List of misidentified chemical elements

Name	Symbol	Atomic number	Actual element	Discovery date	Discoverer
Anglohelvetium						See Helvetium
Ausonium	Ao	93	Neptunium	1934	Enrico Fermi	[1][2]
Austrium			Gallium	1886	Eduard Linnemann	Hypothesised from spectral line observations in the rare earth mineral orthite.[3] It was later confirmed that these lines were due to the recently discovered gallium.
Berzelium	Bz		Thorium	1901	Charles Baskerville
Bohemium		93	Neptunium	1934	Odolen Koblic
Carolinium	Cn		Thorium	1901	Charles Baskerville
Coronium			Iron	1869	Charles Augustus Young and William Harkness	Hypothesised from a at 530.3 nm emission line in the coronal spectrum; in the 1930s recognised as highly ionized iron, rather than a new element. Later, around 1902, renamed as Newtonium
Davyum			Iridium and rhodium	1877	Serge Kern
Decipium			Samarium and other rare earths	1878	Marc Delafontaine	Thought to have been isolated from the mineral samarskite in 1878.[4]
Dianium			Niobium and tantalum	1860	Wolfgang Franz von Kobell
Gnomium			Similarities to nickel and iron	1892	Gerhard Krüss and F. W. Schmidt	Not discovered, but hypothesised to explain discrepancies within the iron group elements for an early periodic table ordered by mass. The concept of atomic number clarified the situation without requiring the invention of a new element.
Helvetium		85	Astatine	1940	Walter Minder	Rediscovered [sic] in 1942 and named Anglohelvetium
Hesperium	Hs	94	Plutonium	1934	Enrico Fermi	[1][2]
Ilmenium			Niobium and tantalum	1847	R. Hermann
Lucium			Yttrium	1896	Prosper Barrière
Nebulium			Oxygen	1864	William Huggins
Newtonium						See Coronium
Pelopium			Niobium and tantalum	1846	Heinrich Rose
Sequanium		93	Neptunium	1939	Horia Hulubei	Thought to have been present in tantalite ore, actually not present, rather than mis-identified.[5]
Wasium			Mixture of rare earths	1862	J.F. Bahr

References

1. Element name etymologies
2. Fermi, Enrico (December 12, 1938). "Artificial radioactivity produced by neutron bombardment" (PDF). Nobel Lecture. pp. 416–417.
3. Linnemann, Eduard (1886). "Austrium, ein neues metallisches Element". Monatshefte für Chemie 7 (1): 121. doi:10.1007/BF01516564.
4. Delafontaine, Marc (1878). "Sur le décepium, métal nouveau de la samarskite". Journal de pharmacie et de chimie 28: 540.
5. Fontani, Marco (2005-09-10). "The Twilight of the Naturally-Occurring Elements: Moldavium (Ml), Sequanium (Sq) and Dor (Do)". International Conference on the History of Chemistry. Lisbon. pp. 1–8. Archived from the original on 2006-02-24.