Summary of Periodic Trends in Bonding Properties of Solids

Figure 6 summarizes the bonding properties of the elemental solids described above. As you can see, the bonding properties of these elemental solids follow particular trends across the periodic table. The less electronegative, metallic elements on the left of the table exhibit weak, nondirectional covalent bonding and no band gap. The more electronegative, nonmetallic elements on the right of the periodic table exhibit strong, directional covalent bonding and a large band gap. Semimetals, which occupy intermediate positions on the periodic table, have bonds of intermediate strength and directionality, and a small band gap. These periodic trends in bonding properties across a row of the periodic table derive from the electronegativities of the atoms. The relative electronegativites in turn are governed in part by the trends in the number of valence electrons that the atom holds.

Figure 6 This is a representation of the periodic table showing the trends in the bonding properties of solids from the left-hand side to the right-hand side.

These periodic trends in bonding properties are also related to the conductivity of the elements. The metals (on the left of the periodic table) tend to be good conductors of electricity, while the nonmetals (on the right of the periodic table) tend to be poor electrical conductors. The semimetals are typically classified as semiconductors, because they conduct electricity, but not as efficiently as the metals. Recall from the discussion of LEDs above that LEDs are semiconductor devices whose light-emitting properties are dependent on the nature of the bonding in the semiconductor. Hence, the next step in understanding how LEDs work is to describe the relationship between bonding (and the bands that form when the atoms are bonded together) and the conductivity properties of the elements.

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