Water

A water molecule consists of two hydrogen atoms and one oxygen atom
The three common states of matter
Phase diagram of water (simplified)
Tetrahedral structure of water
Model of hydrogen bonds (1) between molecules of water
Water cycle
Overview of photosynthesis (green) and respiration (red)
Water fountain
An environmental science program – a student from Iowa State University sampling water
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m³) per year in 2010
A young girl drinking bottled water
Water availability: the fraction of the population using improved water sources by country
Roadside fresh water outlet from glacier, Nubra
Hazard symbol for non-potable water
Water is used for fighting wildfires.
San Andrés island, Colombia
Water can be used to cook foods such as noodles
Sterile water for injection
Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.
South polar ice cap of Mars during Martian south summer 2000
An estimate of the proportion of people in developing countries with access to potable water 1970–2000
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water
Icosahedron as a part of Spinoza monument in Amsterdam.
Water requirement per tonne of food product
Irrigation of field crops
Specific heat capacity of water

Inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent ).

- Water
A water molecule consists of two hydrogen atoms and one oxygen atom

139 related topics

Alpha

NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted

Atmosphere of Earth

Layer of gases retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere.

Layer of gases retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere.

NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted
Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations ). Numbers are mainly from 2000, with and methane from 2019, and do not represent any single source.
Mean atmospheric water vapor
The mole fraction of the main constituents of the Earth's atmosphere as a function of height according to the MSIS-E-90 atmospheric model.
Earth's atmosphere Lower 4 layers of the atmosphere in 3 dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.
orbiting in the thermosphere. Because of the angle of the photo, it appears to straddle the stratosphere and mesosphere that actually lie more than 250 km below. The orange layer is the troposphere, which gives way to the whitish stratosphere and then the blue mesosphere.
Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on NOAA weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:
Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)
Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.
Distortive effect of atmospheric refraction upon the shape of the sun at the horizon.
An idealised view of three pairs of large circulation cells.
Oxygen content of the atmosphere over the last billion years

The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

The formation of a spherical droplet of liquid water minimizes the surface area, which is the natural result of surface tension in liquids.

Liquid

Nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure.

Nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure.

The formation of a spherical droplet of liquid water minimizes the surface area, which is the natural result of surface tension in liquids.
Thermal image of a sink full of hot water with cold water being added, showing how the hot and the cold water flow into each other.
A lava lamp contains two immiscible liquids (a molten wax and a watery solution) which add movement due to convection. In addition to the top surface, surfaces also form between the liquids, requiring a tension breaker to recombine the wax droplets at the bottom.
Surface waves in water
A simulation of viscosity. The fluid on the left has a lower viscosity and Newtonian behavior while the liquid on the right has higher viscosity and non-Newtonian behavior.
A typical phase diagram. The dotted line gives the anomalous behaviour of water. The green lines show how the freezing point can vary with pressure, and the blue line shows how the boiling point can vary with pressure. The red line shows the boundary where sublimation or deposition can occur.
Structure of a classical monatomic liquid. Atoms have many nearest neighbors in contact, yet no long-range order is present.
Radial distribution function of the Lennard-Jones model fluid.

Water is by far the most common liquid on Earth.

Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)

Atom

Smallest unit of ordinary matter that forms a chemical element.

Smallest unit of ordinary matter that forms a chemical element.

Atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy vol. 1 (1808)
The Geiger–Marsden experiment:
Left: Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection.
Right: Observed results: a small portion of the particles were deflected by the concentrated positive charge of the nucleus.
The Bohr model of the atom, with an electron making instantaneous "quantum leaps" from one orbit to another with gain or loss of energy. This model of electrons in orbits is obsolete.
The binding energy needed for a nucleon to escape the nucleus, for various isotopes
A potential well, showing, according to classical mechanics, the minimum energy V(x) needed to reach each position x. Classically, a particle with energy E is constrained to a range of positions between x1 and x2.
3D views of some hydrogen-like atomic orbitals showing probability density and phase (g orbitals and higher are not shown)
This diagram shows the half-life (T½) of various isotopes with Z protons and N neutrons.
These electron's energy levels (not to scale) are sufficient for ground states of atoms up to cadmium (5s2 4d10) inclusively. Do not forget that even the top of the diagram is lower than an unbound electron state.
An example of absorption lines in a spectrum
Graphic illustrating the formation of a Bose–Einstein condensate
Scanning tunneling microscope image showing the individual atoms making up this gold (100) surface. The surface atoms deviate from the bulk crystal structure and arrange in columns several atoms wide with pits between them (See surface reconstruction).
Periodic table showing the origin of each element. Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture (s-process). Elements heavier than iron may be made in neutron star mergers or supernovae after the r-process.

At the surface of the Earth, an overwhelming majority of atoms combine to form various compounds, including water, salt, silicates and oxides.

Crystal structure of dry ice

Carbon dioxide

Chemical compound occurring as a colorless gas with a density about 53% higher than that of dry air.

Chemical compound occurring as a colorless gas with a density about 53% higher than that of dry air.

Crystal structure of dry ice
Stretching and bending oscillations of the CO2 carbon dioxide molecule. Upper left: symmetric stretching. Upper right: antisymmetric stretching. Lower line: degenerate pair of bending modes.
Pellets of "dry ice", a common form of solid carbon dioxide
Pressure–temperature phase diagram of carbon dioxide. Note that it is a log-lin chart.
Carbon dioxide bubbles in a soft drink
Dry ice used to preserve grapes after harvest
Use of a CO2 fire extinguisher
Comparison of the pressure–temperature phase diagrams of carbon dioxide (red) and water (blue) as a log-lin chart with phase transitions points at 1 atmosphere
A carbon-dioxide laser
Keeling curve of the atmospheric CO2 concentration
Atmospheric CO2 annual growth rose 300% since the 1960s.
Annual flows from anthropogenic sources (left) into Earth's atmosphere, land, and ocean sinks (right) since the 1960s. Units in equivalent gigatonnes carbon per year.
Pterapod shell dissolved in seawater adjusted to an ocean chemistry projected for the year 2100.
Overview of the Calvin cycle and carbon fixation
Overview of photosynthesis and respiration. Carbon dioxide (at right), together with water, form oxygen and organic compounds (at left) by photosynthesis, which can be respired  to water and (CO2).
Symptoms of carbon dioxide toxicity, by increasing volume percent in air.
Rising levels of CO2 threatened the Apollo 13 astronauts who had to adapt cartridges from the command module to supply the carbon dioxide scrubber in the Lunar Module, which they used as a lifeboat.
CO2 concentration meter using a nondispersive infrared sensor

Photosynthesis uses carbon dioxide and water to produce sugars from which other organic compounds can be constructed, and oxygen is produced as a by-product.

Ice

The three-dimensional crystal structure of H2O ice Ih (c) is composed of bases of H2O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).
Pressure dependence of ice melting
Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.
An alternative formulation of the phase diagram for certain ices and other phases of water
Frozen waterfall in southeast New York
Feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F).
Ice on deciduous tree after freezing rain
A small frozen rivulet
Ice formation on exterior of vehicle windshield
An accumulation of ice pellets
A large hailstone, about 6 cm in diameter
Snowflakes by Wilson Bentley, 1902.
Harvesting ice on Lake St. Clair in Michigan, c. 1905
Layout of a late 19th-Century ice factory
Loss of control on ice by an articulated bus
Channel through ice for ship traffic on Lake Huron with ice breakers in background
Rime ice on the leading edge of an aircraft wing, partially released by the black pneumatic boot.
Skating fun by 17th century Dutch painter Hendrick Avercamp
Ice pier during 1983 cargo operations. McMurdo Station, Antarctica

Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or 32 degrees Fahrenheit.

The unit cell of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen.

Oxide

Chemical compound that contains at least one oxygen atom and one other element in its chemical formula.

Chemical compound that contains at least one oxygen atom and one other element in its chemical formula.

The unit cell of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen.
Oxides, such as iron(III) oxide or rust, which consists of hydrated iron(III) oxides Fe2O3·nH2O and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), form when oxygen combines with other elements
Carbon dioxide is the main product of fossil fuel combustion.
Carbon monoxide is the product of the incomplete combustion of carbon-based fuels and a precursor to many useful chemicals.
Nitrogen dioxide is a problematic pollutant from internal combustion engines.
Sulfur dioxide, the principal oxide of sulfur, is emitted from volcanoes.
Nitrous oxide ("laughing gas") is a potent greenhouse gas produced by soil bacteria.

Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water.

Carl Wilhelm Scheele, discoverer of chlorine

Chlorine

Chemical element with the symbol Cl and atomic number 17.

Chemical element with the symbol Cl and atomic number 17.

Carl Wilhelm Scheele, discoverer of chlorine
Chlorine, liquefied under a pressure of 7.4 bar at room temperature, displayed in a quartz ampule embedded in acrylic glass.
Solid chlorine at −150 °C
Structure of solid deuterium chloride, with D···Cl hydrogen bonds
Hydrated nickel(II) chloride, NiCl2(H2O)6.
Yellow chlorine dioxide (ClO2) gas above a solution containing chlorine dioxide.
Structure of dichlorine heptoxide, Cl2O7, the most stable of the chlorine oxides
Suggested mechanism for the chlorination of a carboxylic acid by phosphorus pentachloride to form an acyl chloride
Liquid chlorine analysis
Membrane cell process for chloralkali production
Ignaz Semmelweis
Liquid Pool Chlorine
Chlorine "attack" on an acetal resin plumbing joint resulting from a fractured acetal joint in a water supply system which started at an injection molding defect in the joint and slowly grew until the part failed; the fracture surface shows iron and calcium salts that were deposited in the leaking joint from the water supply before failure and are the indirect result of the chlorine attack

Chlorination modifies the physical properties of hydrocarbons in several ways: chlorocarbons are typically denser than water due to the higher atomic weight of chlorine versus hydrogen, and aliphatic organochlorides are alkylating agents because chloride is a leaving group.

Schematic of photosynthesis in plants. The carbohydrates produced are stored in or used by the plant.

Photosynthesis

Process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities.

Process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities.

Schematic of photosynthesis in plants. The carbohydrates produced are stored in or used by the plant.
Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
Light-dependent reactions of photosynthesis at the thylakoid membrane
The "Z scheme"
Overview of the Calvin cycle and carbon fixation
Overview of C4 carbon fixation
Plant cells with visible chloroplasts (from a moss, Plagiomnium affine)
Portrait of Jan Baptist van Helmont by Mary Beale, c.1674
Melvin Calvin works in his photosynthesis laboratory.
The leaf is the primary site of photosynthesis in plants.
Absorbance spectra of free chlorophyll a ( blue ) and b ( red ) in a solvent. The action spectra of chlorophyll molecules are slightly modified in vivo depending on specific pigment–protein interactions.
Photorespiration

Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek phōs (φῶς), "light", and sunthesis (σύνθεσις), "putting together".

A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology. Here, A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.

Soil

Mixture of organic matter, minerals, gases, liquids, and organisms that together support life.

Mixture of organic matter, minerals, gases, liquids, and organisms that together support life.

A, B, and C represent the soil profile, a notation firstly coined by Vasily Dokuchaev (1846–1903), the father of pedology. Here, A is the topsoil; B is a regolith; C is a saprolite (a less-weathered regolith); the bottom-most layer represents the bedrock.
Surface-water-gley developed in glacial till in Northern Ireland
Soil profile: Darkened topsoil and reddish subsoil layers are typical of humid subtropical climate regions.
Desertification
Erosion control

Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution).

Sodium and fluorine bonding ionically to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically. The oppositely charged ions are then attracted to each other. The sodium is oxidized; and the fluorine is reduced.

Redox

Type of chemical reaction in which the oxidation states of substrate change.

Type of chemical reaction in which the oxidation states of substrate change.

Sodium and fluorine bonding ionically to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically. The oppositely charged ions are then attracted to each other. The sodium is oxidized; and the fluorine is reduced.
The international pictogram for oxidizing chemicals
Illustration of a redox reaction
A redox reaction is the force behind an electrochemical cell like the Galvanic cell pictured. The battery is made out of a zinc electrode in a ZnSO4 solution connected with a wire and a porous disk to a copper electrode in a CuSO4 solution.
Oxides, such as iron(III) oxide or rust, which consists of hydrated iron(III) oxides Fe2O3·nH2O and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), form when oxygen combines with other elements
Iron rusting in pyrite cubes
Enzymatic browning is an example of a redox reaction that takes place in most fruits and vegetables.
Blast furnaces of Třinec Iron and Steel Works, Czech Republic

The combustion of hydrocarbons, such as in an internal combustion engine, produces water, carbon dioxide, some partially oxidized forms such as carbon monoxide, and heat energy. Complete oxidation of materials containing carbon produces carbon dioxide.