Characteristics
Palladium belongs to group 10 in the periodic table:
| Z | Element | No. of electrons/shell |
|---|---|---|
| 28 | nickel | 2, 8, 16, 2 or 2, 8, 17, 1 |
| 46 | palladium | 2, 8, 18, 18 |
| 78 | platinum | 2, 8, 18, 32, 17, 1 |
| 110 | darmstadtium | unknown |
but has a very atypical configuration in its outermost electron shells compared to the other members of group 10 (see also niobium (41), ruthenium (44), and rhodium (45)), having fewer filled electron shells than the elements directly preceding it (a phenomenon unique to palladium).
Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and greatly increases its strength and hardness when it is cold-worked. Palladium dissolves slowly in sulfuric, nitric and hydrochloric acid. This metal also does not react with oxygen at normal temperatures (and thus does not tarnish in air). Palladium heated to 800°C will produce a layer of palladium(II) oxide (PdO). It lightly tarnishes in moist atmosphere containing sulfur.
Common oxidation states of palladium are 0, +1, +2 and +4. Although originally +3 was thought of as one of the fundamental oxidation states of palladium, there is no evidence for palladium occurring in the +3 oxidation state; this has been investigated via X-ray diffraction for a number of compounds, indicating a dimer of palladium(II) and palladium(IV) instead. In 2002, palladium(VI) was first reported.
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