Valence Electrons and Lewis Dot

Valence electrons

• Located in the outermost electron shell

  • least tightly held by the atom

• Participate in bonds and electrons

  • reactivity

  • electronegativity

  • # bond formation

• Group number determines the number of valence electrons

  • Na is in group 1, which has one valence electron

    • electron configuration: 1s2 2s2 2p6 3s1

  • Chlorine is in group 7, which has 7 valence electrons

    • 1s2 2s2 2p6 3s2 3p5

• Octet: full eight electrons

  • noble gases except He

Lewis Dot

• Lewis Theory

  • atoms will form bonds with their valence electrons to fill their outer orbitals to mimic the electron configuration of the noble gases (octet rule)

• Procedure for drawing Lewis Structures

  • Step 1: count the number of valence electrons

  • Step 2: find the # electrons needed to fulfill octet rule

  • Step 3: Determine the # bonds in the molecule

    • (Step 2-Step 1)/2

  • Step 4: Choose a Central Atom

    • Often the least electronegative

      • Electronegativity DECREASES moving DOWN a group and INCREASES moving from LEFT to RIGHT across a period

      • Hydrogen and halogen atoms tend to appear on the outside of the molecules

  • Step 5: Draw a skeletal structure

    • Connect the atoms to the central atoms with a straight line representing a bond between the two atoms

    • Central atoms must have 4 atoms around it

  • Step 6: Place electrons around outside atoms

    • Complete the octets around each of the outer atoms

  • Step 7: Complete the octet for the central atom with the remaining electrons

  • Leftover bonds should be created as double bonds with lone pairs