1. Chemical Formulas and Composition Stoichiometry
Chapter 2

2. Stoichiometry
Describes the ___________ relationships among elements in compounds (composition stoichiometry) and among substances as they undergo chemical changes (reaction stoichiometry).

3. Dalton’s Atomic Theory
An element is composed of extremely small, indivisible particles called _____.
All atoms of a given element have ______ properties that are ______.
Atoms cannot be _____, ______, or ______ into atoms of another element.
______ are formed when atoms of different elements combine with one another in small whole-number ratios.
The relative _____ and ____ of atoms are constant in a given compound.

4. Atoms and Molecules
We know what atoms are and the fundamental particles that compose them.
_______ is the smallest particle of an element or compound that can have a stable, ______ existence.
This means that if a molecule contains only one type of atom it is also an element.

5. Atoms and Molecules Monatomic – contains only ___ atom
Na and He For these elements, an atom and a molecule are the same.
Diatomic – molecules that contain only __ atoms
H2, O2, and all halogens
Polyatomic – molecules than contain ______ atoms
P4, S8, and C60
Allotropes – different _____ (geometry or number of atoms) of the same element

6. Compounds
Compounds are substances that contain two or more elements in fixed proportions
Compounds containing only covalent bonds
The atoms in a compound _________ electrons.
These compounds are also called molecules since they exist as individual particles.
Compounds containing ionic bonds
These compounds are held together by electrostatic interactions.
These are not molecules since they do not exist as individual particles.

7. Covalent Compounds
The chemical formula represents the ____ present and the ______ in which the atoms of the elements occur.
Table 2.2 Show a few models to illustrate that all atoms are held together by covalent bonds.
H2O and C4H10 (models)
Notice that the formula is not necessarily the simplest ratio
_________ compounds are largely composed of C-C,C-H, and C-O bonds.
Ethanol and benzene

8. Covalent Compounds
Inorganic compounds largely do not contain _____ and/or ____ bonds.
H2O and NH3
Law of Definite Proportions – different pure samples of a compound always contain the same elements in the same proportion by mass
_______ of atoms can also affect the properties of compounds even if they have the same chemical formula.
Demo: John Cullen’s demonstration

9. Compounds Containing Ionic Bonds
Held together by __________ between ions
They do not exist as individual units
Collection of a large number of ions
The formula represents the ______ of ions in the compound
Each positively-charged species is surrounded by negatively-charged species (and vice-versa)
DEMO: NaCl structure

10. Writing Formulas and Names for Ionic Compounds (Table 2-3)
Positive and negative ions will combine in such a way to make the ionic compound _____.
Binary Ionic Compounds
You already know how to write the formulas.
Write the formula for calcium bromide and lithium sulfide
Naming a binary compound from the formula
Cation – name of the metal
Anion – drop the last portion of the name and add ‘ide’
Name AlBr3 and BeI2

11. Common Ions

12. More Polyatomic Ions

13. Writing Formulas and Names for Ionic Compounds (Table 2-3)
Ionic compounds containing a cation that can have multiple charges
The charge on the cation has to be specified
What is the charge on FeCl3 and FeCl2?
In most cases, the charge can be determined by the negatively-charged ion
Write the names for these compounds?
Write the formulas for copper(II) sulfide and iron(III) oxide.

14. Writing Formulas and Names for Ionic Compounds (Table 2-3)
Ionic compounds containing polyatomic ions
The atoms in polyatomic ions are held together by _________.
Write the Lewis structure for SO32-
The polyatomic ions and the oppositely-charged ions are held together in the solid by _________

15. Writing Formulas and Names for Ionic Compounds (Table 2-3)
Write the names for (NH4)2S and K2(SO4).
Notice that the charges are fixed and given on Table 2-3 for the polyatomic ions.
Write the formulas for magnesium nitrate and lithium carbonate.
If more than one polyatomic ion is needed parentheses are placed around it

16. Atomic Weight The atomic weight is based on the atomic mass unit.
One amu is _____ the mass of a carbon-12 atom
The atomic weight, which is given on the periodic table, is a _______ of all the naturally occurring isotopes of that element

17. The Mole
A mole describes a ________ of objects, particles, or atoms. This is similar to other measurements that describe a particular quantity.
1 dozen = 12 items
Gross = 144 items
1 mole = _____________ (much larger)
Avogardo’s number

18. The Mole
A mole is the amount of substance that contains as many entities as there are atoms in 12.0 grams of carbon-12.
One mole of H2O would contain 6.02  1023 molecules of H2O.
The mass of one mole of atoms of an element is equal to its atomic weight (periodic table) in grams.
This is called the molar mass (units ________).

19. The Mole Iron (Fe) These conversion factors will be used extensively!!
Calculate the mass of a single Mg atom.
Calculate the number of atoms in 1.40  moles of Cu.
Calculate the number of moles in 85.3 grams of Al.

20. Molar Mass
The ________ of a substance is the sum of the atomic weights of all the atoms in the formula. Expressed in amu.
_________ can be used if the compound is composed of molecules.
Molar mass is _________ to the formula weight of a compound. Expressed in grams
Indicates how many grams in ______ of the compound

21. Molar Mass
This molar mass of a substance will contain 6.02  1023 formula units
What is the molar mass of Ca(NO3)2?
Calculate the number of C3H8 molecules in 75.4 grams of C3H8
Calculate the number of millimoles in g of oxalic acid (CHOO)2

22. More Problems
The chemical formula indicates the relative number of ______ and _____ in a compound.
Shown by the ________ C3H8
How many formula units in 2.5 moles of CaCl2? How many Ca2+ and Cl- ions in 2.5 moles of CaCl2?
Calculate the number of oxygen atoms in 54.2 grams of sucrose, C6H12O6.
Calculate the number of moles of hydrogen in 54.2 grams of sucrose.

23. Percent Composition
The mass percent of each element present in a compound is simply determined by dividing its mass by the molar mass of the compound multiplied by 100%.
Let’s do H2O. What is the percent composition of oxygen and hydrogen?
What is the percent composition of carbon and hydrogen in C3H8?

24. Percent Composition
The percentages must add up to _____. Any pure compound will contain the same percentages of each element (____ __ _____ ________).
One more – What is the percent composition of Fe in Fe2(SO4)3?

25. Determining Empirical Formulas from Percent Composition
Empirical formula (or simplest formula) is the __________ ratio of elements in a compound.
Molecular formula is the ________ of atoms present in a compound containing covalent bonds.
The empirical formula and molecular formula are not necessarily the same.
Benzene (show structure) Molecular vs. empirical
Hydrogen peroxide (show structure) Molecular vs. empirical
Sucrose

26. Determining Empirical Formulas from Percent Composition
A compound contains 24.74% K, 34.76% Mn, and 40.50% O. What is the empirical formula of this compound?
Step 1: Consider how many grams of each element would be present in grams.
Step 2: Convert to moles for each element.
Step 3: Obtain smallest whole-number ratio by dividing by the smallest mole number.
Step 4: If necessary, convert fraction to whole numbers by multiplying an integer.

27. Determining Empirical Formulas from Percent Composition
A compound contains 7.537% H, % N, and % Cl. What is the empirical formula?
A sample of a compound contains grams of Co and grams of O. Find the simplest formula.

28. Combustions Train – Analysis of Hydrocarbons
Combustion trains are used to perform quantitative carbon-hydrogen analysis.
A known mass is burned in a stream of oxygen.
Carbon is converted to CO2
Hydrogen is converted to H2
Weight increase in the absorber region is measured.

29. Combustions Train – Analysis of Hydrocarbons
Determine the mass of carbon in the compound
Use the conversion factor
Determine the mass of oxygen in the compound
Why do we use these conversion factors?
Which units will cancel?

30. Combustions Train – Analysis of Hydrocarbons
A gram sample of pure hydrocarbon was burned in a combustion train to produce grams of H2O and grams of CO2. Determine the masses of C and H in the sample and the percentages of these elements in this hydrocarbon.
I’ll give you one on your chapter problems.

31. Combustions Train – Analysis of Hydrocarbons
Compounds that contain C, H, and O.
A gram compound containing on C, H, and O was burned in a combustion train to produce grams of CO2 and grams of H2O. Determine the masses of C, H, and O in the sample and the percentages of these elements in this hydrocarbon.

32. Determining Molecular Formulas
Percent composition only yields empirical formulas.
Determine the empirical formulas for the last two problems.
In order to determine the molecular formula, both the _______ and the _________ must be known.

33. Determining Molecular Formulas
The molecular formula is an integer multiple of the simplest formula.
C6H6 and C6H12O6
Molecular formula = n  simplest formula
It follows that;
Molecular weight = n  simplest formula weight (rearrange to solve for n)
The molecular weight of the compound in the first problem was determined to be amu. What is the molecular formula?

34. Determining Molecular Formulas
The molecular weight of the compound in the second problem was determined to be amu. What is the molecular formula?
Have fun!!!

35. More Fun with Conversions
What mass of ammonium phosphate, (NH4)3PO4 would contain exactly grams of N?
What mass of sucrose, C6H12O6, would contain the same mass of oxygen as is contained in 25.1 grams of ammonium phosphate?

36. Solid Hydrates
Solid hydrates are crystalline solids that contain _______ which can be generally removed by heating.
DEMO: CuSO45H2O The water can be removed by heating.
Every mole of CuSO45H2O contains _____ of water.
An unidentified hydrate of magnesium sulfate is heated, MgSO4xH2O. The mass before heating was grams. The new mass after heating is grams. What is the formula of the hydrate?

37. Purity of Samples
Samples are never 100% pure. Percent purity is used to specify the purity of a particular sample.
In many cases, 100 grams of sample can be used for convenience.
A bottle of Na3PO4 is 98.3% pure. What are the masses of Na3PO4 and impurity in 251 grams of sample?
Calculate the number of moles of C2H4Cl2 in 58.2 g of 92.1% pure C2H4Cl2.

38. Solving Problems

39. Let’s Do Some More Problems