Lewis Dot Rules:
Lewis Structures of Atoms
* The chemical symbol for the atom is surrounded by a number of dots corresponding to the number
of valence electrons. Note Bold numbers is the IUPAC group numbers.
Lewis Structures for Ions of Pure Elements
* The chemical symbol for the element is surrounded by the number of valence electrons present in
the ion.
* The whole structure is then placed within square brackets, with a superscript to indicate the charge
on the ion.
* Atoms will gain or lose electrons in order to achieve a stable, Noble Gas (Group VIII or 18),
electronic configuration.
* Negative ions (anions) are formed when an atom gains electrons.
* Positive ions (cations) are formed when an atom loses electrons.
Lewis Structures for Ionic Compounds
* The overall charge on the compound must equal zero, that is, the number of electrons lost by one
atom must equal the number of electrons gained by the other atom.
* The Lewis Structure (electron dot diagram) of each ion is used to construct the Lewis Structure
(electron dot diagram) for the ionic compound.
Examples
Lewis Structures for Covalent Compounds
* In a covalent compound, electrons are shared between atoms to form a covalent bond in order that
each atom in the compound has a share in the number of electrons required to provide a stable, Noble
Gas, electronic configuration.
* Electrons in the Lewis Structure (electron dot diagram) are paired to show the bonding pair of
electrons.
* Often the shared pair of electrons forming the covalent bond is circled
* Sometimes the bond itself is shown (-), these structures can be referred to as valence structures.
Questions From Lewis Dots for previous Regents Tests
Example:
1. #38 8/2009 Which Lewis electron-dot diagram represents calcium oxide?
Ans: 4
2. #64 6/2009 In the space in your answer booklet, draw a Lewis electron-dot diagram for an atom of
sulfur-33.
Ans:
3. #51 1/2009 In the box in your answer
booklet, draw a Lewis electron-dot diagram for an atom of boron.
Ans: The lewis structure of B or Boron would have three small dots posing as electrons. These
dots can be placed anywhere around the B symbol. Example of some acceptable answers are shown
below, the un-pairing of electrons is typically the more common Lewis dot placement as shown on the
left two examples:
4. #80 8/2008 In the space in your answer booklet, draw a Lewis electron-dot diagram for one of
the positive ions lost by the body as a person perspires.
The positive ions the body loses are sodium Na+ and potassium K+ positive ions (cations) when a
+
person perspires, the Lewis electron-dot diagram for the sodium ion is [Na] for the the potassium ion
+
[K] .
5. 6/2008 No questions
6. In the space in your answer booklet, draw a Lewis electron-dot diagram for the proposed
undiscovered atom of Uut that has an atomic number of 113.
Ans: If the atom is found it will be in column 13 giving it 3 valence electrons so the possible
Lewis dot diagrams are:.
7. #55, 56 and 57 1/2009