Berzelius, Jöns JakobPronunciation: /bəːˈziːlɪəs/Definition of Berzelius, Jöns Jakob (1779–1848), Swedish analytical chemist. He determined the atomic weights of many elements and discovered cerium, selenium, and thorium. Berzelius, Jöns Jakob in other Oxford dictionaries Definition of Berzelius, Jöns Jakob in the US English dictionary