structural:reformatting
Chemical properties of the element

Like the other lanthanides, cerium metal is a good reducing agent, having standard reduction potential of E = −2.34 V for the Ce /Ce couple. It tarnishes in air, forming a passivating oxide layer like iron rust. A centimeter-sized sample of cerium metal corrodes completely in about a year. More dramatically, metallic cerium can be highly pyrophoric:

Being highly electropositive, cerium reacts with water. The reaction is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas: