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  2. Aufbau principle - Wikipedia

    en.wikipedia.org/wiki/Aufbau_principle

    Other authors write the subshells outside of the noble gas core in order of increasing n, or if equal, increasing n + l, such as Tl (Z = 81) [Xe]4f 14 5d 10 6s 2 6p 1. [5] They do so to emphasize that if this atom is ionized, electrons leave approximately in the order 6p, 6s, 5d, 4f, etc. On a related note, writing configurations in this way ...

  3. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    Within a galaxy such as the Milky Way, particles have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 10 5 to 10 9 atoms/m 3. [113] The Sun is believed to be inside the Local Bubble, so the density in the solar neighborhood is only about 10 3 atoms/m 3. [114]

  4. Molecular model - Wikipedia

    en.wikipedia.org/wiki/Molecular_model

    The plastic is white and can be painted to distinguish between O and N atoms. Hydrogen atoms are normally implicit and modelled by snipping off the spokes. A model of a typical protein with approximately 300 residues could take a month to build. It was common for laboratories to build a model for each protein solved.

  5. Lewis structure - Wikipedia

    en.wikipedia.org/wiki/Lewis_structure

    When Be is bonded with 2 other atoms, or when B and Al are bonded with 3 other atoms, they do not form full valence shells. Assume single bonds and use the actual bond number to calculate lone pairs. Expanded Octet (only occurs for elements in Groups 3-8) Bond calculation will provide too few bonds for the number of atoms in the molecule.

  6. Z-matrix (chemistry) - Wikipedia

    en.wikipedia.org/wiki/Z-matrix_(chemistry)

    In chemistry, the Z-matrix is a way to represent a system built of atoms.A Z-matrix is also known as an internal coordinate representation.It provides a description of each atom in a molecule in terms of its atomic number, bond length, bond angle, and dihedral angle, the so-called internal coordinates, [1] [2] although it is not always the case that a Z-matrix will give information regarding ...

  7. Chemical structure - Wikipedia

    en.wikipedia.org/wiki/Chemical_structure

    Theories of chemical structure were first developed by August Kekulé, Archibald Scott Couper, and Aleksandr Butlerov, among others, from about 1858. [4] These theories were first to state that chemical compounds are not a random cluster of atoms and functional groups, but rather had a definite order defined by the valency of the atoms composing the molecule, giving the molecules a three ...

  8. Chemical reaction - Wikipedia

    en.wikipedia.org/wiki/Chemical_reaction

    They consist of chemical or structural formulas of the reactants on the left and those of the products on the right. They are separated by an arrow (→) which indicates the direction and type of the reaction; the arrow is read as the word "yields". [10] The tip of the arrow points in the direction in which the reaction proceeds.

  9. Atoms in molecules - Wikipedia

    en.wikipedia.org/wiki/Atoms_in_molecules

    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.