What are the oxidation states of tin?

Tin has four known oxidation states: +4 (stannic), +2 (stannous), 0 (elemental), and −4 (rare, in stannide intermetallics). Both +4 and +2 are stable and common in ordinary chemistry, which makes tin unusual among Period 5 elements.

What is the inert pair effect in tin?

In Period 5 (and Period 6) p-block metals, the 5s² electron pair becomes increasingly reluctant to participate in bonding because relativistic contraction draws the 5s orbital closer to the nucleus, lowering its energy. This "inert pair" remains non-bonding, stabilizing the +2 state (5s² 5p⁰) even though the full +4 state (5s⁰ 5p⁰) is often more stable thermodynamically.

Is tin +2 or +4 more stable?

It depends on conditions. SnO₂ (+4) is thermodynamically more stable than SnO (+2) at room temperature. However, the +2 state is kinetically stable due to the inert pair effect, and Sn²⁺ compounds such as SnCl₂ are widely used in practice. In solution, Sn²⁺ is a mild reducing agent that can be oxidized to Sn⁴⁺.

What is stannous chloride used for?

Stannous chloride (SnCl₂) is a mild reducing agent used to reduce mercury(II) to mercury in qualitative analysis, to silver mirrors in the Tollen's test setup, and as a reducing agent in organic synthesis. It is also used as a food additive (E512) and in electroplating.

What is stannic oxide (SnO₂) used for?

Stannic oxide (SnO₂, cassiterite) is tin's most commercially important compound. It is used as a transparent conductor in glass coatings (ITO glass alternative), as a polishing powder for metals and glass, as a ceramic pigment (opacifier), and in gas sensors. Cassiterite is the primary ore of tin.

Does tin have a −4 oxidation state?

Yes, but it is rare. The −4 state appears in stannide compounds such as Na₄Sn or intermetallic phases where tin accepts electrons from electropositive metals. It is not accessible under ordinary laboratory conditions.

Tin Oxidation States

Name: Tin Oxidation States
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Author: Nham Vu

Reference for tin (Sn, Z=50) oxidation states (+4, +2, 0, −4), stability, electron configuration, and compounds including stannous and stannic forms.

Atomic # 50 Sn Tin

Atomic Mass

118.710 u

Group

14 (IVA)

Period

Block

p-block

Electronegativity

1.96 (Pauling)

Oxidation States

+4, +2, 0, −4

Tin has four oxidation states: +4 (stannic), +2 (stannous), 0, and −4. Both +4 and +2 are encountered in everyday chemistry — an unusual trait for a metal. Tin's electron configuration is [Kr] 4d¹⁰ 5s² 5p². The +4 state uses all four valence electrons (5s²5p²), while the +2 state leaves the 5s² pair unused — a phenomenon called the inert pair effect, which becomes significant in heavier p-block elements.

Inert Pair Effect
In Period 5 p-block metals, the 5s² electrons are drawn closer to the nucleus by relativistic contraction and poor shielding by the filled 4d¹⁰ shell. This lowers their energy and makes them resistant to ionization, stabilizing the +2 state alongside the expected +4 state.

Oxidation State	Name	Stability	Notes
+4	Stannic	Common — thermodynamically stable	Uses all four valence electrons (5s²5p²). Found in SnO₂ (cassiterite, the principal tin ore), SnCl₄, and SnF₄. SnO₂ is the thermodynamically preferred oxide at room temperature.
+2	Stannous	Common — inert pair stabilized	Leaves the 5s² pair intact (inert pair effect). Found in SnCl₂ (stannous chloride, a mild reducing agent), SnO, SnF₂ (in toothpaste). Sn²⁺ can be oxidized to Sn⁴⁺ in solution.
0	Elemental	Elemental only	Elemental tin exists as white tin (β-Sn, body-centered tetragonal, stable above 13.2 °C) and gray tin (α-Sn, diamond cubic, stable below 13.2 °C). Standard reduction potential Sn²⁺/Sn = −0.14 V.
−4	Stannide	Very rare — intermetallics only	Occurs in stannide phases where electropositive metals (e.g., Na, Ca) donate electrons to tin, forming Sn⁴⁻ (analogous to carbide or silicide). Found in intermetallic compounds such as Na₄Sn. No practical laboratory chemistry.

Reduction Potentials
Sn⁴⁺/Sn²⁺: +0.15 V | Sn²⁺/Sn: −0.14 V
Sn²⁺ is a mild reducing agent — it can reduce Hg²⁺, Fe³⁺, and I₂ under standard conditions. The modest Sn⁴⁺/Sn²⁺ potential means moderate oxidants push Sn²⁺ to Sn⁴⁺.

Tin forms stable compounds in both the +2 (stannous) and +4 (stannic) oxidation states. The +4 compounds tend to be more covalent (e.g., SnCl₄ is a liquid), while +2 compounds are more ionic (SnCl₂ is a solid salt). SnO₂ (cassiterite) is the principal ore and the most commercially significant tin compound.

Compound	Formula	Sn State	Notes
Stannic Oxide (Cassiterite)	SnO₂	+4	White solid; the principal tin ore and most stable tin compound. Used in glass coatings (transparent conductor), ceramic opacifiers, gas sensors, and polishing compounds.
Stannic Chloride	SnCl₄	+4	Colorless fuming liquid (bp 114 °C); highly covalent. Hydrolyzes in water to form stannic acid. Used as a Lewis acid catalyst and in making organotin compounds.
Stannic Fluoride	SnF₄	+4	White solid; polymeric structure with bridging fluorides. Less common than SnF₂ but used in certain fluorination reactions.
Stannic Sulfide	SnS₂	+4	Golden-yellow solid with a CdI₂ layer structure. Used as a gold-colored pigment ("mosaic gold") and as a 2D semiconductor material in research.
Stannous Chloride	SnCl₂	+2	White solid salt; the most common Sn²⁺ reagent. Mild reducing agent used in qualitative analysis (reducing Hg²⁺ to Hg), electroplating baths, and as a food additive (E512).
Stannous Oxide	SnO	+2	Blue-black solid with unusual lone-pair-directed structure. Used in glass manufacturing and as a precursor to other Sn²⁺ compounds.
Stannous Fluoride	SnF₂	+2	White solid; readily available and soluble. Added to some toothpastes (stannous fluoride toothpaste) for caries prevention alongside fluoride delivery.
Stannous Sulfide	SnS	+2	Gray-black solid with a layered structure; a p-type semiconductor investigated for photovoltaic applications.
Stannous Sulfate	SnSO₄	+2	White solid; used in electroplating (electrolytic tinning of steel) as a source of Sn²⁺ ions.
Tin(IV) Hydride (Stannane)	SnH₄	+4	Colorless gas; thermally unstable above −52 °C. A chemical vapor deposition precursor for tin oxide films. Toxic.

Ground State Configuration

Inert pair — retained in Sn²⁺; released in Sn⁴⁺

Two valence p-electrons — released in both Sn²⁺ and Sn⁴⁺

Notation

Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p²

Noble gas: [Kr] 4d¹⁰ 5s² 5p²

Sn²⁺ ion: [Kr] 4d¹⁰ 5s²

Sn⁴⁺ ion: [Kr] 4d¹⁰

Note: the retained 5s² lone pair in Sn²⁺ is stereochemically active — it influences bond angles in compounds like SnCl₂ (bent, ~95°).

Ionization Steps

[Kr] 4d¹⁰ 5s² 5p²

Neutral atom — four valence electrons

Sn²⁺

[Kr] 4d¹⁰ 5s²

Remove two 5p electrons. IE₁ 708.6, IE₂ 1411.8 kJ/mol. Stannous state — inert 5s² pair retained.

Sn⁴⁺

[Kr] 4d¹⁰

Remove two more 5s electrons. IE₃ 2943, IE₄ 3930 kJ/mol. Stannic state — fully stripped valence shell.

Ionization Energies
IE₁ = 708.6 kJ/mol | IE₂ = 1411.8 kJ/mol
IE₃ = 2943 kJ/mol | IE₄ = 3930 kJ/mol
The large jump from IE₂ to IE₃ reflects the energy cost of removing 5s electrons from the inert pair — the structural reason both +2 and +4 states are accessible.

Comparing +2 vs +4 stability
SnO₂ is thermodynamically more stable than SnO at room temperature (more negative ΔG°). Yet SnCl₂ is a practical, bench-stable reagent because the kinetic stability from the inert pair effect slows oxidation under ordinary conditions. In solution, Sn²⁺ reduces easily oxidizable substrates; in the solid state, +2 compounds are less sensitive.

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Summary

Reference for tin (Sn, Z=50) oxidation states (+4, +2, 0, −4), stability, electron configuration, and compounds including stannous and stannic forms.

How it works

Click a tab — Oxidation States, Compounds, Electron Config, or Physical Props — to explore each section.
The Oxidation States panel explains the inert pair effect and tabulates +4, +2, 0, and −4 with stability notes.
The Compounds panel lists stannous (Sn²⁺) and stannic (Sn⁴⁺) compounds with formulas and practical uses.
The Electron Config panel shows orbital filling and ionization steps from Sn to Sn²⁺ and Sn⁴⁺.
The Physical Props panel provides atomic mass, melting point, density, and other reference data.
Click any monospace table cell to copy its value to your clipboard.

Use cases

Students studying p-block chemistry and the inert pair effect in Period 5 elements.
Chemistry teachers preparing lessons on tin, Group 14, or post-transition metal behavior.
Lab chemists working with stannous chloride (reducing agent) or stannic oxide (coatings).
Engineers selecting tin alloys or understanding tin corrosion behavior.
Anyone preparing for chemistry exams covering Period 5 or Group 14 elements.

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Last updated: 2026-07-08 · Reviewed by Nham Vu