Most Reactive Metal on the Periodic Table

Reactivity and the Metal Activity Series

Caesium Cs, chemical element. 3D rendering isolated on black background
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The most reactive metal on the periodic table is francium. However, francium is a man-made element and only minute quantities have been produced, so for all practical purposes, the most reactive metal is cesium. Cesium reacts explosively with water, though it is predicted francium would react even more vigorously.

Using the Metal Activity Series To Predict Reactivity

You can use the metal activity series to predict which metal will be the most reactive and to compare reactivity of different metals. The activity series is a chart that lists elements according to how readily the metals displace H2 in reactions.

If you don't have the chart of the activity series handy, you can also use trends in the periodic table to predict the reactivity of a metal or nonmetal. The most reactive metals belong to the alkali metals element group. Reactivity increases as you move down the alkali metals group. The increase in reactivity correlates to a decrease in electronegativity (increase in electropositivity). So, just by looking at the periodic table, you can predict lithium will be less reactive than sodium and francium will be more reactive than cesium and all of the other elements listed above it in the element group.

What Determines Reactivity?

Reactivity is a measure of how likely a chemical species is to participate in a chemical reaction to form chemical bonds. An element that is highly electronegative, such as fluorine, has an extremely high attraction for bonding electrons. Elements at the opposite end of the spectrum, such as highly reactive metals cesium and francium, readily form bonds with electronegative atoms. As you move down a column or group of the periodic table, the size of the atomic radius increases. For the metals, this means the outermost electrons becomes further away from the positively-charged nucleus. These electrons are easier to remove, so the atoms readily form chemical bonds. In other words, as you increase the size of atoms of metals in a group, their reactivity also increases.