01:160:161 Lecture Notes - Lecture 4: Electron Shell, Atomic Number, Nonmetal

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Mendelev arranged the elements in order of increasing atomic masses (atomic number concept was not known) The current periodic table arranges the elements in groups (columns) and periods (rows) in order of increasing atomic number (number of protons) The periodic table can then be divided into blocks depending on the last subshell that is occupied by the electrons according to the aufbau principle. The group number (except for he) indicates the number of electrons in the valence shell of that element for the main group elements 1a-7a (representative elements). Periodicity of some physical properties: variation in atomic size (r) The further away is the electron from the nucleus. n2 increases faster than zeff . Across a period size decreases. r n2/zeff n = constant across a period. There is a stronger attraction between the protons in the nucleus and the outermost e . For b-group elements ( transition elements ) electrons enter an inner electron shell.

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