Periodic Trends in Metallic-Nonmetallic Character

Metals, nonmetals and metalloids occupy visibly separate regions of the modern periodic table: metals cluster on the left, nonmetals on the right, and metalloids sit along the zig-zag line that divides the two (Fig. 7.1). Metals are characterised by good electrical conductivity and by forming compounds through the LOSS of valence electrons; nonmetals are characterised by poor electrical conductivity and by forming compounds through the GAIN of valence electrons into their own valence shell. Both of these tendencies can be explained directly using ionization enthalpy and electron gain enthalpy, already covered in sections 7.5.2.3 and 7.5.2.4. Since ionization enthalpy DECREASES down a group, the tendency to lose valence electrons increases correspondingly down a group — so METALLIC CHARACTER INCREASES DOWN A GROUP. Since ionization enthalpy INCREASES across a period, metallic character correspondingly DECREASES ACROSS A PERIOD. In the opposite direction, since electron gain enthalpy becomes progressively MORE NEGATIVE …