Atomic radius/radii predicting relative sizes

The electron configuration or orbital diagram of an atom of an element can be deduced from its position in the periodic table. Beyond that, position in the table can be used to predict (Section 6.8) the relative sizes of atoms and ions (atomic radius, ionic radius) and the relative tendencies of atoms to give up or acquire electrons (ionization energy, electronegativity). 

Knowing the information just presented, we can now predict the relative size of the atoms and ions presented. Because they all have 18 electrons we can look at the number of protons present as well. The ion with the greatest number of protons, Ca, will have the smallest radius because it has the greatest nuclear pull on the 18 electrons. Sulfur, with just 16 protons, will have the least nuclear attraction for the 18 electrons that it has. This helps explain why non-metal atoms are smaller than their respective ions. Just the same, it also explains why metal atoms are larger than their respective ions. 

Ionic Size vs. Atomic Size The ionic radius is an estimate of the size of an ion in a crystalline ionic compound. You can picture it as one ion s portion of the distance between the nuclei of neighboring ions in the solid (Figure 8.21). From the relation between effective nuclear charge and atomic size, we can predict the size of an ion relative to its parent atom ... 

The relative size of sodium and potassium ions is an example of a periodic property one that is predictable based on an element s position within the periodic table. In this chapter, we examine several periodic properties of elements, including atomic radius, ionization energy, and electron affinity. We will see that these properties, as well as the overall arrangement of the periodic table, are explained by quantum-mechanical theory, which we examined in Chapter 7. The arrangement of elements in the periodic table— originally based on similarities in the properties of the elements— reflects how electrons fill quantum-mechanical orbitals. 

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