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Date: 21-7-2020
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Date: 2-2-2018
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Date: 24-6-2019
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The Periodic Table
When Dimitri Mendeleev constructed the periodic table in 1869, he knew nothing of electronic configurations or even of atomic numbers. He grouped elements in order of increasing atomic mass (with a few exceptions, e. g., Ni and Co) arranged in columns of elements with similar chemical properties. We now see that this similarity is due to similar electronic configurations. Thus all alkali metals (Group I) have the valence electron configuration ns1, all alkaline earth metals (Group II) have the configuration ns2, all halogens (Group VII) all ns2np5, etc.
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ما أبرز التغيرات التي تحدث عند الرجال عندما يصبحون آباءً؟
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حقائق مثيرة للاهتمام حول الأرض
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قسم الشؤون الفكرية يصدر العدد 53 من مجلة عطاء الشباب
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