Logic Masters Deutschland e.V.

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Puzzle link: Play on SudokuPad.

Rules: Normal Sudoku rules apply. A circle defines an “atom” and grey lines “valence orbitals”. The number of “valence electrons” of an atom, not necessarily written in the circle, is given by the sum of all digits on diagonally or orthogonally adjacent cells connected to that atom with valence orbitals. Each atom is either a “main-group atom” with eight valence electrons or a “transition-metal atom” with 18 valence electrons. Two transition-metal atoms must not be directly connected through a valence orbital; there always has to be at least one main-group atom in between.

Background (not required for solving the puzzle): This puzzle is based on the octet rule (also known as the eight-electron rule) of chemistry, according to which atoms of the main group elements strive to adopt a configuration of eight outer electrons (valence electrons), the so-called noble gas configuration, as this is particularly stable. For transition metals, the 18-electron rule applies equivalently. And metal coordination complexes with several transition metal atoms usually indeed contain another element as a “bridge” between them. However, there are exceptions to all three rules in reality.