ROGER HARRIS / SCIENCE PHOTO LIBRARY ROGER HARRIS / SCIENCE PHOTO LIBRARY
Zinc atom. Diagram of an atom of the element zinc, showing the outer electron orbitals. Zinc is the 30th element, and has 30 protons (red) in its nucleus (not seen), which means it has 30 electrons also. Each orbital can hold a maximum of two. Orbitals are filled from the lowest energy (nearest the nucleus) first. The inner orbitals have been removed for clarity here, but include the inner 1s orbital, a 2s orbital, three 2p orbitals, and a 3s and three 3p orbitals. Visible here, at a higher energy, is a spherical 4s orbital (green), and then five 3d orbitals. The 3d orbitals are arranged as three X-shaped orbitals arranged in the x, y and z plane (red, green and yellow), one X-shaped orbital in the x plane but at 45 degrees to the other (blue), and one two-lobed orbital in the z plane, with a small ring around the nucleus (purple). For clarity, solid lines show the paths of the electrons. In reality, electrons can be found anywhere, and the shape of each orbital is based only on where it is most likely to be found.
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