The biggest atom, in terms of atomic size, is Francium (Fr).
According to the provided reference, Francium has the largest atomic size on the periodic table.
While atomic mass and atomic size are related, they are not the same thing. Atomic mass refers to the total mass of protons, neutrons, and electrons in an atom, whereas atomic size (atomic radius) refers to the distance from the nucleus to the outermost electron. The size of an atom is primarily determined by:
- Number of electron shells: As you move down a group in the periodic table, atoms gain more electron shells, thus increasing their size.
- Effective nuclear charge: This is the net positive charge experienced by valence electrons. A higher effective nuclear charge pulls the electrons closer to the nucleus, decreasing the atomic size. As you move across a period in the periodic table, the effective nuclear charge generally increases, leading to a decrease in atomic size.
Because Francium is located in the bottom left of the periodic table (Group 1, Period 7), it possesses the most electron shells and experiences relatively weak effective nuclear charge compared to elements in the same period. This combination results in the largest atomic size. Helium (He), conversely, is at the top right, giving it the smallest atomic size.
| Element | Atomic Number | Relative Atomic Size |
|---|---|---|
| Francium | 87 | Largest |
| Helium | 2 | Smallest |
