1.3.2 Typical properties of transition metals

Transition metals form ions with different charges

1. Unlike Group 1 metals, which only form $+1$ ions, transition metals can form ions with more than one charge.
2. The charges these metals can form are:
   1. Chromium: $+2,+3,+4,+5,+6$.
   2. Manganese: $+2,+3,+4,+5,+6,+7$.
   3. Iron: $+2,+3,+4,+5,+6$.
   4. Cobalt: $+2,+3,+4,+5$.
   5. Nickel: $+2,+3,+4$.
   6. Copper: $+1,+2,+3$.
3. The charge is shown by a Roman numeral, such as iron(II) ${Fe}^{2+}$ and iron(III) ${Fe}^{3+}$.

Different charges give differently coloured compounds

1. Transition metals form coloured compounds, while Group 1 compounds are usually white.
2. The colour depends on the metal ion and on its charge, so one metal can give several colours:
   1. Chromium: $+2$ blue, $+3$ green, $+6$ orange.
   2. Manganese: $+2$ pale pink, $+4$ brown-black, $+6$ green, $+7$ purple.
   3. Iron: $+2$ pale green, $+3$ reddish brown.
   4. Cobalt: $+2$ pink, $+3$ green.
   5. Nickel: $+2$ green.
   6. Copper: $+2$ blue.

Uses as catalysts

1. Many transition metals and their compounds are useful catalysts, which speed up reactions without being used up.
2. Manganese(IV) oxide catalyses the decomposition of hydrogen peroxide:
   1. $$2H_2{O}_2\to 2H_{2}O+O_2$$
3. Iron catalyses the Haber process, which makes ammonia:
   1. $$N_2+3H_2\rightleftharpoons 2{NH}_3$$
4. Nickel catalyses hydrogenation, used in the manufacture of margarine by adding hydrogen to the C=C double bonds in oils.