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Sulfur (S) has 16 electrons, so its electron configuration is 1s²2s²2p⁶3s²3p⁴. In noble gas notation, this can be written as [Ne]3s²3p⁴.
This electron configuration has 12 electrons total, which corresponds to Magnesium (Mg). The configuration shows the first three energy levels are filled according to the aufbau principle.
Filling order follows how electrons actually fill orbitals (aufbau principle), while energy order lists subshells by increasing energy. For example, 4s fills before 3d, so filling order is [Ar]4s²3d⁵ while energy order is [Ar]3d⁵4s².
Elements like Copper (Cu), Silver (Ag), Gold (Au), Chromium (Cr), and others have electron configurations that don't follow the expected pattern due to stability gained from half-filled or fully-filled d subshells.
Start with the noble gas that comes before your element in brackets, then continue with the remaining electrons. For example, Sodium (Na) is [Ne]3s¹ instead of writing the full 1s²2s²2p⁶3s¹.
Valence electrons are the outermost electrons that participate in bonding. For main group elements, count electrons in the highest energy level (s and p orbitals). For transition metals, include both s and d electrons of the highest energy levels.
Electron configuration determines an element's chemical properties, bonding behavior, magnetic properties, and position in the periodic table. It explains trends like atomic size, ionization energy, and electronegativity.
Each s orbital holds 2 electrons, p orbitals hold 6 electrons total (3 orbitals × 2), d orbitals hold 10 electrons total (5 orbitals × 2), and f orbitals hold 14 electrons total (7 orbitals × 2).