1. Chapter 8 Covalent Bonding 8.1 Molecular Compounds
8.2 The Nature of Covalent Bonding
8.3 Bonding Theories
8.4 Polar Bonds and Molecules
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2. Molecules and Molecular Compounds
In nature, only the noble gas elements exist as uncombined atoms.
They are monatomic; that is, they consist of single atoms.
Helium, which is less dense
than air, is often used to
inflate balloons.
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3. Molecules and Molecular Compounds
There are two ways elements can be like the nearest noble gas.
Transfer electrons to form an ionic compound.
Share electrons to form covalent compounds.
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4. Electronegativity – ability of an atom to attract electrons when it is in a compound.
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5. Molecules and Molecular Compounds
The electronegativity difference between two atoms tells you what kind of bond is likely to form.
>2.0 tends to form an ionic bond
<2 tends to form a covalent bond
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6. Molecules and Molecular Compounds
Covalent bond: a bond in which atoms are held together through the sharing of electrons
Electron sharing usually occurs so that atoms attain the electron configuration of noble gases
Molecule: a neutral group of atoms joined together by covalent bonds
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7. Molecules and Molecular Compounds
Work out how Flourine atoms would share electrons to form covalent bonds.
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8. Molecules and Molecular Compounds
Covalent bond: a bond in which atoms are held together through the sharing of electrons
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9. Molecules and Molecular Compounds
Molecule: a neutral group of atoms joined together by covalent bonds
Examples: F2
H2O
CH4
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10. Molecules and Molecular Compounds
Diatomic molecule—a molecule that contains two atoms.
Other elements found in nature in the form of diatomic molecules include hydrogen, nitrogen, oxygen, and the halogens.
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11. Molecules and Molecular Compounds
Draw the electron dot structures for the following molecules.
Chlorine
Bromine
Iodine
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12. Molecules and Molecular Compounds
Molecules can also be made of atoms of different elements.
- Examples: H2O (water), CO2 (carbon dioxide), and N2O (nitrous oxide)
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13. Molecules and Molecular Compounds
Molecular formula - chemical formula of a molecular compound.
shows how many atoms of each element a substance contains
H2O – 2 Hydrogen, 1 Oxygen
C4H10 – 4 Carbon, 10 Hydrogen
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14. Molecules and Molecular Compounds
Identify the number and kinds of atoms present in a molecule of each compound.
C6H8O6 – ascorbic acid (vitamin C)
C12H22O11 – sucrose (table sugar)
C7H5N3O6 – trinitrotoluene (TNT)
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15. Comparing Molecular and Ionic Compounds
Properties of Molecular Compounds
Lower melting and boiling points than ionic compounds
Gases or liquids at room temperature
Composed of atoms of two or more nonmetals
Do not conduct electricity
Usually do not dissolve in water as well as ionic compounds
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16. The Octet Rule in Covalent Bonding
Structural Formula: represents the covalent bonds as dashes and shows the arrangement of covalently bonded atoms.
H:H H-H
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17. The Octet Rule in Covalent Bonding
Single Covalent Bond: atoms held together by sharing one pair of electrons
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18. The Octet Rule in Covalent Bonding
Double Covalent Bond: a bond that involves two shared pairs of electrons
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19. The Octet Rule in Covalent Bonding
Triple Covalent Bond: a bond formed by sharing three pairs of electrons
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20. Bond Dissociation Energies
Bond Dissociation Energy: energy required to break the bond between two covalently bonded atoms.
Bond
Bond Dissociation Energy
(kJ/mol)
Bond Length
(pm)
C C
347
154
C = C
657
133
908
121
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21. The Octet Rule of Covalent Bonding
Draw Lewis Dot Structures for each molecular compound:
SiO2
HCl
H2O
HCN
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22. The Octet Rule of Covalent Bonding
Drawing Lewis Dot Structures:
Determine # of valence electrons.
Determine # of “octet” electrons.
*Note*– Hydrogen gets 2
# bonds = (# octet e- - # valence e- )
Arrange atoms with # bonds from step 3.
Hydrogen & halogens bond one time
Group 6A elements bond 2 times
Group 5A elements bond 3 times
Carbon always bonds 4 times
Add electron pairs until all atoms have the correct number of electrons around them
Recheck your answer.
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23. The Octet Rule of Covalent Bonding
Exceptions to the Octet Rule
Molecules whose total number of valence electrons is an odd number.
2. Boron wants 6 electrons for neutral molecules.
3. Phosphorus and sulfur expand the octet to 10 or 12 electrons.
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24. The Octet Rule of Covalent Bonding
Resonance structures: structures that occur when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion.
The ozone molecule has two possible electron dot structures.
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25. Comparing Molecular and Ionic Compounds
Water, which is a molecular compound, and sodium chloride, which is an ionic compound, are compared here.
Array of
sodium ions and
chloride ions
Collection of
water molecules
Formula unit of
sodium chloride
Molecule of
water
Chemical formula
H2O
NaCl
Chemical formula
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26. Molecules and Molecular Compounds
Classify compounds into groups according to their chemical bonding (ionic, covalent, or metallic).
High or low melting point? Conduct electricity?
Sodium chloride, NaCl
Ammonia, NH3
Methane, CH4
Magnesium Oxide, MgO
Aluminum, Al
Barium Iodide, BaI2
Magnesium, Mg
Cesium, Cs
Oxygen, O2
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27. END OF 8.1
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