Molecular formula of iron carbonyl
At. number of iron = 26 ; At. No. of the next noble gas, \(\mathrm{Kr}( i.e. EAN)=36\)
\(\therefore\) No. of electrons to be provided by \(\mathrm{CO}=36-26=10\)
Since each CO provides 2 electrons total number of carbonyl (CO) group \(=\frac{10}{2}=5\)
\(\therefore\) Molecular formula of simple iron carbonyl \(=\mathrm{Fe}(\mathrm{CO})_5\)
Molecular formula of chromium carbonyl
At. No. of chromium = 24 ; \(\mathrm{EAN}=36\)
\(\therefore\) No. of electron to be provided CO = 36 - 24 = 12
\(\therefore\) No. of CO group 12/2 = 6
Hence the molecular formula of chromium carbonyl will be \(\mathrm{Cr}(\mathrm{CO})_6\).
