Click to edit Master subtitle styleChapter 9 – Periodic Table and Atomic Properties So, the periodic table was first developed by Mendeleev and Meyer on the basis of similar chemical and physical properties exhibited by certain elements. We now know that elements in the same group of the periodic table have the same number of electrons in their valence orbitals(highest associated principal quantum number), hence similarities in properties are due to similarities in valence electronic structure. Many properties of atoms arise due to the average distance of outer electrons from the nucleus, and by extension to the effective nuclear charge (Zeff)experienced by these outer electrons. The Zeff felt by an outer electron is the actual nuclear charge less the screening effect of all other electrons in the atom. The core electrons(those with an n value less than the valence electrons) are able to shield the outer (valence) electrons from the full charge (Z) of the nucleus, whereas electrons in the same shell do not shield each other very well. As a result, the Zeff for valence electrons increases as we go left to right across a period in the periodic table (adding extra protons to the nucleus and
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