Relating Metallic Reactivity to Atomic Structure Relating Metallic Reactivity to Atomic Structure Let's consider how metals react.
Metals react by losing electrons.
The electrons are being held more tightly as you go across a period. It becomes more and more difficult to lose electrons and consequently the reactivity of the metals decreases as you go from left to right across the periodic table. Consequently the dominant factor is that we have more and more energy levels and the electrons are further and further away from the nucleus. Thus it is easier for those electrons to come off. Those are the reasons for the pattern of reactivity that is seen for the metals.