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LEWIS DIAGRAMS

LEWIS DIAGRAMS. Ionic Compounds. Use arrows to represent the transfer of electrons. The final structure will contain ions. Octet-Rule Covalent Compounds. Simple covalent compounds such as CH 4 may be done by pairing electrons from different atoms. The pairing is shown with circles.

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LEWIS DIAGRAMS

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  1. LEWIS DIAGRAMS

  2. Ionic Compounds • Use arrows to represent the transfer of electrons. • The final structure will contain ions.

  3. Octet-Rule Covalent Compounds • Simple covalent compounds such as CH4 may be done by pairing electrons from different atoms. The pairing is shown with circles. • More complex covalent compounds and polyatomic ions should be drawn using the Need-Have Method.

  4. The Process For Drawing LD Diagrams • Determine the total number of valence electrons available. • Draw the diagram placing the central atom in the middle and the surrounding atoms around it. Put a pair of electrons between the atoms for the bonds then complete the octets for all external atoms. • If the central atom does not have a full octet, use electrons from the external atoms to create a multiple bond between the central atom and an exterior atom.

  5. Non-Octet Compounds • Some compounds will contain central atoms that do not follow the octet rule. • The four possibilities for non-octet compounds are: • Where more than 4 atoms are bonded to the central atom such as PCl5. • A noble gas is participating in bonding such as XeF4. • Where the central atom has less than 8 valence electrons such as BH3. • Where molecules contain an odd number of nonbonding electrons such as NO.

  6. Drawing Non-Octet Diagrams • To draw non-octet compounds count the electrons that you have available in the structure. • Draw the diagram placing the central atom in the middle and the surrounding atoms around it. • Make a single bond between the central atom and each surrounding atom. • Make sure that all surrounding atoms have a full valence shell. • Place any extra electrons on the central atom (Make sure you only use as many electrons as you have)

  7. Resonance Structures • For some molecules, there are multiple ways of placing the electrons between the atoms. • Structures that differ only in the arrangement of the electrons are called RESONANCE STRUCTURES. • Resonance structures are indicated using a double headed arrow.

  8. Coordinate Covalent Bonds • A coordinate covalent bond results when both electrons in the bond are donated from the same atom. • To determine if a bond is coordinate covalent, compare the number of non-bonding electrons around an atom to the number of valence electrons the atom has.

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