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Covalent Bonding & Molecular Compounds. Depicting Molecular Compounds. Key Terms. A molecule is a neutral group of atoms that are held together by covalent bonds. A molecular compound is a chemical compound whose simplest units are molecules.

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covalent bonding molecular compounds

Covalent Bonding & Molecular Compounds

Depicting Molecular Compounds

key terms
Key Terms
  • A moleculeis a neutral group of atoms that are held together by covalent bonds.
  • A molecular compoundis a chemical compound whose simplest units are molecules.
  • A chemical formulaindicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscripts.
  • A molecular formulashows the types and numbers of atoms combined in a single molecule of a molecular compound.
  • A diatomic moleculeis a molecule containing only two atoms.
formation of a covalent bond
Formation of a Covalent Bond
  • Describe what happens to potential energy as a bond forms.
  • As a covalent bond forms, the attractive forces between the atoms overpower the repulsive forces between the atoms.
  • When the bond

has formed,

potential energy

is at a minimum.

characteristics of covalent bonds
Characteristics of Covalent Bonds
  • Bond lengthis the average distance between two bonded atoms.
  • By sharing electrons,

each H atom has

a full 1s orbital.

  • Bond energyis the energy required to break a chemical bond and form neutral, isolated atoms.
bond length vs bond energy
Bond Length vs. Bond Energy
  • As bond length decreases, bond energy increases.
  • As bond length increases, bond energy decreases.
  • Therefore, the relationship between bond length and bond energy is an inverse relationship.
the octet rule
The Octet Rule
  • Chemical compounds tend to form so that each atom has an octet of electrons in its highest occupied energy level.
    • Octet = 8 electrons.
    • An octet results

in fully filled

s + p orbitals.

exceptions to the octet rule
Exceptions to the Octet Rule
  • 1. Some elements are satisfied with fewer than 8 valence electrons:
    • Hydrogen only needs 2 valence electrons (1 bond).
    • Beryllium only needs 4 valence electrons (2 bonds).
    • Boron only needs 6 valence electrons (3 bonds).
  • 2. Some elements can be surrounded by more than eight electrons when they bind to highly electronegative atoms (F, O, Cl). Called an expanded octet.
lewis structures
Lewis Structures
  • Electron-dot notation used to represent molecules.
    • Dotsrepresent unshared electrons.

:

    • Dashesrepresent shared electron pairs.

-

      • A shared pair of dots (electrons) is replaced with a dash.
      • A single dash represents a single bond.
steps for drawing lewis structures
Steps for Drawing Lewis Structures
  • 1. Determine the type and number of atoms in the molecule.
    • For CH3I the atoms are:
      • 1 carbon, 3 hydrogen and 1 iodine.
    • Obtain the correct element cards from the bag.
steps for drawing lewis structures1
Steps for Drawing Lewis Structures
  • 2. Write the electron-dot notation for each type of atom and then determine the total number of valence electrons.
    • Use different colored beads to represent the valence electrons around each type of atom.
    • C = 1 atom x 4 valence electrons = 4 val e-
    • H = 3 atoms x 1 valence electron = 3 val e-
    • I = 1 atom x 7 valence electrons = 7 val e-
    • TOTAL = 14 valence electrons
steps for drawing lewis structures2
Steps for Drawing Lewis Structures
  • 3. Place atom with most open spaces (single electrons) in the middle.
    • Carbon will always be in the center if it is present.
    • Hydrogen and halogens will never be centrally located.
    • Arrange cards around the central atom.
steps for drawing lewis structures3
Steps for Drawing Lewis Structures
  • 4a. Make sure each element (except hydrogen) is surrounded by eight valence electrons.
    • If not all atoms are surrounded by 8 valence electrons, move electron pairs to form double or triple bonds.
      • Hydrogen and halogens will never form double or triple bonds.
steps for drawing lewis structures4
Steps for Drawing Lewis Structures
  • 4b. Replace bonding electron pairs with dashes.
    • Replace bonding electron pairs (beads) with straw sticks
  • 5. Check work by counting number of valence electrons.
    • Should have same number of electrons as in step 2.
double bond example
Double Bond Example

CH2O

  • Step 1:
    • 1carbon, 2 hydrogen, 1 oxygen
  • Step 2:
    • 12 total valence electrons.
  • Step 3:
double bond example1
Double Bond Example
  • Step 4a:
    • Carbon and oxygen are both one electron short. Move an electron pair between oxygen and carbon.
  • Step 4b:
  • Step 5:
    • Final structure has 12 valence electrons (same as in step 2).
triple bond example
Triple Bond Example

CO

  • Step 1:
    • 1carbon & 1 oxygen
  • Step 2:
    • 10 total valence electrons.
  • Step 3:
triple bond example1
Triple Bond Example
  • Step 4a:
    • Move two electron pairs between oxygen and carbon to satisfy octet rule for both.
  • Step 4b:
  • Step 5:
    • Final structure has 10 valence electrons (same as in step 2).
single vs multiple bonds
Single vs. Multiple Bonds
  • Single bondsconsist of one shared electron pair.
  • Multiple bondsconsist of two of more shared electron pairs.
    • Double bonds have two shared electron pairs.
      • Have shorter bond length than single bonds.
      • Have greater bond energy than single bonds.
    • Triple bonds have three shared electron pairs.
      • Have shorter bond length than double bonds.
      • Have greater bond energy than double bonds.
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