Reference for all cadmium oxidation states (0, +1, +2) with example compounds, stability context, and a step-by-step compound-to-oxidation-state lookup.
Use the Cadmium Oxidation States
Atomic #48CdCadmium
Atomic Mass
112.411 u
Group
12
Period
5
Block
d-block
Electronegativity
1.69 (Pauling)
Oxidation States
0, +1, +2
Cadmium has three oxidation states. Click a state card to see its compounds,
uses, and how to identify it.
Oxidation State 0
Elemental cadmium carries oxidation state zero by convention — all bonds in a pure element involve identical atoms, so no electron transfer is assigned. Cadmium metal is a soft, bluish-white, ductile solid with a hexagonal close-packed structure. It melts at 321 °C and boils at 767 °C. Historically important as a corrosion-resistant coating for steel (electroplated cadmium), it has been largely phased out in favor of zinc-based coatings due to cadmium's toxicity.
How to Identify This State
Any pure elemental cadmium — cadmium metal rod, powder, or thin film — carries oxidation state 0 by definition. No arithmetic needed.
Example Compounds
Formula
Name
Assignment
Notes
Cd (metal)
Cadmium Metal
Elemental → Cd = 0
Soft, bluish-white metal. Historically used as a corrosion-resistant electroplated coating on steel fasteners and springs.
Cd (vapor)
Cadmium Vapor
Elemental → Cd = 0
Monoatomic vapor at temperatures above 767 °C. Used in cadmium arc lamps and in chemical vapor deposition (CVD) of CdS and CdTe films.
Common Uses
Electroplated corrosion-resistant coating on steel (now largely phased out due to toxicity)
Reference electrode material (cadmium standard cell, historical)
CVD/PVD source material for CdS and CdTe thin films
Alloying: low-melting alloys (Wood's metal) and bearing metals
Oxidation State +1
The +1 state for cadmium is rare and exists only as the Cd₂²⁺ dimer ion — two Cd atoms bonded to each other, each formally carrying +1. This parallels the well-known Hg₂²⁺ (mercury(I)) ion but is far less stable and common. The Cd–Cd bond in Cd₂²⁺ is weaker than the Hg–Hg bond due to the smaller relativistic contraction of 5s orbitals compared to 6s (mercury). Cd₂²⁺ compounds are known only in a few solid-state halometallate salts and decompose readily into Cd(0) and Cd(II) species.
How to Identify This State
In Cd₂²⁺ compounds: assign +1 per Cd by recognizing the dimer structure and the overall 2+ charge on the two-atom unit. The dimer ion is analogous to Hg₂²⁺. Individual Cd atoms in the dimer each formally hold +1. The ion is not Cd+ (monomeric) — always the Cd–Cd bonded pair.
Example Compounds
Formula
Name
Assignment
Notes
Cd2[AlCl4]2
Cadmium(I) Tetrachloroaluminate
Cd–Cd bond + 2(AlCl₄⁻) → each Cd = +1
Solid-state compound with Cd₂²⁺ dimer. Prepared from Cd metal and CdCl₂ in AlCl₃ melt. Decomposes above ~100 °C.
Cd2[GaCl4]2
Cadmium(I) Tetrachlorogallate
Cd–Cd bond + 2(GaCl₄⁻) → each Cd = +1
Analogous to the aluminate salt; confirms Cd₂²⁺ dimer by X-ray crystallography.
Common Uses
No practical applications — purely of academic interest as evidence of Cd–Cd bonding
Model system for comparing Group 12 metal–metal bond stability (Zn < Cd < Hg)
Solid-state inorganic chemistry research
Oxidation State +2
The +2 state is by far the dominant oxidation state of cadmium. Removing both 5s electrons gives Cd²⁺ with a completely filled 4d¹⁰ shell — a very stable, diamagnetic configuration isoelectronic with In³⁺ and Ag⁺ (which has 4d¹⁰). Cd²⁺ is a soft Lewis acid (HSAB) and prefers binding to soft donors such as sulfur (S²⁻, RS⁻) and nitrogen, explaining why cadmium concentrates in sulfide ores and why CdS is the archetypal Cd²⁺ compound. Key examples include cadmium sulfide (CdS, a yellow/orange pigment and semiconductor), cadmium telluride (CdTe, used in thin-film solar cells), cadmium chloride, and cadmium oxide.
How to Identify This State
In CdCl₂: Cl = -1 (2 atoms × -1 = -2); compound is neutral → Cd = +2. In CdS: S = -2; compound is neutral → Cd = +2. In CdO: O = -2; compound is neutral → Cd = +2. In Cd(NO₃)₂: NO₃⁻ is -1 each; two ions total -2; compound neutral → Cd = +2.
Example Compounds
Formula
Name
Assignment
Notes
CdS
Cadmium Sulfide
S = -2, CdS neutral → Cd = +2
Bright yellow/orange semiconductor pigment (Cadmium Yellow). Wurtzite and zinc-blende polymorphs. Used in photovoltaics (CIGS partner layer) and quantum dots.
CdTe
Cadmium Telluride
Te = -2, CdTe neutral → Cd = +2
Thin-film solar cell absorber with 1.45 eV bandgap, near-ideal for single-junction AM1.5 solar spectrum. The dominant thin-film PV technology commercially (First Solar).
CdO
Cadmium Oxide
O = -2, CdO neutral → Cd = +2
Black or brown semiconductor oxide used as a transparent conducting oxide (TCO) in thin films, electrodes, and solar cell buffer layers.
CdCl2
Cadmium Chloride
Cl = -1 (×2 = -2), neutral → Cd = +2
White crystalline salt, highly soluble in water. Layered crystal structure (CdCl₂ structure type, a reference polytype in solid-state chemistry). Used in electroplating baths and as a laboratory reagent.
Cd(NO3)2
Cadmium Nitrate
2(NO₃⁻ = -1) = -2, neutral → Cd = +2
Highly soluble salt used in electrochemistry, nuclear reactor control rods (cadmium absorbs neutrons), and cadmium plating solutions.
Common Uses
CdS and CdSe quantum dots for bioimaging, displays (QLED TVs), and photovoltaics
CdTe thin-film solar cells (commercially dominant thin-film PV technology)
Cadmium Yellow and Cadmium Red artist pigments (CdS, CdSe)
NiCd rechargeable batteries (CdO or Cd(OH)₂ as the negative electrode)
Nuclear reactor control rods (cadmium absorbs thermal neutrons strongly)
Select a compound from the list to see the oxidation state of cadmium
with a step-by-step calculation.
Select a compound to see the oxidation state calculation.
Oxidation state of Cd:
Step-by-step
Oxidation State Summary
State
Stability
Key Example
Notes
0
Elemental
Cd (metal)
Assigned by convention to elemental cadmium in all allotropic forms.
+1
Very Rare
Cd2[AlCl4]2
Exists only as the Cd₂²⁺ dimer in solid-state halometallate salts; decomposes easily.
+2
Dominant
CdS, CdTe, CdCl2
The overwhelmingly dominant state; 4d¹⁰ Cd²⁺ is stable, soft Lewis acid, prefers S and N donors.
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Summary
Cadmium (Cd, atomic number 48) is a Group 12 d-block metal in Period 5 with the ground-state electron configuration [Kr] 4d¹⁰ 5s². Its chemistry is dominated by the +2 state, formed by loss of both 5s electrons to give the stable 4d¹⁰ Cd²⁺ ion — isoelectronic with In³⁺ and Sn⁴⁺. A rare +1 state appears in the Cd₂²⁺ dimer (analogous to Hg₂²⁺) in a handful of solid-state compounds. Elemental cadmium carries oxidation state 0 by convention. Cd²⁺ is soft according to HSAB theory, preferring sulfur and nitrogen ligands, which explains the prevalence of cadmium sulfide, cadmium telluride, and cadmium-thiolate complexes in both nature and technology.
How it works
Click an oxidation state card (0, +1, or +2) to open its detail panel.
The detail panel shows a description, example compounds, step-by-step assignment, and identification tips.
Use the Compound Lookup tab to select a known cadmium compound and see the oxidation state of Cd explained step by step.
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Switch between the Explorer and Compound Lookup tabs using the tab bar.
Use cases
Students revising d-block chemistry and oxidation state rules for exams.
Chemistry teachers preparing reference materials on Group 12 elements.
Materials scientists checking the oxidation state of cadmium in CdS or CdTe for solar cell work.
Toxicologists and environmental chemists identifying cadmium species in contaminated water or soil.
Learners comparing oxidation-state trends across Group 12 (Zn, Cd, Hg).
Frequently Asked Questions
Cadmium exhibits three oxidation states: 0 (elemental metal), +1 (rare, in the Cd₂²⁺ dimer), and +2 (by far the most common and most stable). The +2 state arises from loss of both 5s electrons, leaving the completely filled 4d¹⁰ shell intact.
Cadmium's electron configuration is [Kr] 4d¹⁰ 5s². Removing the two 5s electrons gives Cd²⁺ with a full 4d¹⁰ shell — a particularly stable arrangement (similar to the stability of Zn²⁺ with a full 3d¹⁰ shell). Accessing a +4 state would require breaking into the filled 4d shell, which costs far more energy than is recovered by bond formation.
Cd(+1) appears as the Cd₂²⁺ dimer ion in a small number of solid-state compounds (e.g., Cd₂[AlCl₄]₂ and Cd₂[GaCl₄]₂). Each Cd atom formally carries +1, held together by a Cd–Cd bond. This is analogous to the well-known Hg₂²⁺ ion in mercury(I) compounds but is far less common and less stable for cadmium.
Chlorine is -1 in metal chlorides. Two Cl atoms give -2 total. The compound is neutral: Cd + 2(-1) = 0 → Cd = +2.
Sulfur in binary metal sulfides is -2. The compound is neutral with a 1:1 ratio: Cd + (-2) = 0 → Cd = +2. CdS (cadmium sulfide) is a bright yellow pigment and an important semiconductor.
Negative oxidation states for cadmium are not observed under normal chemical conditions. Unlike main-group elements, cadmium does not gain electrons to fill its 5p shell. Its chemistry is entirely cationic — +2 overwhelmingly, +1 rarely in solid-state dimer compounds, and 0 only in the elemental metal.
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