Chemists write the Lewis structure of the hydroxide ion as H-O with an additional set of 3 electron pairs surrounding the oxygen, one pair at the 12 o'clock position, a second pair at the 3 o'clock position and the final pair at the 6 o'clock position. The entire ion is then surrounded by brackets with a negative sign at the top right, representing the overall ionic charge.
Lewis structures involve choosing the central atom and writing its symbol. The rules state it should have the lowest electronegativity. Electronegativity decreases on the periodic table from top to bottom and from right to left. Other atoms in the ion or compound connect with a dash to represent a single bond; however, it is sometimes necessary to change to double or triple bonds to complete the structure.
Students generally do not draw Lewis structures for elements beyond period 4 which require additional electrons to fill their outer shell, so they are able to use the octet rule. It states that with the exception of hydrogen and helium, atoms with 8 electrons in the outer shell are stable.
The structure represents the number of electrons each atom donates as dots around it. Some atoms do not provide enough electrons to satisfy the octet rule, requiring double or triple bonds. Each bond represents two electrons.
Once electrons are in their place, the scientist draws brackets around the entire structure. A superscript sign at the right of the last bracket represents any charge on an ion.