In the mathematical field of order theory, an element a of a partially ordered set with least element 0 is an atom if 0 < a and there is no x such that...

Atomic theory is the scientific theory that matter is composed of particles called atoms. The definition of the word "atom" has changed over the years...

electrons. Atom(s) may also refer to: Atom (time), a medieval unit of time Atom (measure theory), a minimal measurable set Atom (order theory) Atomic formula...

measure theory, an atom is a measurable set which has positive measure and contains no set of smaller positive measures. A measure which has no atoms is called...

the hydrogen atom, compared to the valence shell model. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader...

Era" Atomic scale, distances comparable to the dimensions of an atom Atom (order theory), in mathematics Atomic (cocktail), a champagne cocktail Atomic...

century) and others, developed distinctive theories of atomism, for example, involving momentary (instantaneous) atoms (kalapas) that flash in and out of existence...

Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically...

orthogonality in a component-based system Atomicity, in order theory; see Atom (order theory) Atom (disambiguation) This disambiguation page lists articles...

A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral hydrogen atom contains a nucleus of a single positively charged proton...

composed of atoms. The structure of the atom was discussed, and by the end of the century the leading model: 175  was the vortex theory of the atom, proposed...

century. In molecular orbital theory, electrons in a molecule are not assigned to individual chemical bonds between atoms, but are treated as moving under...

An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example...

number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm theory after its two main developers, Ronald Gillespie and...

atoms. Aczel's anti-foundation axiom implies that there is a unique Quine atom. Other non-well-founded theories may admit many distinct Quine atoms;...

of the dissociated atoms combine to give individual chemical bonds when a molecule is formed. In contrast, molecular orbital theory has orbitals that cover...

Atomism or social atomism is a sociological theory arising from the scientific notion atomic theory, coined by the ancient Greek philosopher Democritus...

In first-order logic, a first-order theory is given by a set of axioms in some language. This entry lists some of the more common examples used in model...

hyperfine splitting in the hydrogen atom. Despite the simpler notation, perturbation theory applied to quantum field theory still easily gets out of hand....

essence, means that the atoms share "valence", such as is discussed in valence bond theory. In the molecule H 2, the hydrogen atoms share the two electrons...

phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids...

chemistry, bond order is a formal measure of the multiplicity of a covalent bond between two atoms. As introduced by Linus Pauling, bond order is defined as...

of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic...

of dark energy, called phantom energy theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn...

hydrogen atom, the quantum harmonic oscillator and the particle in a box, are too idealized to adequately describe most systems. Using perturbation theory, we...

chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell...

Energeticism – a theory that attempted to reinterpret all chemistry in terms of energy, rejecting the concept of atoms. Caloric theory – the theory that a self-repelling...

of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s2...

1913 by Danish physicist Niels Bohr in the Bohr theory of the atom. The modern quantum mechanical theory giving an explanation of these energy levels in...

state) of many-body systems, in particular atoms, molecules, and the condensed phases. Using this theory, the properties of a many-electron system can...