Read the formula. Understand the substance.
Search the reviewed compound library by name, formula, element or type. Each page connects formula notation to bonding, molar mass, reactions, deeper chemistry, safety context and the element guides behind the formula.
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A reviewed collection of compound learning hubs, expanded in research-driven batches. Each page starts with the essentials and then opens into compound-specific structure, reactions, worked examples and deeper chemistry.
Water
Water is the molecular compound H₂O: each molecule contains two hydrogen atoms covalently bonded to one oxygen atom. The molecule is bent and polar, with two lone pairs on oxygen; that simple structure connects to hydrogen bonding, solvent behavior, acid–base chemistry and water’s unusual phase properties.
Carbon Dioxide
Carbon dioxide is CO₂, a molecular compound containing one carbon atom and two oxygen atoms per molecule. The equilibrium molecule is linear: each C=O bond is polar, but the two bond dipoles point in opposite directions and cancel, so CO₂ has no permanent molecular dipole.
Sodium Chloride
Sodium chloride is the ionic compound NaCl. In an ordinary crystal there are no separate NaCl molecules: NaCl gives the simplest 1:1 ratio of sodium ions (Na⁺) to chloride ions (Cl⁻) in an extended lattice. That distinction explains its crystal structure, conductivity, dissolution and electrochemistry.
Ammonia
Ammonia is NH₃, a polar molecular compound with three N–H bonds and one lone pair on nitrogen. Those four electron domains give a trigonal-pyramidal molecule, and the lone pair is the key to both its shape and its ability to act as a Brønsted and Lewis base.
Methane
Methane is CH₄, the simplest hydrocarbon. One carbon atom forms four C–H bonds in a tetrahedral arrangement. The symmetric geometry gives the molecule no permanent dipole and provides a clean starting point for learning carbon valence, combustion and hydrocarbon chemistry.
Calcium Carbonate
Calcium carbonate is CaCO₃, an ionic solid made from Ca²⁺ and CO₃²⁻ in a 1:1 formula-unit ratio. The carbonate ion is internally covalent and resonance-stabilized, while calcium and carbonate ions form the crystal lattice. That layered bonding picture connects directly to polymorphs, acid fizzing, scale and lime/cement chemistry.
Sulfuric Acid
Sulfuric acid is H₂SO₄, a diprotic oxoacid with two ionizable hydrogens. In water, the first proton transfer is essentially complete, while hydrogen sulfate (HSO₄⁻) has a distinct second ionization equilibrium. Concentrated sulfuric acid is also a very different chemical environment from a dilute aqueous solution.
Hydrochloric Acid
HCl is hydrogen chloride as a pure molecular substance; when dissolved in water it forms hydrochloric acid, a strong-acid solution in which HCl is essentially converted to hydrated hydronium and chloride ions. Keeping the gas and the aqueous acid distinct resolves many common misconceptions.
Silicon Dioxide
Silicon dioxide, SiO₂, is the composition of silica. In ordinary quartz and silica glass it is not a collection of discrete O=Si=O molecules: silicon and oxygen form an extended network in which Si is commonly tetrahedrally coordinated by O, and oxygens bridge between silicon centers.
Sodium Hydroxide
Sodium hydroxide, NaOH, is an ionic solid made from Na⁺ and OH⁻ ions. When it dissolves in water it dissociates essentially completely, so it is classified as a strong base. “Strong base” describes this dissociation/acid–base behavior; it does not tell you the concentration of a particular solution.
Hydrogen Peroxide
Hydrogen peroxide is H₂O₂, a molecular peroxide with an O–O single bond. Its oxygen atoms have oxidation state −1—between oxygen in water (−2) and elemental O₂ (0)—which helps explain why H₂O₂ can participate in both oxidation and reduction chemistry and can disproportionate to water and oxygen.
Ethanol
Ethanol is the two-carbon alcohol CH₃CH₂OH, with molecular formula C₂H₆O. The structural formula matters because C₂H₆O can also describe the different compound dimethyl ether. Ethanol’s hydroxyl group makes it polar, hydrogen-bonding and much more water-compatible than a comparable hydrocarbon.
Carbon Monoxide
Carbon monoxide is CO, a neutral diatomic molecule containing one carbon atom and one oxygen atom. Its familiar Lewis structure has a C≡O triple bond with one lone pair on each atom and formal charges C⁻ and O⁺. CO is a very different substance from carbon dioxide, CO₂.
Sodium Bicarbonate
Sodium bicarbonate is NaHCO₃, an ionic solid made from Na⁺ and HCO₃⁻ ions in a 1:1 ratio. The bicarbonate ion is amphiprotic: it can accept a proton to move toward carbonic acid or donate one to form carbonate. This is the chemistry behind its buffering and acid-reactive behavior.
Acetic Acid
Acetic acid, also called ethanoic acid, has molecular formula C₂H₄O₂ and is commonly written structurally as CH₃COOH. It is a weak carboxylic acid: in water it establishes an equilibrium with acetate and hydronium rather than ionizing essentially completely like HCl.
Nitric Acid
Nitric acid is HNO₃, a strong monoprotic oxoacid of nitrogen. In water it ionizes essentially completely in ordinary general-chemistry treatment, forming hydronium and nitrate. Nitric acid is also a strong oxidizing reagent, so its chemistry with metals cannot be reduced to the usual “acid gives hydrogen gas” rule.
Glucose
Glucose is C₆H₁₂O₆, a six-carbon monosaccharide and aldohexose. The molecular formula alone does not capture its stereochemistry. In water, D-glucose exists mainly as cyclic α- and β-D-glucopyranose forms that interconvert through a small amount of open-chain aldehyde.
Copper(II) Sulfate
Copper(II) sulfate is CuSO₄, an ionic salt containing Cu²⁺ and SO₄²⁻ in a 1:1 ratio. The anhydrous salt and the familiar blue pentahydrate, CuSO₄·5H₂O, are different solid forms with different formula masses and crystal structures.
Sodium Carbonate
Sodium carbonate is Na₂CO₃, an ionic carbonate salt made from two Na⁺ ions for each CO₃²⁻ ion. The carbonate ion has delocalized bonding, and aqueous sodium carbonate is basic because CO₃²⁻ accepts a proton from water to form HCO₃⁻ and OH⁻.
Phosphoric Acid
Phosphoric acid is H₃PO₄, a phosphorus oxoacid with three ionizable O–H groups. It is triprotic: proton loss occurs stepwise through H₂PO₄⁻, HPO₄²⁻ and PO₄³⁻, with each successive deprotonation less favorable in water.
Calcium Hydroxide
Calcium hydroxide is Ca(OH)₂, an ionic solid containing Ca²⁺ and OH⁻ in a 1:2 ratio. It is a strong base in the sense that dissolved Ca(OH)₂ dissociates into ions, but it is only sparingly soluble, so strength and solubility must not be confused.
Ammonium Chloride
Ammonium chloride is NH₄Cl, an ionic salt made from NH₄⁺ and Cl⁻. In water, NH₄⁺ can donate a proton to water while Cl⁻ has negligible basicity, so the solution is acidic.
Potassium Permanganate
Potassium permanganate is KMnO₄, an ionic solid composed of K⁺ and MnO₄⁻. Manganese is +7 and the permanganate ion is approximately tetrahedral. Its intense purple color and strong oxidizing behavior make it a central redox compound.
Sulfur Dioxide
Sulfur dioxide is SO₂, a bent, polar molecular gas containing sulfur in oxidation state +4. Lewis structures use resonance contributors; VSEPR gives trigonal-planar electron-domain geometry and a bent molecular shape.
Acetone
Acetone is C₃H₆O, more informatively written (CH₃)₂CO. It is the simplest common ketone: a carbonyl carbon bonded to two methyl groups. The C=O bond is strongly polar, making acetone a polar aprotic solvent.
Benzene
Benzene is C₆H₆, a planar six-carbon aromatic ring with six delocalized π electrons. It is not accurately described as a ring with three fixed single and three fixed double bonds: all six C–C bonds are equivalent in the real molecule.
What a useful compound page should answer
What does the formula mean, and how many atoms or ions does it represent?
Is it molecular, ionic or an extended structure—and what bonding model fits?
Which elements, reactions, molar-mass calculations and chemistry lessons connect to it?
What changes at university or engineering depth: equilibria, materials, process context or evidence limits?
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