The largest atom is generally considered to be cesium (Cs), which is located in Group 1 of the periodic table. Cesium has an atomic number of 55 and features the largest atomic radius among the elements.
This size can be attributed to its position on the periodic table. As you move down a group, each successive element has an additional electron shell. For cesium, this means it has six electron shells, which significantly increases its atomic size compared to lighter elements like hydrogen or lithium that have fewer shells.
Furthermore, the outermost electrons of cesium are located much farther from the nucleus than those of smaller atoms, contributing to the atom’s larger size. This increased distance reduces the effective nuclear charge felt by the outermost electrons, allowing them to spread out more and resulting in a larger atomic radius.