1. Compounds & Molecules NaCl, salt Ethanol, C2H6O Buckyball, C60
To play the movies and simulations included, view the presentation in Slide Show Mode.
Buckyball, C60

2. Compounds & Molecules
COMPOUNDS are a combination of 2 or more elements in definite ratios by mass.
The character of each element is lost when forming a compound.
MOLECULES are the smallest unit of a compound that retains the characteristics of the compound.

3. MOLECULAR FORMULAS Formula for glycine is C2H5NO2
In one molecule there are
2 C atoms
5 H atoms
1 N atom
2 O atoms

4. WRITING FORMULAS H2NCH2COOH to show atom ordering
Can also write glycine formula as
H2NCH2COOH to show atom ordering
or in the form of a structural formula

5. MOLECULAR MODELING
Drawing of glycine
Ball & stick
Space-filling

6. Resources for Molecular Modeling
Modeling software on the General Chemistry Interactive CD-ROM
CAChe — see the folder labeled CAChe on the CD-ROM
Rasmol

7. MOLECULAR WEIGHT AND MOLAR MASS
Molecular weight = sum of the atomic weights of all atoms in the molecule.
Molar mass = molecular weight in grams

8. What is the molar mass of ethanol, C2H6O?
1 mol contains
2 mol C (12.01 g C/1 mol) = g C
6 mol H (1.01 g H/1 mol) = g H
1 mol O (16.00 g O/1 mol) = g O
TOTAL = molar mass = g/mol

9. Tylenol
Formula =
Molar mass =
C8H9NO2
151.2 g/mol

10. Molar Mass

11. How many moles of alcohol are there in a “standard” can of beer if there are 21.3 g of C2H6O?
(a) Molar mass of C2H6O = g/mol
(b) Calc. moles of alcohol

12. How many molecules of alcohol are there in a “standard” can of beer if there are 21.3 g of C2H6O?
We know there are mol of C2H6O.
= x 1023 molecules

13. How many atoms of C are there in a “standard” can of beer if there are 21.3 g of C2H6O?
There are 2.78 x 1023 molecules.
Each molecule contains 2 C atoms.
Therefore, the number of C atoms is
= x 1023 C atoms

14. Molecular & Ionic Compounds
Heme
NaCl

15. ELEMENTS THAT EXIST AS MOLECULES
Allotropes of C
See SCREEN 3.2 on the CD-ROM

16. Screen 3.2

17. ELEMENTS THAT EXIST AS DIATOMIC MOLECULES

18. ELEMENTS THAT EXIST AS POLYATOMIC MOLECULES
S8 sulfur molecules
White P4 and polymeric red phosphorus

19. IONS AND IONIC COMPOUNDS see Screen 3.5
IONS are atoms or groups of atoms with a positive or negative charge.
Taking away an electron from an atom gives a CATION with a positive charge
Adding an electron to an atom gives an ANION with a negative charge.

20. Forming Cations & Anions
A CATION forms when an atom loses one or more electrons.
An ANION forms when an atom gains one or more electrons
F + e- --> F-
Mg --> Mg e-

22. PREDICTING ION CHARGES
See CD-ROM Screen 3.5 and book Figure 3.7
In general
metals (Mg) lose electrons ---> cations
nonmetals (F) gain electrons ---> anions

23. Charges on Common Ions -4 -3 -2 -1 +1 +2 +3
By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.

24. Predicting Charges on Monatomic Ions

25. METALS M ---> n e- + Mn+ where n = periodic group Na+ sodium ion
Mg2+ magnesium ion
Al3+ aluminum ion
Transition metals --> M2+ or M are common
Fe2+ iron(II) ion
Fe3+ iron(III) ion

26. NONMETALS C4-,carbide N3-, nitride O2-, oxide F-, fluoride
NONMETAL + n e > Xn- where n = 8 - Group no.
Group 7A
Group 6A
Group 4A
Group 5A
C4-,carbide
N3-, nitride
O2-, oxide
F-, fluoride
S2-, sulfide
Cl-, chloride
Br-, bromide
I-, iodide

27. Ion Formation
Reaction of aluminum and bromine

28. POLYATOMIC IONS CD Screen 3.6
Groups of atoms with a charge.
MEMORIZE the names and formulas in Table 3.1, page 89.

30. Polyatomic Ions
NO3-
nitrate ion
HNO3
nitric acid

31. Polyatomic Ions NH4+ ammonium ion
One of the few common polyatomic cations

32. Polyatomic Ions CO32- carbonate ion HCO3- bicarbonate ion
hydrogen carbonate

33. Polyatomic Ions
PO43-
phosphate ion
CH3CO2-
acetate ion

34. Polyatomic Ions
SO42-
sulfate ion
SO32-
sulfite ion

35. Polyatomic Ions
NO3-
nitrate ion
NO2-
nitrite ion

36. COMPOUNDS FORMED FROM IONS
CATION +
ANION --->
COMPOUND
Na+ + Cl- --> NaCl
A neutral compd.
requires
equal number of +
and - charges.

37. IONIC COMPOUNDS
NH4+
Cl-
ammonium chloride, NH4Cl

38. Some Ionic Compounds Ca2+ + 2 F- ---> CaF2 Mg2+ + NO3- ---->
magnesium nitrate
Fe PO >
Fe3(PO4)2
iron(II) phosphate
(See CD, Screen 3.11 for naming practice)
calcium fluoride

39. Properties of Ionic Compounds Forming NaCl from Na and Cl2
A metal atom can transfer an electron to a nonmetal.
The resulting cation and anion are attracted to each other by electrostatic forces.

40. Electrostatic Forces
The oppositely charged ions in ionic compounds are attracted to one another by ELECTROSTATIC FORCES.
These forces are governed by COULOMB’S LAW.

41. Electrostatic Forces COULOMB’S LAW
As ion charge increases, the attractive force _______________.
As the distance between ions increases, the attractive force ________________.
This idea is important and will come up many times in future discussions!

42. Importance of Coulomb’s Law
NaCl, Na+ and Cl-,
m.p. 804 oC
MgO, Mg2+ and O2-
m.p oC

43. Molecular Compounds Compounds without Ions
CO2 Carbon dioxide
CH4 methane
BCl3 boron trichloride

44. Naming Molecular Compounds
All are formed from two or more nonmetals.
CO2 Carbon dioxide
Ionic compounds generally involve a metal and nonmetal
(NaCl)
BCl3 boron trichloride
CH4 methane

45. Empirical & Molecular Formulas
A pure compound always consists of the same elements combined in the same proportions by weight.
Therefore, we can express molecular composition as PERCENT BY WEIGHT
Ethanol, C2H6O
52.13% C
13.15% H
34.72% O

46. Percent Composition
Consider some of the family of nitrogen-oxygen compounds:
NO2, nitrogen dioxide and closely related, NO, nitrogen monoxide (or nitric oxide)
Chemistry of NO, nitrogen monoxide
Structure of NO2

47. Percent Composition Consider NO2, Molar mass = ?
What is the weight percent of N and of O?
What are the weight percentages of N and O in NO?

48. How to Determine a Formula?
Mass spectrometer

49. Mass Spectrum of Ethanol
(from the NIST site)
CH2O+ 31
CH3CH2O+ 45
CH3CH2OH+ 46

50. Determining Formulas
In chemical analysis we determine the % by weight of each element in a given amount of pure compound and derive the EMPIRICAL or SIMPLEST formula.
PROBLEM: A compound of B and H is 81.10% B. What is its empirical formula?

51. A compound of B and H is 81.10% B. What is its empirical formula?
Because it contains only B and H, it must contain 18.90% H.
In g of the compound there are g of B and g of H.
Calculate the number of moles of each constitutent.

52. A compound of B and H is 81.10% B. What is its empirical formula?
Calculate the number of moles of each element in g of sample.

53. A compound of B and H is 81.10% B. What is its empirical formula?
Now, recognize that atoms combine in the ratio of small whole numbers.
1 atom B + 3 atoms H --> 1 molecule BH3 or
1 mol B atoms + 3 mol H atoms ---> mol BH3 molecules
Find the ratio of moles of elements in the compound.

54. A compound of B and H is 81.10% B. What is its empirical formula?
Take the ratio of moles of B and H. Always
divide by the smaller number.
But we need a whole number ratio.
2.5 mol H/1.0 mol B = 5 mol H to 2 mol B
EMPIRICAL FORMULA = B2H5

55. A compound of B and H is 81. 10% B. Its empirical formula is B2H5
A compound of B and H is 81.10% B. Its empirical formula is B2H5. What is its molecular formula?
Is the molecular formula B2H5, B4H10, B6H15, B8H20, etc.?
B2H6 is one example of this class of compounds.
B2H6

56. A compound of B and H is 81. 10% B. Its empirical formula is B2H5
A compound of B and H is 81.10% B. Its empirical formula is B2H5. What is its molecular formula?
We need to do an EXPERIMENT to find the MOLAR MASS.
Here experiment gives 53.3 g/mol
Compare with the mass of B2H5
= g/unit
Find the ratio of these masses.
Molecular formula = B4H10

57. Determine the formula of a compound of Sn and I using the following data.
Reaction of Sn and I2 is done using excess Sn.
Mass of Sn in the beginning = g
Mass of iodine (I2) used = g
Mass of Sn remaining = g
See p. 104

58. Tin and Iodine Compound
Find the mass of Sn that combined with g I2.
Mass of Sn initially = g
Mass of Sn recovered = g
Mass of Sn used = g
Find moles of Sn used:

59. Tin and Iodine Compound
Now find the number of moles of I2 that combined with 3.83 x 10-3 mol Sn. Mass of I2 used was g.
How many mol of iodine atoms?
= x 10-2 mol I atoms

60. Tin and Iodine Compound
Now find the ratio of number of moles of moles of I and Sn that combined.
Empirical formula is SnI4