DAVID PARKER / SCIENCE PHOTO LIBRARY DAVID PARKER / SCIENCE PHOTO LIBRARY
Artwork showing the electron clouds, or orbitals, of atoms of hydrogen (top), carbon (top left), silicon (top right), iron (centre left), silver (centre right), & europium (bottom). As the number of electrons increases, additional orbitals are filled according to a regular pattern of spherical 's' orbitals (white to blue), dumbbell-shaped 'p' orbitals (orange), 'd' orbitals (yellow-green) shaped like crossed dumbbells, & 'f' orbitals (purple). The extent to which an element's electrons fill these orbitals determines its chemical characteristics.
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