atom

(noun)

The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.

Related Terms

Examples of atom in the following topics:

  • Stable Isotopes

    • Stable isotopes are atoms that are not radioactive, in other words, they are not going to lose neutrons and decay spontaneously.
    • Adding or subtracting neutrons from an atom does not change the elemental properties, but it can alter some of its features (like making it more radioactive).
    • While the number of neutrons in a particular atom can change, there is a certain threshold where the atom is given more neutrons that its nuclear force can hold.
    • During this time, the atom is deemed "unstable. " The atom will continue to lose neutrons until it become stable again.
    • This is a table that represents atom decay yielding various isotopes.

  • Nitrogenase and Nitrogen Fixation

    • To break one nitrogen atom away from another requires breaking all three of these chemical bonds.
    • Fixation processes free up the nitrogen atoms from their diatomic form (N2) to be used in other ways.
    • In most species, this heterometal complex has a central molybdenum atom.
    • However, in some species it is replaced by a vanadium or iron atom.

  • Crystallographic Analysis

    • Crystallographic analysis reveals the arrangement of atoms in solids that help build the three-dimensional model of molecules.
    • Crystallography is the scientific study of the arrangement of atoms in a solid.
    • Neutron crystallography is often used to help refine structures obtained by x-ray methods or to solve a specific bond; the methods are often viewed as complementary, as x-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly off many light isotopes, including hydrogen and deuterium.

  • Purine and Pyrimidine Synthesis

    • The carbon and nitrogen atoms of the purine ring, 5 and 4 respectively, come from multiple sources.
    • The amino acid glycine contributes all its carbon (2) and nitrogen (1) atoms, with additional nitrogen atoms coming from glutamine (2) and aspartic acid (1), and additional carbon atoms coming from formyl groups (2).
    • These are transferred from the coenzyme tetrahydrofolate as 10-formyltetrahydrofolate, along with a carbon atom from bicarbonate (1).
    • Formyl groups build carbon-2 and carbon-8 in the purine ring system, which are the ones acting as bridges between two nitrogen atoms.
    • The structure of purine is that of a cyclohexane(pyrimidine group) and cyclopentane(imidazole group) attached to one another; the Nitrogen atoms are at positions 1,3,7,9.

  • X-Ray Diffraction Analysis

    • X-ray diffraction (XRD) is a tool for characterizing the arrangement of atoms in crystals and the distances between crystal faces.
    • The method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences among various materials, especially minerals and alloys.
    • Further analysis involves structure refinement and quantitative phase using the general structure analysis system (GSAS), which ultimately leads to the identification of the amorphous or crystalline phase of a matter and helps construct its three dimensional atomic model .

  • Nitrogen Fixation Mechanism

    • Component I known as MoFe protein or nitrogenase contains 2 Mo atoms, 28 to 34 Fe atoms, and 26 to 28 acid-labile sulfides, also known as a iron-molybdenum cofactor (FeMoco).
    • This protein has four non-heme Fe atoms and four acid-labile sulfides (4Fe-4S).
    • Nitrogenase ultimately bonds each atom of nitrogen to three hydrogen atoms to form ammonia (NH3).

  • Growth Terminology

    • Autotrophs reduce carbon dioxide (CO2) by adding hydrogen atoms to it.
    • Most autotrophs use water as their reducing agent (to gain hydrogen atoms), but some can use other hydrogen compounds like hydrogen sulfide.

  • Syntrophy and Methanogenesis

    • Many methanogenic bacteria that live in close association with bacteria produce fermentation products such as fatty acids longer than two carbon atoms, alcohols longer than one carbon atom, and branched chain and aromatic fatty acids.

  • Scanned-Probe Microscopy

    • SPM covers several related technologies for imaging and measuring surfaces on a fine scale, down to the level of molecules and groups of atoms.
    • There are three common scanning probe techniques: atomic force microscopy (AFM) measures the interaction force between the tip and surface.

  • Nitrification

    • Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms):