1. Atoms, Molecules, and Ions
Chapter 2

2. 2.6 Molecules, Compounds, and Formulas
A molecule is the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of the substance.

3. Molecules, Compounds, and Formulas
How do molecules differ from their composite elements?
molecular formula
gives composition (ex. Ethanol C2H6O)
condensed formula
elements are written as groups (CH3CH2OH)
structural formula
shows how elements are attached

4. Molecular Models
ball and stick model
space filling model

5. 2.7 Ionic Compounds: Formulas, Names, and Properties
ionic compounds consist of charged atoms, or ions
cations and anions
metals generally lose electrons
nonmetals generally gain electrons

6. Ions monatomic – How can you determine charge?
Group A elements have predictable patterns of behavior, but Group B elements do not!
polyatomic ions
see chart p 69 in book – MEMORIZE!!

7. Ionic Formulas and Names
cation is written first followed by the anion; use parentheses if more than one polyatomic ion is present
name of the metal plus the word “cation”
Ba+2 is barium cation
if metal can form more than one ion, then use Roman numerals to indicate the charge
Hg+ is mercury (I)

8. Ionic Formulas and Names
the ending on an anion is changed to –ide
F- is fluoride (halide ions)
polyatomic ions keep their ending
SO4-2 is sulfate (oxoanions)
prefixes tell how much oxygen is present
Chlorine oxoanions are good examples!

9. Properties of Ionic Compounds
electrostatic forces hold ions together
force of attraction or repulsion between ions is Coulomb’s law
The force between two charged particles is proportional to the magnitude of the charges (attraction between ions increases as ion charge increases)
The force is inversely proportional to the square of the distance (attraction decreases as distance between the ions increases).

10. Properties of Ionic Compounds
ionic compounds are three dimensional arrays of atoms called a crystal lattice
high melting points due to the great attraction between ions

11. 2.8 Molecular Compounds: Formulas, Names, and Properties
can be gases, liquids, or solids
The first nonmetal is named, the second is named with an –ide ending.
HCl hydrogen chloride
The number of atoms of a given type is indicated by using a prefix.
N2O dinitrogen monoxide
Some have common names
CH4 methane, NH3 ammonia

12. 2.9 Atoms, Molecules, and the Mole
The mole is the chemical unit measuring amount of substance.
1 mole = x 1023 particles
Avogadro’s number
molar mass is the mass in grams of one mole of an element (g/mol)

13. Atoms, Molecules, and the Mole
use the formula of a compound to determine the molar mass
use molar mass to convert to moles (amount)
use molar mass to convert to molecules

14. 2.10 Describing Compound Formulas
Molecular composition
formula of compound
mass of each element per mole of compound
mass of each element relative to the total mass of the compound (mass percent)

15. Empirical and Molecular Formulas
convert mass percent to mass
convert mass of each element to moles
find the mole ratio of elements
the simplest, whole-number ratio is the empirical formula
If the molar mass is determined experimentally, then you can also figure out the molecular formula.

16. Practice Problems
The empirical formula of acetic acid is CH2O. If its molar mass is g/mol, what is the molecular formula of acetic acid?
Isoprene is a liquid compound that can be polymerized to form synthetic rubber. It is composed of 88.17% carbon and 11.83% hydrogen. Its molar mass is g/mol. What are its empirical and molecular formulas?

17. Practice Problems
Camphor is found in “camphor wood,” much prized for its wonderful odor. It is composed of 78.90% carbon and 10.59% hydrogen. The remainder is oxygen. What is its empirical formula?
Analysis shows that g of potassium metal combines with g of O2 gas to give a white solid having a formula of KxOy. What is the empirical formula of the compound?

18. Hydrated Compounds
Compounds in which molecules of water are associated with the ions of the compound are called hydrated compounds.
Copper (II) chloride dihydrate is CuCl2∙2H2O which is the same as CuCl2(H2O)2
anhydrous means a substance without water

19. Practice Problem
Hydrated nickel(II) chloride is a beautiful green, crystalline compound. When heated strongly, the compound is dehydrated. If g of NiCl2xH2O gives g of NiCl2 on heating, what is the value of x?

20. Mass Spectrometry
If a compound can be vaporized, the vapor can be passed through an electron beam where high energy electrons collide with the gas molecules. These collisions cause molecules to lose electrons and become positive ions. These ions usually fragment, and the mass spectrometer detects and records the masses of the different particles.

21. Mass Spectrum of Ethanol

22. Homework for Chapter 2
After reading sections 2.6 – 2.11, you should be able to do the following problems…
P. 95b-e (36-37,47,54-55,60-61,77,91,93)