Characteristics

Palladium belongs to group 10 in the periodic table:

Z	Element	No. of electrons/shell
28	nickel	2, 8, 16, 2
46	palladium	2, 8, 18, 18
78	platinum	2, 8, 18, 32, 17, 1
110	darmstadtium	2, 8, 18, 32, 32, 17, 1

but has a very atypical configuration in its outermost electron shells compared to the rest of the members of group 10, if not to all elements. (See also niobium (41), ruthenium (44), and rhodium (45).)

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.^[5] 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.

The metal has the uncommon ability to absorb up to 900 times its own volume of hydrogen at room temperatures. It is thought that this possibly forms palladium hydride (PdH₂) but it is not yet clear if this is a true chemical compound.^[5] When palladium has absorbed large amounts of hydrogen, it will expand slightly in size.^[12]

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. Recently, compounds with an oxidation state of +6 were synthesised.