1. Chemistry 8.1
Covalent Bonds

2. Molecular Compounds
8.1
These toy models are made from circular pieces joined together in units by sticks. Atoms can also be arranged in different ways to make a variety of products.

3. Molecules and Molecular Compounds
8.1
Molecules and Molecular Compounds
Molecules and Molecular Compounds
In nature, matter takes many forms. The noble gases, including helium and neon, are monatomic. That means they exist as single atoms.
In Ch 7, you learned about ionic compounds that are composed of ions held together by the electrostatic attraction of opposite charges.
The noble gases, including helium and neon, are monatomic. That means they exist as single atoms. Helium, being less dense than air, is often used to inflate balloons. The colors produced in what we commonly call neon lights are a result of passing an electric current through one or more noble gases.

4. Molecules and Molecular Compounds
8.1
Molecules and Molecular Compounds
In some compounds the atoms are held together by sharing electrons
This is called a covalent bond.
A molecule is a neutral group of atoms joined together by covalent bonds.
A diatomic molecule is a molecule consisting of two atoms. An oxygen molecule is a diatomic molecule.

5. Molecules and Molecular Compounds
8.1
Molecules and Molecular Compounds
A compound joined by covalent bonds is called a molecular compound.
Water and carbon monoxide are molecular compounds.
Water is a molecular compound with molecules composed of two hydrogen atoms and one oxygen atom. Carbon monoxide is a molecular compound with molecules composed of one carbon atom and one oxygen atom.

7. Molecules and Molecular Compounds
8.1
Molecules and Molecular Compounds
Sodium chloride, which is an ionic compound, and water, which is a molecular compound, are compared here. Interpreting Diagrams How do molecular compounds differ from ionic compounds?

8. Molecules and Molecular Changes
8.1
Molecules and Molecular Changes
Ethane, a component of natural gas, is also a molecular compound.
Ethane is a component of natural gas. Inferring What information about the ethane molecule given by its molecular formula C2H6 is also given by the drawing shown here?

9. A molecular formula is the chemical formula of a molecular compound.
8.1
Molecular Formulas
A molecular formula is the chemical formula of a molecular compound.
A molecular formula shows how many atoms of each element a molecule contains.
C6H12O6
6 carbon atoms + 12 hydrogen atoms + 6 oxygen atoms

10. 8.1 Formulas of Some Molecular Compounds Molecular Formulas
The formula of a molecular compound indicates the numbers and kinds of atoms. The arrangement of the atoms within a molecule is called its molecular structure. Using Models Which of these molecules has the greatest number of oxygen atoms?

11. Representing Molecules
8.1
Representing Molecules
Ammonia (NH3) is used in solution as a cleaning agent. You can represent the ammonia molecule by its molecular formula, its structural formula, a space-filling molecular model, a perspective drawing, or by a ball-and stick molecular model.

12. Representing Molecules
8.2
Representing Molecules
An electron dot structure such as H:H represents the shared pair of electrons of the covalent bond by two dots.
A structural formula represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms.

13. The Octet Rule in Covalent Bonding
8.2
The Octet Rule in Covalent Bonding
Why do atoms share electrons?
To attain the electron configurations of noble gases.
Which is an octet of valence electrons.
(Does this make them a noble gas??? NO! )

14. The Octet Rule in Covalent Bonding
Molecular compounds can share one, ** two, ** ** or three ** ** ** pairs of electrons in order to achieve an octet of 8 electrons in their valence shell.

15. 8.2
Single Covalent Bonds
Single Covalent Bonds
Two atoms held together by sharing a pair of electrons are joined by a single covalent bond.

16. 8.2
Single Covalent Bonds
The halogens form single covalent bonds in their diatomic molecules. Fluorine is one example.

17. 8.2
Single Covalent Bonds
The hydrogen and oxygen atoms attain noble-gas configurations by sharing electrons.

18. 8.2
Single Covalent Bonds
A pair of valence electrons that is not shared between atoms is called an unshared pair, also known as a lone pair or a nonbonding pair.
The ammonia molecule has one unshared pair of electrons.

19. 8.2
Single Covalent Bonds
Methane has no unshared pairs of electrons.

20. Double and Triple Covalent Bonds
8.2
Double and Triple Covalent Bonds
Double and Triple Covalent Bonds
How do atoms form double or triple covalent bonds?
Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.
2 shared pairs = double covalent bond.
3 shared pairs = triple covalent bond.

21. Double and Triple Covalent Bonds
8.2
Double and Triple Covalent Bonds
These oxygen atoms share 2 pairs of electrons:
Oxygen and nitrogen are the main components of Earth’s atmosphere. The oxygen molecule is an exception to the octet rule. It has two unpaired electrons. Three pairs of electrons are shared in a nitrogen molecule.

22. Double and Triple Covalent Bonds
8.2
Double and Triple Covalent Bonds
These nitrogen atoms share 3 pairs of electrons:
Oxygen and nitrogen are the main components of Earth’s atmosphere. The oxygen molecule is an exception to the octet rule. It has two unpaired electrons. Three pairs of electrons are shared in a nitrogen molecule.

23. Bond Dissociation Energies
8.2
Bond Dissociation Energies
Bond Dissociation Energy: The energy required to break the bond between two covalently bonded atoms.
A large bond dissociation energy corresponds to a strong covalent bond.
A carbon–carbon single bond: kJ/mol.
Carbon–carbon double bonds: kJ/mol.
Carbon- carbon triple bonds: kJ/mol.
Strong carbon–carbon bonds help explain the stability of carbon compounds.

24. Covalent bonds in polyatomic ions
8.2
Covalent bonds in polyatomic ions
A polyatomic ion, such as NH4+, is a tightly bound group of atoms that has a positive or negative charge and behaves as a unit. It is held together by covalent bonds.
The polyatomic ammonium ion (NH4), present in ammonium sulfate, is an important component of fertilizer for field crops, home gardens, and potted plants.
The polyatomic ammonium ion (NH4+), present in ammonium sulfate, is an important component of fertilizer for field crops, home gardens, and potted plants.

25. 8.2
Resonance
Ozone, O3, in the upper atmosphere blocks harmful ultraviolet radiation from the sun.
At lower elevations, it contributes to smog.
Although ozone high above the ground forms a protective layer that absorbs ultraviolet radiation from the sun, at lower elevations ozone is a pollutant that contributes to smog.

26. 8.2
Resonance
Notice that it is possible to draw two valid electron dot structures for ozone:
A resonance structure is a structure that occurs when there are two or more valid electron dot structures for a molecule.
The actual bonding of oxygen atoms in ozone is a hybrid, or mixture, of the extremes represented by the resonance forms.

27. Exceptions to the Octet Rule
8.2
Exceptions to the Octet Rule
Exceptions to the Octet Rule
(Oh, nooo!!!!!)
Sometimes there will exist molecules with atoms that have fewer or more than an octet of valence electrons.

28. Exceptions to the Octet Rule
8.2
Exceptions to the Octet Rule
NO2 is produced naturally by lightning strikes.
Lightning is one means by which nitrogen and oxygen in the atmosphere produce nitrogen dioxide.

29. Exceptions to the Octet Rule
8.2
Exceptions to the Octet Rule
In PCl5, phosphorus has ten valence electrons.
In SF6, sulfur has twelve valence electrons!!
Phosphorus pentachloride, used as a chlorinating and dehydrating agent, and sulfur hexafluoride, used as an insulator for electrical equipment, are exceptions to the octet rule. Interpreting Diagrams How many valence electrons does the sulfur in sulfur hexafluoride (SF6 ) have for the structure shown in the figure?

30. How to Draw Lewis Dot Structures
1. Sum the valence electrons from all atoms.
If the molecule is a polyatomic anion, add 1 e- for each (-) charge.
If the molecule is a polyatomic cation, subtract 1 e- for each (+) charge.
2. Identify the central and terminal atoms and write the skeleton structure.
The central atom is usually the one with the lowest electronegativity (except H)
Tips: (H is always terminal) (C is always a central atom, it always has 4 bonds)
3. Draw a bond between each pair of atoms. (each uses 2 electrons)
4. Place remaining e- pairs around terminal elements until octet rule has been met (duet rule for H), or until you run out of electrons.
5. If there are leftover e-, place them on the central atoms to complete octets.
6. If all e- are used up and the central atoms do not have octets, move one or more lone pairs to form a double or triple bond.