Quantum mechanics including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of energy levels of atoms and subatomic particles.
Classical physics, the physics existing before quantum mechanics, describes nature at ordinary (macroscopic) scale. Most theories in classical physics can be derived from quantum mechanics as an approximation valid at large (macroscopic) scale. Quantum mechanics differs from classical physics in that energy, momentum, angular momentum and other quantities of a system are restricted to discrete values (quantization); objects have characteristics of both particles and waves (wave-particle duality); and there are limits to the precision with which quantities can be measured (uncertainty principle).
Quantum mechanics gradually arose from theories to explain observations which could not be reconciled with classical physics, such as Max Planck’s solution in 1900 to the black-body radiation problem, and from the correspondence between energy and frequency in Albert Einstein’s 1905 paper which explained the photoelectric effect. Early quantum theory was profoundly re-conceived in the mid-1920s by Erwin Schrödinger, Werner Heisenberg, Max Born and others. The modern theory is formulated in various specially developed mathematical formalisms. In one of them, a mathematical function, the wave function, provides information about the probability amplitude of position, momentum, and other physical properties of a particle.
Important applications of quantum theory include quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, and the laser, the transistor and semiconductors such as the microprocessor, medical and research imaging such as magnetic resonance imaging and electron microscopy. Explanations for many biological and physical phenomena are rooted in the nature of the chemical bond, most notably the macro-molecule DNA.
Movement of carbon between land, atmosphere, and ocean in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. The effects of volcanic and tectonic activity are not included.
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major component of many minerals such as limestone. Along with the nitrogen cycle and the water cycle, the carbon cycle comprises a sequence of events that are key to make Earth capable of sustaining life. It describes the movement of carbon as it is recycled and reused throughout the biosphere, as well as long-term processes of carbon sequestration to and release from carbon sinks.
Carbon in the Earth’s atmosphere exists in two main forms: carbon dioxide and methane. Both of these gases absorb and retain heat in the atmosphere and are partially responsible for the greenhouse effect.Methane produces a larger greenhouse effect per volume as compared to carbon dioxide, but it exists in much lower concentrations and is more short-lived than carbon dioxide, making carbon dioxide the more important greenhouse gas of the two.
Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. It can then be absorbed by rocks through weathering. It also can acidify other surfaces it touches or be washed into the ocean.
The terrestrial biosphere includes the organic carbon in all land-living organisms, both alive and dead, as well as carbon stored in soils. About 500 gigatons of carbon are stored above ground in plants and other living organisms, while soil holds approximately 1,500 gigatons of carbon. Most carbon in the terrestrial biosphere is organic carbon, while about a third of soil carbon is stored in inorganic forms, such as calcium carbonate. Organic carbon is a major component of all organisms living on earth. Autotrophs extract it from the air in the form of carbon dioxide, converting it into organic carbon, while heterotrophs receive carbon by consuming other organisms.
Because carbon uptake in the terrestrial biosphere is dependent on biotic factors, it follows a diurnal and seasonal cycle. In CO2 measurements, this feature is apparent in the Keeling curve. It is strongest in the northern hemisphere, because this hemisphere has more land mass than the southern hemisphere and thus more room for ecosystems to absorb and emit carbon.
Nuclear chemistry is the subfield of chemistry dealing with radioactivity, nuclear processes, such as nuclear transmutation, and nuclear properties.
It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. This includes the corrosion of surfaces and the behavior under conditions of both normal and abnormal operation (such as during an accident). An important area is the behavior of objects and materials after being placed into a nuclear waste storage or disposal site.
It includes the study of the chemical effects resulting from the absorption of radiation within living animals, plants, and other materials. The radiation chemistry controls much of radiation biology as radiation has an effect on living things at the molecular scale, to explain it another way the radiation alters the biochemicals within an organism, the alteration of the biomolecules then changes the chemistry which occurs within the organism, this change in chemistry then can lead to a biological outcome. As a result, nuclear chemistry greatly assists the understanding of medical treatments (such as cancer radiotherapy) and has enabled these treatments to improve.
It includes the study of the production and use of radioactive sources for a range of processes. These include radiotherapy in medical applications; the use of radioactive tracers within industry, science and the environment; and the use of radiation to modify materials such as polymers.
It also includes the study and use of nuclear processes in non-radioactive areas of human activity. For instance, nuclear magnetic resonance (NMR) spectroscopy is commonly used in synthetic organic chemistry and physical chemistry and for structural analysis in macromolecular chemistry.
A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Due to their broad range of properties，both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals.
The term “polymer” derives from the Greek word πολύς (polus, meaning “many, much”) and μέρος (meros, meaning “part”), and refers to a molecule whose structure is composed of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant properties。The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition。The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, who spent the next decade finding experimental evidence for this hypothesis.
Polymers are studied in the fields of biophysics and macromolecular science, and polymer science (which includes polymer chemistry and polymer physics). Historically, products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science; emerging important areas of the science now focus on non-covalent links. Polyisoprene of latex rubber is an example of a natural/biological polymer, and the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts, essentially all biological macromolecules—i.e., proteins (polyamides), nucleic acids (polynucleotides), and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e.g., isoprenylated/lipid-modified glycoproteins, where small lipidic molecules and oligosaccharide modifications occur on the polyamide backbone of the protein
In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic covalent bonds to two arene ligands. The arenes have the formula CnHn, substituted derivatives (for example Cn(CH3)n) and heterocyclic derivatives (for example BCnHn+1). Because the metal is usually situated between the two rings, it is said to be “sandwiched”. A special class of sandwich complexes are the metallocenes.
The term sandwich compound was introduced in organometallic nomenclature in the mid-1950s in a report which confirmed the structure of ferrocene by X-ray crystallography. The correct structure had been proposed several years previously by Robert Burns Woodward and, separately, by Ernst Otto Fischer. The structure helped explain puzzles about ferrocene, the molecule features an iron atom sandwiched between two parallel cyclopentadienyl rings. This result further demonstrated the power of X-ray crystallography and accelerated the growth of organometallic chemistry.
The best known members are the metallocenes of the formula M(C5H5)2 where M = Cr, Fe, Co, Ni, Pb, Zr, Ru, Rh, Sm, Ti, V, Mo, W, Zn. These species are also called bis(cyclopentadienyl)metal complexes. Other arenes can serve as ligands as well.
Some mixed cyclopentadienyl complexes are M(C5H5)(CnHn). Some examples are Ti(C5H5)(C7H7) and (C60)Fe(C5H5Ph5) where the fullerene ligand is acting as a cyclopentadienyl analogue.
Sandwich complexes are even known containing purely inorganic ligands.
What is one physical characteristic of a solid? Solids can be hard like a rock, soft like fur, a big rock like an asteroid, or small rocks like grains of sand. The key is that solids hold their shape and they don’t flow like a liquid. A rock will always look like a rock unless something happens to it. The same goes for a diamond. Solids can hold their shape because their molecules are tightly packed together.
You might ask, “Is baby power a solid? It’s soft and powdery.” Baby power is also a solid. It’s just a ground down piece of talc. Even when you grind a solid into powder, you will see tiny pieces of that solid under a microscope. Liquids will flow and fill up any shape of container. Solids like to hold their shape.
Atoms are still energetic, jiggle, and the electrons move in solids, but the atoms are locked in position. In the same way that a large solid holds its shape, the atoms inside of a solid are not allowed to move around too much. Atoms and molecules in liquids and gases are bouncing and floating around, free to move where they want. The molecules in a solid are stuck in a specific structure or arrangement of atoms. The atoms still vibrate and the electrons fly around in their orbitals, but the entire atom will not change its position.
Acid/Base chemistry began with the Arrhenius model of acids and bases. This model states molecules in water that release hydrogen ions (H+) are acids, while molecules in water that release hydroxide (OH-) are bases. This is not complete. The current common definition of an acid and a base is based upon how the substance releases or attracts hydrogen ions (H+). Acids release H+ ions that can turn neutral molecules into positively charged ions, while bases can attract H+ ions from neutral molecules to produce negatively charged ions. This definition allows for bases such as ammonia which does not contain a hydroxide ion.
In water solutions, acids affect water molecules, producing hydronium (H3O+) and bases also affect water molecules, producing hydroxide (OH-) ions. The relative strength of acids and bases is measured by their respective ion concentrations once dissolved. The product of the hydronium ion (H3O+) concentration in water times the hydroxide ion concentration equals 1*10 to the -14th power. When water is not the solvent, the product of the concentrations of the positive and negative ions produced by acids and bases also has a constant value, but the value is different for each solvent.
In water solutions, the pH is equal to the negative log of the hydronium ion (H3O+) concentration. The pOH is equal to the negative log of the hydroxide ion (OH-) concentration. For typical solutions, pH varies between 0 and 14, with 7 (the pH of water) as neutral. Each “step” below 7 is ten times more acidic (since it was derived from a power of ten). For concentrated solutions (> 1 M) of strong acids or bases, solutions can have pH below 0 or above 14 respectively. However, considering the water system at 25 °C, the pH plus pOH of a substance is equal to 14.
The notion of pH in fact depends on the considered solvent and can be extended to other non aqueous polar solvent systems with different autoprotolysis constant. In this case, the sum of pH and pOH is equal to the value of -log of this constant.
For acids and bases that fit the Arrhenius model, a reaction between them always produce water and a salt. Reactions between acids and metal always produce a salt and hydrogen gas.