Lewis Dot Structures for Covalent Compounds - Part 1 CLEAR & SIMPLE

Introduction to Lewis Dot Structures

  • Teaching focus: Writing Lewis dot structures for covalent compounds.

  • Steps outlined for writing Lewis structures.

Steps to Write Lewis Structures

Step 1: Count Total Valence Electrons

  • Example: Water (H2O)

    • Hydrogen has 1 valence electron (2 Hydrogens contribute 2 electrons).

    • Oxygen has 6 valence electrons.

    • Total = 1 + 1 + 6 = 8 valence electrons.

Step 2: Write the Skeleton Structure

  • Place the atom that needs the most electrons in the center (Oxygen for H2O).

  • Hydrogen cannot be a central atom; it can only form a duet, not an octet.

  • H2O skeleton structure: H - O - H

Step 3: Form Bonds with Valence Electrons

  • Use 2 valence electrons to form each covalent bond in the skeleton structure.

    • H2O: Place 2 electrons to bond H and O, resulting in 2 covalent bonds.

    • After using 4 electrons for bonds, 4 electrons remain.

Step 4: Complete Octets

  • Distribute the remaining valence electrons to achieve octets.

    • Place remaining 4 electrons: 2 around O and 2 around each H, satisfying octets and duets.

    • Result: Oxygen has 8 electrons, each Hydrogen has 2 electrons.

  • Covalent bonds are counted twice in ownership of shared electrons.

Types of Bonds

  • Single bond: A pair of shared electrons.

  • Double bond: Two pairs of shared electrons.

  • Triple bond: Three pairs of shared electrons.

  • Representation: Dots (electrons) or dashes (bonds).

Examples of Lewis Structures

1. Nitrogen Tribromide (NBr3)

  • Count valence electrons:

    • Nitrogen: 5, Bromine: 7 (x3) = 21 → Total = 26 electrons.

  • Skeleton: N in middle, Br on sides.

  • Distribute electrons forming single covalent bonds:

    • 6 electrons used for 3 bonds, 20 remaining.

  • Distribute remaining electrons to achieve octets:

    • All atoms satisfied with octets.

2. O2 - Oxygen gas

  • Count electrons: Each oxygen = 6 (2 O's) = 12 electrons.

  • Skeleton: O - O.

  • Form a bond and recognize need for octets:

    • Initially does not satisfy octet on one oxygen, which requires a double bond.

3. Carbon Dioxide (CO2)

  • Count valence electrons:

    • Carbon: 4, Oxygen: 6 (x2) = 16 electrons.

  • Skeleton: C in center, O on sides.

  • Use bonds and distribute remaining:

    • Result: Each O has 8 electrons, C has 8 (double bonds with O).

4. Carbon Monoxide (CO)

  • Count valence electrons: Carbon = 4, Oxygen = 6 → Total = 10 electrons.

  • Form skeleton and bonds:

    • Adjust bonds to form triple bond with coordinate covalent bonding from O.

5. Ozone (O3)

  • Count electrons: 6 (x3) = 18 electrons.

  • Skeleton: O - O - O.

  • Form bonds and achieve octets:

    • Result: One double bond, one single bond between three oxygen atoms.

Conclusion

  • Review of steps to create Lewis structures for covalent compounds.

  • Importance of achieving octets and understanding bond types.