This results in a greater repulsion among the

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This results in a greater repulsion among the electrons and a decrease in Z eff . This causes the valence electrons to be farther from the nucleus. An anion is always larger than the atom from which it is derived.
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FIGURE 6.33 The radius for a cation is smaller than the parent atom (Al), due to the lost electrons; the radius for an anion is larger than the parent (S), due to the gained electrons.
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ISOELECTRONIC Atoms and ions that have the same electron configuration are said to be isoelectronic . Examples of isoelectronic species: N 3– , O 2– , F , Ne, Na + , Mg 2+ , and Al 3+ (1 s 2 2 s 2 2 p 6 ). P 3– , S 2– , Cl , Ar, K + , Ca 2+ , and Sc 3+ ([Ne]3 s 2 3 p 6 ). For atoms or ions that are isoelectronic, the number of protons determines the size. The greater the nuclear charge, the smaller the radius in a series of isoelectronic ions and atoms.
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IONIZATION ENERGY The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy (IE 1 ) . X( g ) X + ( g ) + e IE 1 The energy required to remove the second most loosely bound electron is called the second ionization energy (IE 2 ) . X + ( g ) X 2+ ( g ) + e IE 2 The energy required to remove the third electron is the third ionization energy, and so on.
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VARIATIONS IN IONIZATION ENERGIES Energy is always required to remove electrons from atoms or ions, so ionization processes are endothermic and IE values are always positive. As size (atomic radius) increases, the ionization energy decreases. First ionization energies: Decrease down a group Increase across a period There are some deviations from this trend.
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FIGURE 6.34 The first ionization energy of the elements in the first five periods are plotted against their atomic number.
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