Here's why:
* Atomic number: Chromium has an atomic number of 24, while Copper has an atomic number of 29. This means Copper has more protons and electrons than Chromium.
* Electron configuration: The extra electrons in Copper fill a higher energy level (3d shell) compared to Chromium. This increased electron shielding from the inner shells causes the outermost electrons in Copper to experience a weaker attraction to the nucleus, leading to a larger atomic radius.
* Trends in the periodic table: Going across a period in the periodic table, atomic radius generally decreases due to increased nuclear charge and a stronger pull on the electrons. This trend is further amplified by the addition of electrons to the same energy level in Copper.
In summary: Copper has a larger atomic radius than Chromium due to the greater number of electrons and the higher energy level of its outermost electrons.
