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Normal metals like sodium or Calcium have a positive charge as $\ce{Na}^+$ or $\ce{Ca}^{2+}$. Transition metals have a loot of variable oxidation states.

Yesterday I read about Iridium in Wikipedia and it stated that

a +9 oxidation state has been found in $\ce{IrO_4^+}$

which is astounding for me...

So i was thinking can metals have a net negative charged ion also?

According to Google :

Ions: An atom or group of atoms gain an electric charge by gaining or losing an electron, usually through bonding. Cation: An atom loses electrons and is positive ex: $\ce{Ca^2^+}$. Anion: An atom gains electrons and is negative ex: $\ce{Cl-}$. Metals usually form cations while nonmetals usially form anions. [source: chemwiki UCDavis]

Since it is written that metals USUALLY have positive charges which means there may be conditions or compounds when they have negative charges too. Is it possible?

Also can noble gases form ions too?

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    $\begingroup$ Addressing your noble gas ion question, they have been known for over 50 years to make compounds with formal positive charges on the noble gas atoms, though discrete noble gas cations (i.e. $\ce{Ng^{x+}}$) are not known in compounds. $\endgroup$
    – Nicolau Saker Neto
    Commented Mar 16, 2015 at 14:46
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    $\begingroup$ More interestingly, regarding the possibility of noble gas anions, all noble gases up to radon have an endothermic electron affinity, and could not even in principle stabilize a negative charge on them. However, due to relativistic effects, the superheavy noble gas ununoctium may be able to form an isolated $\ce{Uuo^-}$ anion, though it would presumably be quite reactive. Whether a compound can be made with a $\ce{Uuo^-}$ anion is not known. $\endgroup$
    – Nicolau Saker Neto
    Commented Mar 16, 2015 at 14:49
  • $\begingroup$ related: chemistry.stackexchange.com/questions/6923/…, chemistry.stackexchange.com/questions/26527/… $\endgroup$
    – Mithoron
    Commented Mar 18, 2015 at 11:50
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    $\begingroup$ @Nocolau there is no longer "ununoctium". It's now oganesson, Og. $\endgroup$
    – Oscar Lanzi
    Commented Jan 21, 2018 at 11:16
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    $\begingroup$ Search “Alkalide” for information on things like $\ce{Na-}$ and other first column negative states $\endgroup$
    – H. Khan
    Commented Jun 18, 2018 at 21:06

1 Answer 1

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These species usually do not exist in nature, but they can be synthesized.

  1. Silver has been reduced in liquid ammonia to give $\ce{Ag-}$.
  2. A lot of anionic metal carbonyl complexes $\ce{M(CO)_{n}^{m-}}$ have been synthesized:

-1

  • $\ce{[V(CO)6]-}$, $\ce{[Nb(CO)6]-}$, $\ce{[Ta(CO)6]-}$, $\ce{[Mn(CO)5]-}$, $\ce{[Ir(CO)4]-}$, $\ce{[Co(CO)4]-}$, $\ce{[Rh(CO)4]-}$

-2

  • $\ce{[Ti(CO)6]^{2-}}$, $\ce{[Zr(CO)6]^{2-}}$, $\ce{[Hf(CO)6]^{2-}}$, $\ce{[Fe(CO)4]^{2-}}$, $\ce{[Ru(CO)4]^{2-}}$, $\ce{[Os(CO)4]^{2-}}$

-3

  • $\ce{[V(CO)5]^{3-}}$, $\ce{[Nb(CO)5]^{3-}}$, $\ce{[Ta(CO)5]^{3-}}$, $\ce{[Mn(CO)4]^{3-}}$, $\ce{[Re(CO)4]^{3-}}$

-4

  • $\ce{[Cr(CO)4]^{4-}}$, $\ce{[Mo(CO)4]^{4-}}$

There's a review by John E. Ellis: Highly Reduced Metal Carbonyl Anions: Synthesis, Characteri's zation, and Chemical Properties on these compounds.

Edit

While Christian Aichinger's comment concerning $\pi$-backbonding in metal carbonyls is correct, it is important to realize that $\ce{CO}$ is a neutral ligand!

With other words: The Mond process: $\ce{Ni(s) + 4CO -> Ni(CO)4}$, using nickel powder and carbon monoxide, is not a redox reaction and the oxidation state of the metal still is $0$ in the metal carbonyl.

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    $\begingroup$ The metal carbonyls have pretty much the same old positive oxidation state if we remove those carbonyls... But the Ag- is good .... $\endgroup$
    – NeilRoy
    Commented Mar 16, 2015 at 10:43
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    $\begingroup$ Another noteworthy example would be CsAu which contains gold in the -1 oxidation state. $\endgroup$
    – J. LS
    Commented Mar 16, 2015 at 11:53
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    $\begingroup$ I don't fully agree with @NeilRoy, but even though CO is neutral, it can pull electron density away from the metal via π backbonding ($ \ce{ M^{-}-C=O <-> M=C-O^{-} } $). I think it's helpful to remember that oxidation states are a helpful formalism to keep track of electrons, but they don't always describe the real electron distribution very well. $\endgroup$
    – Christian Aichinger
    Commented Mar 16, 2015 at 12:40
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    $\begingroup$ Very interesting examples of metal anions are the alkalides $\ce{Na^-}$, $\ce{K^-}$, $\ce{Rb^-}$, and $\ce{Cs^-}$. Yes that's right, monoanions of the familiar alkali metals! Who said old dogs can't learn new tricks? $\endgroup$
    – Nicolau Saker Neto
    Commented Mar 16, 2015 at 14:34
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    $\begingroup$ @NicolauSakerNeto Change your comment into an answer $\endgroup$
    – NeilRoy
    Commented Mar 16, 2015 at 16:58

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