Francium (Fr) has the largest atomic radius.
Francium, an alkali metal with an atomic number of 87, holds the distinction of having the largest atomic radius among all elements in the periodic table. This is due to the factors influencing atomic size, including the number of electron shells and the effective nuclear charge.
Factors Influencing Atomic Radius:
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Number of Electron Shells: As you move down a group in the periodic table, elements gain additional electron shells. These added shells increase the distance between the nucleus and the outermost electrons, resulting in a larger atomic radius. Francium, being at the bottom of Group 1 (alkali metals), possesses the most electron shells.
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Effective Nuclear Charge: The effective nuclear charge is the net positive charge experienced by an electron in a polyelectronic atom. While the nuclear charge (number of protons) increases across a period, the shielding effect of inner electrons reduces the effective nuclear charge experienced by the outer electrons. This shielding effect is more prominent down a group. Although Francium has a high nuclear charge, it is significantly shielded by its inner electrons, leading to a relatively weak attraction between the nucleus and the outermost electron. This weak attraction allows the electron cloud to expand, further contributing to its large atomic radius.
Periodic Trends:
Atomic radius generally:
- Increases as you move down a group (due to increased electron shells).
- Decreases as you move across a period (due to increased effective nuclear charge).
Francium resides in the lower left corner of the periodic table, where elements exhibit the largest atomic radii. Elements like Cesium (Cs) are also large but are smaller than Francium.
