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# Automic Radius Atomic radius is a measure of the size of an atom. It is typically defined as the distance from the center of the nucleus to the outermost electron. However, because the electron cloud does not have a definite boundary, atomic radius is difficult to measure precisely. The atomic ra...

# Automic Radius Atomic radius is a measure of the size of an atom. It is typically defined as the distance from the center of the nucleus to the outermost electron. However, because the electron cloud does not have a definite boundary, atomic radius is difficult to measure precisely. The atomic radius generally decreases across a period from left to right and increases down a group. ## Trends in Atomic Radius ### Across a Period As you move across a period from left to right, the atomic radius generally decreases. This is because the number of protons in the nucleus increases, which increases the effective nuclear charge experienced by the valence electrons. The increased nuclear charge pulls the valence electrons closer to the nucleus, resulting in a smaller atomic radius. ### Down a Group As you move down a group, the atomic radius generally increases. This is because the number of electron shells increases, which increases the distance between the valence electrons and the nucleus. The increased distance outweighs the effect of the increased nuclear charge, resulting in a larger atomic radius. ## Other Factors that Affect Atomic Radius ### Electron Configuration The electron configuration of an atom can also affect its atomic radius. For example, atoms with half-filled or completely filled electron shells tend to be more stable than atoms with partially filled electron shells. This increased stability can lead to a smaller atomic radius. ### Oxidation State The oxidation state of an atom can also affect its atomic radius. For example, when an atom loses electrons to form a positive ion, the remaining electrons are held more tightly by the nucleus, resulting in a smaller atomic radius. Conversely, when an atom gains electrons to form a negative ion, the added electrons increase the repulsion between the electrons, resulting in a larger atomic radius. ## Examples of Atomic Radius Here are some examples of atomic radii for different elements: | Element | Atomic Radius (pm) | | ------- | ------------------ | | H | 37 | | Li | 152 | | Na | 186 | | K | 227 | | Rb | 248 | | Cs | 265 | | Fr | 270 | | F | 71 | | Cl | 99 | | Br | 114 | | I | 133 | | At | 140 | ## Importance of Atomic Radius Atomic radius is an important property of atoms that affects their chemical behavior. For example, the size of an atom can affect its ability to form chemical bonds, its reactivity, and its physical properties such as melting point and boiling point. ## Premium Partner Vedantu **(bottom of page)**