LewisDiagrams - LEWIS DIAGRAMS by DR STEPHEN THOMPSON MR...

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LEWIS DIAGRAMS The contents of this module were developed under grant award # P116B-001338 from the Fund for the Improve- ment of Postsecondary Education (FIPSE), United States Department of Education. However, those contents do not necessarily represent the policy of FIPSE and the Department of Education, and you should not assume endorsement by the Federal government. by DR. STEPHEN THOMPSON MR. JOE STALEY �� �� �� �� �� �� �� �� �� ��
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LEWIS DIAGRAMS CONTENTS 2 Lewis Diagrams For Covalent Bonding 3 Lewis Diagrams For Covalent Bonding 4 Forming Lewis Diagrams 5 Resonance 6 Beyond The Steps 7 Beyond The Steps 7 Orbitals
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LEWIS DIAGRAMS FOR COVALENT BONDING In the figure below, the elements of the first three periods are shown with their valence electrons surrounding their symbols. It is only the valence electrons which may become involved in chemical bonding, because the inner electron shells are held too tightly to the atom to be either shared of given up in chemical bonding, although you can blast them off with X-rays. �� �� �� �� �� �� �� �� �� �� Electronegativity �� �� �� �� �� �� If we consider just the nonmetals, as shown below, the electronegativity differences between the ele- ments is fairly small. For this reason a particular kind of bonding, called covalent bonding, occurs between the atoms. Because of the small electronegativity differences, none of the atoms in a covalent molecule pulls any electrons entirely away from any of the other atoms, but rather the atoms share some or all of the valence electrons. In covalent bonding electrons are always shared in pairs. In this example the pair of electrons (the two dots) are drawn in between the two H symbols in the H 2 molecule. The molecule H 2 has ONE covalent bond. Each atom in the H 2 molecule has, by sharing, a single pair of electrons. Each H atom now has the electron configuration of a helium atom. It is said to be isoelec- tronic (having the same number of electrons) with a helium atom The helium atom electron configuration is very stable because it is a filled energy level. The red circles outline the structures isoelectronic to the helium atom. Lets form a covalent bond between two hydrogen atoms: Electronegativity There is a particularly simple and convenient way of showing the connections between covalently bound atoms. We do this by forming what are called Lewis diagrams. In Lewis diagrams the atoms are shown by writing the atomic symbol surrounded by one dot for each of the valence electrons. In a covalently bound molecule the dots are arranged in pairs, with the bound pairs placed between the atoms which they connect and the lone pairs at different sides of the atomic symbol.
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