How does the reactivity of metals generally change across a period?

As you move across a period in the periodic table from left to right, the reactivity of metals generally decreases. This trend is primarily due to the increase in nuclear charge as more protons are added to the nucleus. While the number of electrons increases as well, these additional electrons are added to the same energy level and do not effectively shield the increased positive charge of the nucleus.

As a result, the attraction between the positively charged nucleus and the outermost electrons becomes stronger. This greater effective nuclear charge makes it more difficult for metals to lose their outer electrons, which is a key factor in metallic reactivity. Therefore, metals in the alkaline earth metals category (like magnesium) and transition metals are less reactive compared to those in the alkali metals group found on the far left.

This decrease in reactivity reflects the trend in metallic characteristics, where metals on the left side of the periodic table readily lose electrons while those on the right are more tightly bound due to their larger nuclear charge.