chemistry-class-12-unit-09-chapter-02-coordination-compounds-l-2-5-vwvzravtpg8

### <Success>Coordination compounds - II</Success>
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<thead>
<tr>
<th>Colour</th>
<th>Formula</th>
<th>Solution conductivity corresponds to</th>
</tr>
</thead>
<tbody>
<tr>
<td>Yellow</td>
<td>$[Co(NH_3)_6]^{3+}3Cl^-$</td>
<td>1:3 electrolyte</td>
</tr>
<tr>
<td>Purple</td>
<td>$[CoCl_2(NH_3)_5]^{2+}2Cl^-$</td>
<td>1:2 electrolyte</td>
</tr>
<tr>
<td>Green</td>
<td>$[CoCl_2(NH_3)_4]^1Cl^-$</td>
<td>1:1 electrolyte</td>
</tr>
<tr>
<td>Violet</td>
<td>$[CoCl_2(NH_3)_4]^1Cl^-$</td>
<td>1:1 electrolyte</td>
</tr>
</tbody>
</table>
<ul>
<li>Molar conductivity $(\lambda_M)$ of a solution at a given concentration is the conductance of the solution containing one mole of electrolyte kept between two electrodes with area of cross section (A) and at a distance of unit length</li>
</ul>
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### <Success>Coordination compounds - II</Success>
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<h4 id="important-points">Important points</h4>
<ul>
<li>In $[Co(NH_3)_6]Cl_3$ the ammonia molecules and the cobalt atom form a complex ion; the chloride ions are not part of the complex but are held to it by ionic forces</li>
<li>May also be main group metal ions</li>
<li>Werner postulated that most elements exhibit two types of valence: primary valence and secondary valence</li>
<li>In modern terminology, primary valence corresponds to the oxidation number and secondary valence to the coordination number of the element</li>
<li>In $CoCl_3.6NH_3$, according to Werner, cobalt has a primary valence of 3 and a secondary valence of 6</li>
</ul>
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### <Success>important terms</Success>
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<ul>
<li><strong>Coordination entity</strong>: It constitutes a central metal atom or ion bonded to a fixed number of ions or molecules</li>
<li><strong>Central atom/ion</strong>: It is the atom/ion to which a fixed number of ions/groups are bound in a definite geometrical arrangement</li>
<li><strong>Coordination number</strong>: It is the number of ligand donor atoms to which the metal is directly bonded</li>
<li>In the complex ions, $[PtCl_6]^{2-}$ and $[Ni(NH_3)_4]^{2+}$, the coordination number of Pt(II) and Ni(II) are 6 and 4 respectively</li>
<li>The term ligand (Latin: ligare, to bind) was first used by Alfred Stock in 1916 in relation to silicon chemistry</li>
</ul>
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### <Success>important terms</Success>
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<ul>
<li>
<p><strong>Ligands:</strong> The ions or molecules bound to the central atom/ion in the coordination entity are called ligands</p>
</li>
<li>
<p>Can be imple ions like $Cl^-$, small molecules like $H_2O$ or $NH_3$, larger molecules $H_2NCH_2CH_2NH_2$ or $N(CH_2CH_2NH_2)_3$ or even macromolecules, such as proteins</p>
</li>
<li>
<p>Depending on the number of donor atoms present, ligands are classified as monodentate, bidentate, or polydentate</p>
</li>
</ul>
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### <Success>important terms</Success>
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<h4 id="bidenate-ligand">Bidenate ligand</h4>
<ul>
<li>Ethylenediamine</li>
<li>Oxalate ion</li>
</ul>
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### <Success>Chelation</Success>
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<h4 id="important-points-1">Important points</h4>
<ul>
<li>CN 4: The tetrahedron is the more common while the square planar is found almost exclusively with metal ions having a $d^8$ electronic configuration</li>
<li><strong>Tetrahedral:</strong> There are large numbers of tetrahedral cobalt(II) complexes known</li>
<li>Tetrakis(triphenylphosphine)palladium</li>
</ul>
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