Transition metals are special elements found in groups 3 to 12 of the periodic table. They have different chemical properties that set them apart from other groups, like alkali metals and halogens.

Here are some key features of transition metals:

1. Variable Oxidation States
   Transition metals can have more than one oxidation state, which means they can lose different numbers of electrons.
   For example:

   • Iron (Fe) can be found in a +2 state or a +3 state.
   • Manganese (Mn) can reach up to a +7 state.

2. Formation of Complex Ions
   These metals can make complex ions when they bond with other molecules called ligands.
   For instance, the complex ion $[Cu(NH_3)_4]^{2+}$ shows how copper can connect with ammonia, creating new properties.

3. Catalytic Activity
   Transition metals often help speed up chemical reactions. They are known as catalysts because they help reactions happen faster without getting used up.
   A good example is platinum (Pt), which is used in catalytic converters in cars to reduce harmful gases.

4. Color and Light Absorption
   Many compounds made from transition metals are colorful. This is because of the movement of electrons within the metal.
   For example:

   • Copper(II) sulfate is blue.
   • Potassium dichromate is orange.

On the other hand, alkali metals (in Group 1) react a lot and usually form +1 ions. Halogens (in Group 17) mostly exist as -1 ions.

These differences show how important transition metals are for many chemical reactions and industrial uses.