Sept_17 - The Periodic Table Elements in the same group of...

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The Periodic Table Elements in the same group of the periodic table have similar electron configurations. Electrons in the outermost electron shell are called valence electrons . For example, consider Group 17 (the halogens): – F [He] 2s 2 2p 5 – Cl [Ne] 3s 2 3p 5 – Br [Ar] 4s 2 3d 10 4p 5 – I [Kr] 5s 2 4d 10 5p 5 – At [Xe] 6s 2 4f 14 5d 10 6p 5 All group 17 elements have 7 valence electrons (ns 2 np 5 ) The d and f electrons are low in energy and do not strongly influence the chemistry of Br, I, At
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Periodic Trends trends in the properties of the elements generally reflect how strongly valence electrons are attracted to the nucleus the attraction is Coulombic F q + q - r 2 distance from the nucleus, i.e, which shell the valence electrons are in (r) the effective net positive charge attracting the valence electrons (q + ) q + is approximately equal to the number of valence electrons
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Sizes of Atoms and Ions Atomic radius is difficult to define – the probability of
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