Octahedral
A molecular geometry with six bonds arranged symmetrically around a central atom, like the vertices of an octahedron. Bond angles are 90°. Common in transition metal complexes with…
Chemical Glossary — Letter O
43 chemicals found starting with "O"
Octane Number
The octane number (octane rating) is a measure of a fuel's resistance to knocking (premature detonation) in a spark-ignition internal combustion engine, with higher values indicati…
Octet Rule
The octet rule states that atoms of main-group elements tend to gain, lose, or share electrons to achieve a configuration with eight electrons in their valence shell, analogous to …
Octet Rule
The tendency of atoms to gain, lose, or share electrons until they have eight valence electrons, achieving a stable noble gas configuration. The rule explains the formation of ioni…
Oganesson
Oganesson is a synthetic radioactive element and the heaviest known element, named after physicist Yuri Oganessian. First synthesised in 2002 at Dubna. Despite being in the noble g…
Oil
In chemistry, oils are hydrophobic, viscous liquid mixtures of organic compounds — primarily long-chain hydrocarbons, triglycerides (fatty acid esters of glycerol), or mineral hydr…
Open Sextet
An open sextet describes the electronic configuration of certain atoms in molecules (particularly boron and aluminum compounds) that have only six electrons in the valence shell of…
Open System
An open system in thermodynamics is a system that can exchange both matter and energy with its surroundings. This is in contrast to a closed system (exchanges energy but not matter…
Optical Activity
Optical activity is the ability of a chiral substance to rotate the plane of polarization of plane-polarized light. Enantiomers rotate light by equal amounts in opposite directions…
Optical Isomers
Optical isomers (enantiomers) are non-superimposable mirror-image molecules that are identical in all physical properties except for the direction in which they rotate plane-polari…
Optical Isomers
Stereoisomers that are non-superimposable mirror images (enantiomers) or differ in the configuration of one or more chiral centers while having the same connectivity (diastereomers…
Orbital
A mathematical function describing the wave-like behavior of an electron in an atom (atomic orbital) or molecule (molecular orbital). The square of the orbital function gives the p…
Orbital Hybridization
Orbital hybridization is the mixing of atomic orbitals of similar energies to form new hybrid orbitals with different shapes and energies, better suited for bonding. Hybridization …
Order of Reaction
The power to which the concentration of a reactant is raised in the experimentally determined rate law. Overall order is the sum of individual orders. Zero order: rate independent …
Ore
An ore is a naturally occurring rock or mineral from which a valuable metal or mineral can be extracted profitably. Ores consist of the desired mineral mixed with unwanted rock (ga…
Organic Chemistry
Organic chemistry is the branch of chemistry that studies the structure, properties, reactions, and synthesis of organic compounds — those primarily based on carbon-carbon and carb…
Organic Chemistry
The branch of chemistry that studies carbon-containing compounds, including their structure, properties, reactions, and synthesis. Organic chemistry encompasses hydrocarbons, funct…
Organic Compound
A compound primarily composed of carbon and hydrogen, often also containing oxygen, nitrogen, sulfur, and halogens. Organic compounds form the basis of life and include carbohydrat…
Osmium
Osmium is a hard, lustrous, blue-grey transition metal, atomic number 76. The densest naturally occurring element (22.59 g/cm3). Osmium tetroxide (OsO4) is extremely toxic and vola…
Osmolality
Osmolality is a measure of the osmotic concentration of a solution expressed as the number of osmoles of solute per kilogram of solvent (Osm/kg or mOsm/kg). It is distinct from osm…
Osmosis
Osmosis is the spontaneous movement of solvent molecules (usually water) through a semipermeable membrane from a region of lower solute concentration to a region of higher solute c…
Osmosis
The movement of solvent molecules through a semi-permeable membrane from a region of lower solute concentration to higher solute concentration. Osmotic pressure is the pressure nee…
Osmotic Pressure
Osmotic pressure (π) is the minimum pressure that must be applied to a solution to prevent the inward flow of solvent molecules through a semipermeable membrane from pure solvent. …
Osmotic Pressure
The pressure that must be applied to a solution to prevent osmosis through a semi-permeable membrane. Given by π = MRT (van't Hoff equation), where M is molar concentration and T i…
Ostwald Process
The Ostwald Process is the industrial method for producing nitric acid (HNO₃) from ammonia (NH₃). Developed by Wilhelm Ostwald in 1902, it involves three main steps: (1) catalytic …
Ostwald's Dilution Law
A relationship derived from the equilibrium constant that describes how the degree of dissociation of a weak electrolyte varies with dilution. As concentration decreases, degree of…
Outer Orbital Complex
An outer orbital complex (high-spin complex) is a coordination compound in which the ligand field splitting energy (Δ) is small compared to the electron pairing energy, so d-electr…
Overlap
Orbital overlap is the sharing of space between two atomic orbitals on adjacent atoms, which is required for covalent bond formation. The extent of overlap determines the bond stre…
Overvoltage
The extra voltage required beyond the theoretical decomposition potential to cause electrolysis at a practical rate. Also called overpotential. Overvoltage is particularly large fo…
Oxidation
Oxidation is a chemical process in which a substance loses electrons, resulting in an increase in its oxidation state. In terms of oxygen, oxidation involves the addition of oxygen…
Oxidation
A process involving the loss of electrons, increase in oxidation state, or gain of oxygen. In redox reactions, oxidation always accompanies reduction. The species being oxidized is…
Oxidation Number
The hypothetical charge an atom would have if all bonds were ionic, used to track electron transfer in redox reactions. Rules for assigning oxidation numbers allow systematic ident…
Oxidation Numbers
Oxidation numbers (oxidation states) are hypothetical charges assigned to atoms in molecules or ions according to a set of rules that assume all bonds are ionic. They provide a boo…
Oxidation Reduction Reactions
Oxidation-reduction (redox) reactions are chemical reactions involving the transfer of electrons between substances, in which one reactant is oxidized (loses electrons, increasing …
Oxidation State
The formal charge assigned to an atom in a compound based on a set of rules assuming electron pairs belong to the more electronegative atom. Oxidation states are used to track elec…
Oxidative Phosphorylation
Oxidative phosphorylation is the metabolic process by which cells use enzymes in the mitochondrial inner membrane to oxidize nutrients (via the electron transport chain) to produce…
Oxide
An oxide is a binary compound of oxygen with another element. Metal oxides are generally basic and react with water to form metal hydroxides; non-metal oxides are generally acidic …
Oxide
A binary compound of oxygen with another element. Metal oxides are generally basic and react with acids; non-metal oxides are generally acidic and react with bases. Amphoteric oxid…
Oxidising Agent
A substance that accepts electrons from another substance (the reducing agent) in a redox reaction, causing the other substance to be oxidized. The oxidizing agent itself is reduce…
Oxidizing Agent
A chemical species that gains electrons from another species in a redox reaction, thereby oxidizing that species. The oxidizing agent undergoes reduction (its oxidation state decre…
Oxoacid
An acid containing oxygen, hydrogen, and another element, in which the acidic hydrogen atoms are attached to oxygen atoms. Examples include sulfuric acid (H₂SO₄), nitric acid (HNO₃…
Oxygen
Oxygen is a colourless, odourless diatomic gas, atomic number 8, the most abundant element in Earth crust (46% by mass). Essential for aerobic respiration and combustion. Supports …
Ozone
An allotrope of oxygen with molecular formula O₃. Ozone in the stratosphere absorbs harmful UV radiation, protecting life on Earth. At ground level, it is a pollutant and respirato…
About Chemicals Starting With O
This page lists all chemicals in our database beginning with the letter O. Each entry provides the chemical formula, CAS registry number, physical and chemical properties, common uses, and safety information. Use the alphabetical navigation above to browse other letters, or use the search function to find a specific chemical quickly.
Our chemical glossary covers acids, bases, salts, organic compounds, inorganic compounds, solvents, and many more categories. Click on any chemical name to view its full detailed profile.