Chapter 7 - Periodic Properties of the Elements

Chapter 7 - Periodic Properties of the Elements - Chapter...

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Chapter 7— Periodic Properties of the Elements 7.1 Development of the Periodic Table Many elements have been known since ancient times. Mercury and sulfur for example were made by the Greeks by heating the mineral cinnabar. The idea that matter is composed of the elements “earth, air, fire and water” is equally ancient. As a matter of fact they had a systematized logic explaining the nature of each substance – and it was put in tabular form. It is deep within the human soul to want to be able to explain, and therefore predict the nature of the world around us. After Antoine Lavoisier in the 1700’s, chemistry became rigorous, chemists measured carefully and consistently. By the early 1860’s some ninety elements were known. Certain similarities had been observed, for example (Magnesium, Calcium & Strontium) and (Chlorine, Bromine & Iodine) were called triads. However it wasn’t until the mid 1850’s that a Russian Chemist, Dmitri Mendeleev sorted out the chemical in a systematic way. His biggest triumph was to insist that when a hole existed (or an element didn’t fit) into his table that it was because that element had yet to be discovered. Three of these elements were Eka-Boron (Scandium), Eka- Aluminum (Gallium), Eka-Silicon (Germanium). He boldly predicted their chemical and physical properties. There was a mad rush to find them, and to either prove or disprove Mendeleev’s theories. Within years these elements were discovered and Lo and Behold Mendeleev had been absolutely correct! His chemical insights and his bold challenge to his contemporary scientists insured his place in history.
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Since Mendeleev’s time there have been many revisions p2 of the periodic table. The transition metals were recognized. In the mid 1950’s Glen Seaborg, a physicist, not a chemist, noticed that the trans-uranium elements did not really belong with the transition metals in the periodic table. He created a separate section that he and now we call the Lanthanides and Actinides. This brought into clear focus that the periodic table was laid out in order of electron filling that we have learned in Chapter 6. This clearly tells us that the chemical and physical properties of an element are determined by the electron configuration of that element. Now we will attempt to make some sense of this legacy of both chemical and physical thought. 7.2 Effective Nuclear Charge Effective Nuclear Charge (Z eff ): The nuclear charge felt by the valence electrons. Z eff = Z-S Z eff = nuclear charge (Z) – shielding by core electrons (S) Effective Nuclear Charge for the 3 rd period the core noble gas is ____ which has ____ electrons Elmt
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Chapter 7 - Periodic Properties of the Elements - Chapter...

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