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In quantum chemistry, the quantum theory of atoms in molecules (QTAIM), sometimes referred to as atoms in molecules (AIM), is a model of molecular and condensed matter electronic systems (such as crystals) in which the principal objects of molecular structure - atoms and bonds - are natural expressions of a system's observable electron density distribution function.
Coordination numbers of 8 to 12 are commonly observed for f-block elements. For example, with bidentate nitrate ions as ligands, Ce IV and Th IV form the 12-coordinate ions [Ce(NO 3) 6] 2− (ceric ammonium nitrate) and [Th(NO 3) 6] 2−. When the surrounding ligands are much smaller than the central atom, even higher coordination numbers may ...
This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit, each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg. [65]
Note: All measurements given are in picometers (pm). For more recent data on covalent radii see Covalent radius.Just as atomic units are given in terms of the atomic mass unit (approximately the proton mass), the physically appropriate unit of length here is the Bohr radius, which is the radius of a hydrogen atom.
The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride, chlorine has a valence of 1.
In type theory, an object of type 0 can be called an urelement; hence the name "atom". Adding urelements to the system New Foundations (NF) to produce NFU has surprising consequences. In particular, Jensen proved [ 5 ] the consistency of NFU relative to Peano arithmetic ; meanwhile, the consistency of NF relative to anything remains an open ...
The atomic ratio is a measure of the ratio of atoms of one kind (i) to another kind (j). A closely related concept is the atomic percent (or at.%), which gives the percentage of one kind of atom relative to the total number of atoms. [1]
A few mixed halides and hydrohalides are known, but are mostly unstable; examples include NClF 2, NCl 2 F, NBrF 2, NF 2 H, NFH 2, NCl 2 H, and NClH 2. [ 61 ] Nitrogen trifluoride (NF 3 , first prepared in 1928) is a colourless and odourless gas that is thermodynamically stable, and most readily produced by the electrolysis of molten ammonium ...