1. Molecule Shape

2. VSEPR Model (Valence Shell Electron Pair Repulsion)
The structure around a given atom is determined principally by minimizing electron pair repulsions.

3. Predicting a VSEPR Structure
Draw Lewis structure.
Count the number of bonds. (count double and triple bonds as 1 bond)
Count the number of lone pair of electrons on the central atom
Determine the name of molecular structure from positions of the atoms from the chart.
9/16/2018

4. # of e- pairs 1 1 1 atom bonded to another atom # of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs
4 lone pairs 1
linear

5. # of e- pairs 2
2 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 2
linear

6. # of e- pairs 3
3 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 3
trigonal planar
bent / angular
linear

7. # of e- pairs 4
4 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 4
tetrahedral
trigonal pyramid
bent / angular
linear

8. # of Bonds 5
5 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 5
trigonal bipyramid
sawhorse / seesaw
t-shape
linear

9. # of e- pairs 6
6 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 6
Octahedral
square pyramid
square planar

10. pentagonal bipyramidal
# of e- pairs 7
7 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
# of e-pairs
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 7
pentagonal bipyramidal
pentagonal pyramidal

11. Determine the Molecular Shape of SCl2
3 . Count the number of lone pairs on central atom
1. Draw the Lewis structure Cl S Cl
20 e- total Cl S Cl
4 electron pairs (bonds and lone pairs)
2 lone pairs of electrons
2 . Count the number of bonds
4. Look at the chart and determine the shape! Cl S Cl
Bent

12. Determine the shape of these molecular compounds
1. PF3
2. CO2
26 e- total
16 e- total
3. NH4+
8e- total H + F P F O C O F N H H
Count the double bonds as “one” electron pair
4 electron pairs
(bonds and lone pairs)
1 lone pairs of electrons H
2 “electron pairs”
4 electron pairs
Linear
Trigonal pyramidal
Tetrahedral
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13. Click Below for the Video Lectures
Lewis Diagram and VSEPR

14. Molecular Polarity

15. Polarity The polarity can tell you many things:
How high or low the melting and boiling point of the substance is
How easily the liquid form of the substance evaporates
Whether the substance will dissolve in water, or in some other solvent

16. Polar Molecules
If the molecule does not have a symmetrical shape (asymmetrical), then there is a greater concentration of electrons on one side of the molecule compared to the other side.
This makes one side charged partially negative and the other side partially positive.
The oppositely charged ends of these molecules are “poles”, making the molecule polar.
Polar molecules can attract each other, δ+ end of one molecule attracting to the δ- end of the other molecule.

17. How to determine polarity
Draw structural formula
Check for line of symmetry – mirror image
Look up ENs of the atoms on the ends of symmetry
Draw an arrowhead on the side with the higher EN
The side with higher EN has greater pull of the e-s, so it is charged δ -. The other side is charged δ +.
3.2
2.1
H - Cl
δ +
δ -

18. How to determine polarityCl H
δ -
Draw structural formula
Check for line of symmetry – mirror image
Look up ENs of the atoms on the ends of symmetry
Draw an arrowhead on the side with the higher EN
The side with higher EN has greater pull of the e-s, so it is charged δ -. The other side is charged δ +.
3.2
Cl – C- Cl
δ +
2.1

19. Nonpolar Molecules
If the molecule has a symmetrical shape, then the electrons are distributed evenly through the molecule, and the whole molecule is nonpolar (even if it contains polar bonds).
Nonpolar molecules have equal pull of electrons on all sides of the molecule, so no side develops a pole.
Since the molecule lacks oppositely charged ends, any attractive forces will be extremely weak.

20. Nonpolar Molecules H
H – C- H
H– C - H
O = O

21. Molecular Force

22. Nonpolar molecules
form LONDON DISPERSION FORCE attractions. Since there are no permanent positive or negative ends, these attractions are extremely weak.
The attractions are a combination of temporary poles due to electron movement around the molecule or, in the case of huge molecules, they actually get tangled up with each other like sticky strands of spaghetti or yarn.
London dispersion forces generally get stronger as the size of the molecule increases.

24. London dispersion force

25. Polar molecules
form DIPOLE attraction: the simple attraction of the oppositely charged ends of two molecules.
The partially positive end of one molecule attracts to the partially negative end of a different molecule.
This attraction allows these substances to exist as solids and liquids at higher temperatures than are possible for nonpolar molecules of equivalent size.

27. H - Cl H - Cl H - Cl H - Cl δ - δ + δ + δ - δ + δ - 3.2 2.1 3.2 2.1

28. Hydrogen Bond Some polar molecules form HYDROGEN BONDS between them.
Bonding between hydrogen and more electronegative neighboring atoms; Nitrogen, Oxygen and Flourine (F,O,N)
An extremely high melting point, boiling point, heat of fusion and heat of vaporization for a molecule its size

29. Hydrogen Bonding in Water
The attraction between the two molecule is nearly that of ionic attraction.
Not only that but the H end of one molecule actually forms temperary covalent bonds with the N,O or F that makes up the end of the other molecule.
This gives extra strength that allows water to be liquid at room teperature despite its small size.

30. Nonpolar molecules
Polar molecules
London dispersion forces
Dipole – dipole
Hydrogen bond (F,O,N)

31. So, what should you be able to do now?
1) Identify whether a compound is molecular, ionic, metallic or network based on its properties 2) Draw dot diagrams of simple molecules 3) Draw structural formulas of simple molecules 4) Determine the shape of simple molecules 5) Determine if simple molecules are polar or nonpolar 6) If polar, draw the dipole moment and identify the partially charged ends 7) Determine the attractive force type that attracts specific simple molecules to each other.

32. Checking for understanding
Explain the difference between polar and nonpolar molecules
Explain London dispersion force
Explain dipole attraction forces including hydrogen bond

33. Click Below for the Video Lectures
Intermolecular forces Dipole Forces London Disperson forces

34. Chemical Formula

35. Click Below for the Video Lectures
Molecule and Elements

36. Molecular Formula
Molecular Formula - indicates the total number of atoms of each element needed to form the molecule.
MOLECULES ARE PARTICLES FORMED BY THE COVALENT BONDING OF NONMETAL ATOMS.
A molecule of methane contains one atom of carbon and four atoms of hydrogen, so the molecular formula is CH4.

37. Empirical Formula
Empirical Formulas represents the simplest ratio in which the atoms combine to form a compound.
Empirical formulas are used to represent ionic compounds which form crystals of alternating + and – charge instead of separate molecules.
CaCl2 is ionic, and the formula represents a ratio of 1 ion of Ca+2 to every 2 ions of Cl –
Empirical formulas of covalent compound show the smallest ratio of atoms possible
formula C3H8 may represent molecular formula
C3H8 or C6H16

38. Interpreting chemical formula
The subscript tells you how many moles of that particular ion you have in one mole of the compound.
A Mole is to chemistry what a “dozen” is to donuts or eggs. Chemical formulas and reactions are written by the mole. 1 mole = 6.02 X 1023 of anything.
The mole is a unit of measurement for amount of a substance 1 mole = 6.02 X of anything
If there is no subscript, then the number of moles of that ion is 1.
When Interpreting Formulas, if there are (parentheses) around the element, any subscript outside the parentheses multiplies all of the elements inside the parentheses by that amount.

40. Ca(NO3)2 Ca(NO3)2 1 mol Ca , 2 mol N, 6 mol O 6.02x1023 atoms of Ca
2 outside the parentheses, so double the number of atoms inside to get the total number of atoms of that element (2 N’s and 6 O’s).
Since Ca is not inside the parentheses, it is not doubled. There is only 1 Ca in the formula.
1 mol Ca , 2 mol N, 6 mol O
6.02x1023 atoms of Ca
2 x (6.02x1023 ) atoms of N
6 x (6.02x1023 ) atoms of O

41. Checking for understanding
Complete the chart bellow, an example was done for you
BaCO3
1mol Ba
1mol C
3mol O
Na3PO4
Al2(SO4)3

42. Molar Mass

43. Molar Mass of an Element
Here are the elements that are in the compounds in the examples of how to determine the gram formula mass.
Molar Mass of CO2
= 1 x g/mol
44.01 g/mol
+ 2 x g/mol =

44. Mole Conversion

45. Mole Map moles grams atoms Circle the numbers
Molar
Mass
atoms
6.02x1023
Circle the numbers
Underline what you are looking for
Start with what you circled
Check your answer with number of sig figs.

46. Mass to Mole Conversion
How many moles of carbon is
26 g of carbon?
26 g C
1 mol C
12.01 g C
= 2.2 mol C
Molar
Mass
moles
grams

47. How many moles is 5.69 g of Na? 5.69 g Na 1 mol Na 22.99 g Na moles
Molar
Mass
moles
grams 47

48. How many grams are in 9.45 mol of nitrogen atoms?
9.45 mol N
14.01 g N
1 mol N =
=132 g N
Molar
Mass
moles
grams 48 48

49. Remember… 1 Mole = 6.02 x 1023 atoms or molecules

50. Molar Conversion Examples
How many atoms are in 2.50 moles of C?
6.02  1023 atoms
1 mol
2.50 mol
1.51  1024
=atoms C
6.02x1023
atoms
moles

51. Calculate the number of atoms in 0.500 mol of Al.
3.01  1023
=atoms Al
6.02x1023
atoms
moles

52. Calculate the number of moles of 1.80 x 1024 Na atoms.
1.80 x 1024 atoms
= 2.99 moles
6.02x1023
atoms
moles

53. dinitrogen trioxide, N2O3 ?
How many grams are in
1.20 x1024 molecules of
dinitrogen trioxide, N2O3 ?
1.20  1024
molecules
1 mol
6.02  1023
molecules
76.02 g
1 mol
= g
=152 g N2O3
Molar
Mass
6.02x1023
atoms
moles
grams 53 53 53 53

54. Find the mass of 2.1  1024 molecules of NaHCO3. 2.1  1024 molecules
6.02  1023
molecules
84.01 g
1 mol
= 290 g NaHCO3
Molar
Mass
6.02x1023
atoms
moles
grams 54 54 54 54 54

55. Checking for understanding
1. How many atoms are in 5g of Ca?
2. How many atoms are in 1.2 mol K?
3. Calculate the mass of 1.4x molecules
of CaCO3

56. Click Below for the Video Lectures
The Mole

57. Percent Composition

58. Percent Composition by Mass
Part
X 100 %
Whole
The proportion by mass of the elements in a compound
Experimental Percent Composition
given mass of element in sample
X 100 %
given mass of total sample

59. Total = 80.0 g O = 56.0 g N = 24.0 g % O = (56.0g/80.0g) X 100 = 70.0%
A compound containing nitrogen and oxygen has a mass of 80.0 grams. Experiments show that the 80.0 grams is made up of 56.0 grams of oxygen and 24.0 grams of nitrogen. What is the % composition, by mass, of each element in the compound?
Total = 80.0 g
O = 56.0 g
N = 24.0 g
% O = (56.0g/80.0g) X 100 = 70.0%
%N = (24.0g/80.0g) X 100 = 30.0%

60. X 100 % Percent Composition
2) Determination by formula: You need the periodic table to do this.
mass of element in compound
X 100 %
mass of compound

61. What is the % composition, by mass, of each element in SiO2?
Molar mass of SiO2
= g + (2 x 16.00g ) = 60.1 g
%Si = (28.1g/60.1g) X 100 = 46.8%
%O = ( 32 g / 60.1 g) X 100 = 53.2%

62. Checking for understanding
Calculate the % composition, by mass, of each element in Al(OH)3