ both are extremely soluble in alcohol and used as water absorber. |
