Question

How does the reactivity of metals change from top to bottom on the periodic table?

Answer 1

Periodic table is basically an arrangement of all the known chemical elements on the basis of their atomic number. In the periodic table, there are certain trends like: trend of ionization enthalpy, atomic radius, and so on. Similarly, reactivity of the metals also changes from top to the bottom of the periodic table.

Complete answer:
In the periodic table, there are several trends that are followed on mostly the basis of their valence electrons such as: their metallic characteristics, electronegativity which is the ability of any atom to attract the bonding electrons present in the covalent bond, ionization enthalpy which is the amount of energy required to ionize an atom and so on.
Similarly, reactivity of the metal also changes from top to the bottom of the periodic table.
So, reactivity of the metals or non-metals depends upon their ability to lose their valence electrons, that is, their outermost electrons. If the metals are able to lose their valence electrons easily then the reactivity will be high and if they require more energy to lose their outermost electron, then their reactivity will be low. Also reactivity depends upon their atomic radius.
As we know, the metals at the top of the periodic table have small atomic radii as compared to the atomic radii of the metals at the bottom of the periodic table and that is because in the same group, nuclear charge remains same but as we move from top to the bottom of the table, addition of orbits takes place which increases the atomic radii, that is, the distance between the nucleus of the atom and the outermost electrons, so it becomes easier for the atom to lose their electrons and hence, increasing their reactivity. Since reactivity can be defined as the ability of the atom to lose their electrons to the chemical reaction.
For example: In group $II$, the reactivity of $Be$ is less as compared to $Ba$.

Note:
In the periodic table, almost every trend is inter-related. As we have seen above, the reactivity depends upon the atomic radii as well as their ability to lose their electrons for the chemical reactions.