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  2. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper.

  3. Electron shell - Wikipedia

    en.wikipedia.org/wiki/Electron_shell

    In chemistry and atomic physics, an electron shell may be thought of as an orbit that electrons follow around an atom's nucleus.The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or "L shell"), then the "3 shell" (or "M shell"), and so on further and further from the nucleus.

  4. Octet rule - Wikipedia

    en.wikipedia.org/wiki/Octet_rule

    The bonding in carbon dioxide (CO 2): all atoms are surrounded by 8 electrons, fulfilling the octet rule.. The octet rule is a 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, giving it the same electronic configuration as a noble gas.

  5. Periodic table - Wikipedia

    en.wikipedia.org/wiki/Periodic_table

    Boron (1s 2 2s 2 2p 1) puts its new electron in a 2p orbital; carbon (1s 2 2s 2 2p 2) fills a second 2p orbital; and with nitrogen (1s 2 2s 2 2p 3) all three 2p orbitals become singly occupied. This is consistent with Hund's rule , which states that atoms usually prefer to singly occupy each orbital of the same type before filling them with the ...

  6. Oxidation state - Wikipedia

    en.wikipedia.org/wiki/Oxidation_state

    In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms are fully ionic.It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound.

  7. Atomic, molecular, and optical physics - Wikipedia

    en.wikipedia.org/wiki/Atomic,_molecular,_and...

    One attempt to explain hydrogen spectral lines was the Bohr atom model. [ 13 ] Experiments including electromagnetic radiation and matter - such as the photoelectric effect , Compton effect , and spectra of sunlight the due to the unknown element of Helium , the limitation of the Bohr model to Hydrogen, and numerous other reasons, lead to an ...

  8. Half-life - Wikipedia

    en.wikipedia.org/wiki/Half-life

    It varies depending on the atom type and isotope, and is usually determined experimentally. See List of nuclides. The current flowing through an RC circuit or RL circuit decays with a half-life of ln(2)RC or ln(2)L/R, respectively. For this example the term half time tends to be used rather than "half-life", but they mean the same thing.

  9. Atomic number - Wikipedia

    en.wikipedia.org/wiki/Atomic_number

    For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (n p) or the number of protons found in the nucleus 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 number is also equal to the number of electrons.