Aluminum oxide Lewis structure

Lewis Structures of Atoms

• The chemical symbol for the atom is surrounded by a number of dots corresponding to the number of valence electrons.

Lewis Structures for Ions of 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 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

Lithium fluoride, LiF

• Lithium atom loses one electron to form the cation Li+
• Fluorine atom gains one electron to form the anion F-
• Lithium fluoride compound can be represented asLi+ OR

Lithium oxide, Li2O

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.

hydrogen fluoride, HF

ammonia, NH3

oxygen molecule, O2

• Each oxygen will share 2 of its valence electrons in order to form 2 bonding pairs of electrons (a double covalent bond) so that each oxygen will have a share in 8 valence electrons (electronic configuration of neon).
• Lewis Structure (electron dot diagram) for the oxygen molecule OR

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