1. Unit 1 – Intro to Chemistry: Molecules and Compounds
Unit 2: Molecules and Compounds
Unit 1 – Intro to Chemistry: Molecules and Compounds

2. Chemical Formula Indicates: Ex: H2O
Unit 2: Molecules and Compounds
Chemical Formula
Indicates:
The elements present
The relative number of atoms of each element
Ex: H2O
The symbols H and O indicate the presence of hydrogen and oxygen, while the number 2 indicates that there are 2 atoms of hydrogen per one atom of oxygen
Note: You do not need to write the number “1” if there is only one molecule of an element. If there is no number beside the element, it is assumed there is only one molecule of that element.

3. How do Atoms Bond? There are two basic types of bonding: Ionic Bonding
Unit 2: Molecules and Compounds
How do Atoms Bond?
There are two basic types of bonding:
Ionic Bonding
Covalent Bonding

4. Ionic Bonding Attraction between two oppositely charged ions
Unit 2: Molecules and Compounds
Ionic Bonding
Attraction between two oppositely charged ions
Usually between a metal and a nonmetal
Atoms of metals tend to lose one or more electrons (Cations), whereas atoms of non metals tend to gain one or more electrons (Anions)

5. Unit 2: Molecules and Compounds
Ionic Bonding
Ex: Na+ and Cl- are attracted to each other because they are oppositely charged ions; these two ions give us NaCl (table salt)

6. Ionic Bonding Continued
Unit 2: Molecules and Compounds
Ionic Bonding Continued
The chemical formula for an ionically bonded molecule is called a Formula Unit, which is the smallest electrically neutral collection of ions
Ex: NaCl, MgCl2, Li2O, H3PO4 all represent formula units

7. How do we know the Charges of Ions?
Unit 2: Molecules and Compounds
How do we know the Charges of Ions?
Remember how elements will lose or gain an electron to become more stable….group 1 elements lose one electron to give them a charge of +1, group 6 gains two electrons to have a charge of -2.
Periodic Group
Charge
Examples 1 +1
H+, Li+, Na+, K+ 2 +2
Be2+, Mg2+, Ca2+ 5 -3
N3-, P3- 6 -2
O2-, S2- 7 -1
F-, Cl-, Br-, I-

8. Ionic Bonding continued
Unit 2: Molecules and Compounds
Ionic Bonding continued
Monatomic Ion: a single ionized atom
Ex: Na+, Cl-, Mg2+, Fe2+, Fe3+
Polyatomic Ion: made up of two or more atoms joined by covalent bonds
Ex: NO3-, NH4+
* Notice how some transition metals can have more than one charge *

9. Unit 2: Molecules and Compounds
Oxidation States
Oxidation state is the number of electrons that an atom loses or gains when joining with other atoms in compounds (same as charge of ion)
When added together, the formula unit of a compound should be 0!
Ex: NaCl Na+ is in an oxidation state of +1 and Cl- is in an oxidation state of (-1) = 0

10. Unit 2: Molecules and Compounds
Naming Compounds
Compounds formed by carbon and hydrogen or carbon and hydrogen together with oxygen, nitrogen and a few other elements are organic compounds
All other compounds that do not fit this description are inorganic compounds

11. Name and Formulas of Inorganic Compounds: Binary Compounds
Unit 2: Molecules and Compounds
Name and Formulas of Inorganic Compounds: Binary Compounds
Binary compounds: those formed between two elements
To name a binary compound that consists of a metal and nonmetal:
Write the unmodified name of the metal
Then write the name of the nonmetal, modified to end in “ide”
Examples NaCl = Sodium Chloride MgI2 = Magnesium Iodide Al2O3 = Aluminum Oxide
Ionic Compounds must be electrically neutral (total charge of the ions in a formula unit must be zero)

12. Binary compounds: Metal/Nonmetal
Unit 2: Molecules and Compounds
Binary compounds: Metal/Nonmetal
Transition metals form several ions, for example, iron forms two common ions, Fe2+ and Fe3+
Use roman numerals to indicate which one was used (Fe2+ = Iron(II) and Fe3+ = Iron (III) )
Ex: Fe2S3 = Iron(III) Sulfide
Note: we looked at the number of S atoms to get Iron(III)
Fe2S3 is electrically neutral 2(3) + 3(-2) = 0

13. Binary compounds: Metal/Nonmetal
Unit 2: Molecules and Compounds
Binary compounds: Metal/Nonmetal
Old system used the words ferrous/ferric instead of Fe2+ and Fe3+
Another example: Cu2O is Copper(I) Oxide or Cuprous oxide, CuO is Copper (II) Oxide or Cupric Oxide.

14. Binary compounds: Polyatomic Ions
Unit 2: Molecules and Compounds
Binary compounds: Polyatomic Ions
Name of the first element and the name of the polyatomic ion
Do not need to change the name to end in “ide”, just keep the name as is.
Ex: NaNO3 is Sodium Nitrate NOT Sodium Nitride

15. Inorganic Compounds: Hydrates
Unit 2: Molecules and Compounds
Inorganic Compounds: Hydrates
Each formula unit of the compound has associated with it a certain number of water molecules
To name: write down compound name according to nomenclature rules and then add “prefix” hydrate.
Example: CoCl2●6H2O Cobalt(II) chloride hexahydrate

16. Summary of Naming Unit 2: Molecules and Compounds Inorganic
2 Non Metals
Prefixes = # of atoms (1=mono, 2=di, etc.)
Last element ends in “ide”
Metal/Nonmetal
Monoatomic
Polyatomic
No Different Ending
Hydrate
Follow other rules, add “prefix”hydrate
Summary of Naming

17. Binary Compounds: Two Nonmetals
Unit 2: Molecules and Compounds
Binary Compounds: Two Nonmetals
Write the element with the positive oxidation state first: HCl not ClH
Second element still ends in “ide” but need to use prefixes: Mono = 1 Tetra = Di = 2 Penta = Tri = 3 Hexa = 6
Examples: SO2 = Sulfur Dioxide B2Br4 = Diboron tetrabromide
* Need to know these prefixes *

18. Binary Compounds: Two Nonmetals
Unit 2: Molecules and Compounds
Binary Compounds: Two Nonmetals
More examples:
NO = Nitrogen Monoxide (Note that it isn’t mononitrogen monoxide, mono is never used in the first named element)
H2O = Dihydrogen monoxide (water)

19. Ionic vs. Covalent Bonding
Unit 2: Molecules and Compounds
Ionic vs. Covalent Bonding
Ionic: Transfer of electron(s) from one atom to another. Example is Sodium Chloride, NaCl
Covalent: The atoms share electrons. Example is Methane, CH4 H H C H H Cl Na H H C H C H Cl Na + - H

20. Unit 2: Molecules and Compounds

21. Unit 2: Molecules and Compounds

22. So what is a Compound?
Compounds are pure substances and not mixtures (Examples: Water (H2O), Carbon Dioxide (CO2) )
Compounds are made of atoms of two or more elements