1. Covalent Bonds
Atoms can form molecules by sharing electrons in the covalent bond. This is done only among non-metal atoms.

2. Molecules Some elements in nature are found in the form of molecules
Diatomic = 2 atoms
BrINClHOF
Compound composed
Of molecules is called a
Molecular compound

3. PROPERTIES Relatively low melting points and boiling points
Many are gases and liquids at room temperature
Composed of atoms of 2 or more nonmetals

4. Molecular Formulas
Show how many atoms of each element a molecule contains
Ex. H2O has 2 hydrogen atoms and 1 oxygen atom
Doesn’t show shape of molecule or which atoms are covalently bonded and how

5. Dot Structures-Octet Rule (All atoms want 8 electrons around them.)
Valence electrons are those in the outermost orbitals. They are the ones that can form bonds.
Electron sharing occurs in such a way so that atoms attain the electron configuration of the noble gases.

6. H H SINGLE COVALENT BONDS
Two atoms held together by sharing a pair of electrons. Can be shown by lewis dot or a dash
H H

7. UNSHARED PAIRS In F2 each flourine contributes one electron
The electrons that are not shared are called
Unshared pairs, lone pairs or nonbonding pairs

8. Draw Lewis structures
NH3
PCl3
Cl2
SBr2

9. DOUBLE AND TRIPLE COVALENT BONDS
Occurs when three pairs of electrons
Are shared
Occurs when two pairs of electrons are shared

10. NASL Method for Lewis Dot Structures
Helps to determine how to place electrons around an atom ( double/triple bonds + lone pairs)
Exceptions to octet = H = 2, Be = 4, B= 6
STEPS
Write a skeleton molecule with the lone atom in the middle (Hydrogen can never be in the middle)
Calculate (N) Needed which is the sum of electrons needed for all atoms to obey the octet rule.

11. NASL Method Show structure for CO2
O C O skeleton
2. Needed electrons
C = 1 x 8 = 8
O = 2 x 8 = 16
N = 24

12. NASL METHOD
Step 3; Calculate A (Available) = sum of all valence electrons. For anions and cations you need to subtract or add electrons here.
Step 4; Calculate S ( Shared) = Difference between N and A

13. CO2 Shared Needed – Available = 24-16= 8 1 x 4 = 4 for Carbon
2 x 6 = 12 for Oxygen
16 A (available)
Shared
Needed – Available = = 8

14. NASL Method
Divide S by 2 to obtain the number of bonds to be extended from the central atoms.
8 / 2 = O::C::O
Calculate L ( Lone-pair electrons ) the difference between A and S
16 – 8 =
O::C::O ●● ●●

15. Let's Try it! H O H S Water H2O N
2 x 2 = 4 for Hydrogen 1 x 8 = 8 for Oxygen 4+8=12 needed electrons
12 N -
8 H
2 x 1 = 2 for Hydrogen 1 x 6 = 6 for Oxygen You have 8 available electrons -
4 B
4 NB
12 – 8 = 4/2 = Bonding
H:O:H
8 – 4 = 4 non-bonding electrons ..
H:O:H ●● ..
H:O:H ●●

16. Let's Try it! H H N H S Ammonia NH3 N
3 x 2 = 6 for Hydrogen 1 x 8 = 8 for Nitrogen 6+8=14 needed electrons
14 N -
8 H
3 x 1 = 3 for Hydrogen 1 x 5 = 5 for Nitrogen You have 8 available electrons -
6 B
2 NB
14 – 8 = 6/2 = 3 bonding pairs H
.. H:N:H
8-6 = 2 lone electrons H H ..
H:N:H ●● ..
H:N:H ●●

17. REVIEW
Draw lewis dot structures for the following
PCL3
CH4

18. Review Quiz #2
Using NASL Show covalent bonding for the following compounds. Show all work for credit. ( 6 points )
SO2

19. Nomenclature Naming of Binary Molecular Compounds
Binary Compounds: Composed of two different elements that are nonmetals. Ex. CO and CO2 (not carbon Oxide) CO = Carbon monoxide = poisonous gas CO2 = carbon dioxide waste product of breathing Need to differentiate different types of compounds by using prefixes. Tells you how many of each element are present Mono = 1 Penta = 5 Di = 2 Hexa = 6 Tri = 3 Hepta = 7 Tetra = 4 Octa = 8

20. Naming Guidelines
1. make sure you have a binary molecular compound composed of two nonmetals
2. Name must identify the elements and how many are present
3. Name the elements in the order listed
4. Omit the prefix – mono when the first element only has one
Ex. SF6 is sulfur hexaflouride NOT monosulfur hexaflouride
5. The suffix for the second element is -ide

21. Writing Formulas
Use the prefixes in the name to determine the correct subscripts for the formula.
Ex. Silicon Carbide ( no prefixes so must contain one of each) SiC
Dinitrogen Tetroxide = N2O4

22. Let’s Practice! Phosphorus Pentachloride Iodine Heptaflouride
Chlorine triflouride
OF2
SO2
N2O4

23. Using a few sentences discuss what the cartoon might mean in terms of how Cl and H bond

24. POLARITY
Covalent bonds involve atoms sharing electrons (pulled in a tug of war)
When electrons are pulled equally = nonpolar Covalent bond
When electrons are pulled unequally = polar covalent bond

25. Electronegativity
The magnitude of attraction for electrons is called “Electronegativity”. The more electronegative an atom is, the more it wants the electrons.

26. The higher the electronegativity
Value the greater the ability to attract electrons

27. Bond types WATER IS A POLAR MOLECULE O = 3.5 ELECTRONEGATIVE
H = 2.1 ELECTRONEGATIVE
DIFFERENCE = 1.4 = POLAR COVALENT
OXYGEN PULLS HYDROGENS ELECTRONS CLOSER THAN HYDROGEN CAN PULL OXYGENS
ELECTRONS. OXYGEN GETS AN OVERALL PARTIAL NEGATIVE CHARGE AND HYDROGEN
GETS AN OVERALL PARTIAL POSTITIVE CHARGE DESIGNATED BY A GREEK DELTA SIGN

28. VSEPR Theory
Electron dot structures fail to reflect the 3-dimensional shape of molecules
Molecules in reality are 3 dimensional and can be explained by the VSEPR theory

29. VSEPR Theory Explains 3-D shape of molecules
Based on the theory that repulsion occurs between electron pairs and causes a variety of molecular shapes.
Electrons want to stay as far apart as possible
Can be determined by first looking at the lewis dot structure
Counting how many electron clouds (pairs) are radiating

30. LINEAR MOLECULES
The simplest structure has two groups around the central atom. Carbon monoxide, CO2, is an example of this kind of shape. The two groups of electrons in the two double bonds repel each other and assume a shape with an angle of 180 degrees.

31. MOLECULAR SHAPES

32. Review Pyramidal = 3 bonding pairs And a lone pair
Trigonal planar = 3 bonding
No lone pairs