Fill in the electronic structures for: a cobalt atom, $1s^22s^22p^6\ \ldots$ ; cobalt in the $+3$ oxidation state, $1s^22s^22p^6\ \ldots$
When cobalt(II) sulfate is dissolved in water, cobalt forms complex ions. What does the term complex ion mean?
State two chemical properties of cobalt, apart from forming complexes, that a typical s-block element does not show.
Cobalt(II) ions, $\text{Co}^{2+}(aq)$, have some chemical properties like those of copper(II) ions, $\text{Cu}^{2+}(aq)$. Use this clue and the Data Booklet to suggest the formula of the cobalt species formed in each of the following reactions. State the type of reaction occurring in each case: $\text{Co}^{2+}(aq)$ + an excess of $\text{NH}_3(aq)$; $\text{Co}^{2+}(aq) + \text{OH}^-(aq)$; $\text{Co}^{2+}(aq) + \text{S}_2\text{O}_8^{2-}(aq)$.
Some transition elements are found in superconductors. These are substances that carry electric current with little or no resistance. Compound Q is a superconductor and contains 13.4% yttrium, 41.2% barium, 28.6% copper and 16.8% oxygen by mass. Show that the empirical formula of Q is $\text{YBa}_2\text{Cu}_3\text{O}_7$. Show all your working.
The table gives the oxidation numbers of yttrium, barium and oxygen in Q. Calculate the average oxidation number of copper in Q.
Hence deduce the oxidation number for each of the three copper atoms in Q.