Thus, as you move down the periodic table, both the size of the nucleus and the number of shells grows, increasing the total radius.įor example the atomic radius of Lithium is 152 picometers, but if we progress down to caesium, its atomic radius is 262 picometers. The size of the nucleus also increases as you move down the group. This increases the atomic radius as the electrons in the outermost shell are further away from the nucleus. ‍ Atomic Radius Trends on the Periodic TableĪs we progress down a group in the periodic table, the number of electrons increases, and so does the number of shells that those electrons are organized into. The atomic radius is measured in picometers, which is one trillionth of a meter or 1x10-12. Because the boundaries where the electron shells end on an atom can be a bit unclear, the actual definition of atomic radius is one-half the distance between the nuclei of two identical bonded atoms. Atomic radius is the distance from the atom’s nucleus to the outermost electron orbital, and a lot of trends in the periodic table rely on this property due to its relationship to other atomic properties such as nuclear charge and shielding. The atomic radius of a particular element is an important characteristic as it helps us to understand many properties of atoms and how they react. Helium is in the top period and the farthest right group, which follows the patterns of atomic radius on the periodic table. Helium has the smallest atomic radius at 31 picometers.

Which element has the smallest atomic radius? This means the electrons are pulled more closely to the nucleus, reducing the size of the atomic radius. Thus, as the nuclear charge increases across a period, the protons in the nucleus can attract the higher number of electrons more closely due to the attraction of the positive protons to the negative electrons. Why does the atomic radius decrease across a period?Īcross a period, the number of electron shells remains the same, while the number of electrons increases. Why does the atomic radius increase as you progress down a group?Īs we progress down a group in the periodic table, the number of electrons increases, and so does the number of shells that those electrons are organized into. The atomic radius is calculated by measuring the distance between the nuclei of two identical atoms bonded together.

Elements in the same period have the same number of electron shells, while elements in the same group have the same number of valence electrons. Periods run across the table horizontally, while groups are the vertical groupings. Elements in the periodic table are organized into periods and groups. Refresher: Atoms consist of a nucleus with positively charged protons and neutral neutrons surrounded by shells of electrons.

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