Question

An increase in what, across the periodic table, explains why elements go from metals to metalloids and then to nonmetals?

Answer 1

electrons

The increase in electrons across the periodic table explains why elements go from metals to metalloids and then to nonmetals from left to right across the table. Look at period 2 in Figure below as an example. Lithium  Li  is a metal, boron  B  a metalloid, and fluorine  F  and neon  Ne  are nonmetals. The inner energy level is full for all four elements. This level has just one orbital and can hold a maximum of two electrons. The outer energy level is a different story. This level has four orbitals and can hold a maximum of eight electrons. Lithium has just one electron in this level, boron has three, fluorine has seven, and neon has eight.