1. Part III: NAMING BINARY COVALENT COMPOUNDS

2. Essential Questions:
How can we decipher the name of covalent compounds from their formulas?
And how can we figure out the formulas from their names?

3. Naming Covalent Compounds
Note: We are just dealing with binary compounds – which are compounds with only two types of atoms.
They have two word names.

4. Guide to Naming Covalent Compounds with Two Nonmetals4

5. The first word corresponds to the first element in the formula – as it appears on the periodic table

6. The second word corresponds to the second element in the formula
Use the root of its name from the periodic table and add the suffix –ide

7. For the first element:
Remember that the # of atoms is given by a subscript
ONLY add a prefix if there is more than one atom. (never write mono- on the first element)

8. For the second element:
ALWAYS add a prefix to the word to tell how many are present (even if there’s only one)
Drop “o” or “a” at the end of a prefix when the word following the prefix is oxide (monoxide, pentoxide) but do not drop “i”
Never drop anything at the end of a prefix when the word following the prefix is iodide

9. Roots of Nonmetals
H = hydr- C = carb- N = nitr- P = phosph- O = ox- S = sulf- Se = selen- F = fluor- Cl = chlor- Br = brom- I = iod-

10. Prefixes 1 =mono- 6 = hexa- 2 = di- 7 = hepta- 3 = tri- 8 = octa-
4 = tetra = nona-
5 = penta = deca-

11. Exceptions to the Rule
Some important exceptions to this naming scheme occur because the compounds were originally named before the methodical naming scheme above became widespread. Today, these names are so common that they're officially recognized:
H2O = water
NH3 = ammonia
CH4 = methane
Many others, particularly for organic molecules and acids

12. Example Name the molecular compound that has the formula S2O7
There are 2 sulfur atoms, so add the prefix di-
The first element is named first, using the unchanged element name: S = sulfur
There are 7 oxygen atoms, so add the prefix hepta-
The second element’s root is then written with the suffix -ide: O = ox- plus -ide = oxide
The complete name is disulfur heptoxide (a in hepta- is dropped before the vowel o in oxide)

13. tetraphosphorus trisulfide
Another Example
Name the molecular compound that has the formula P4S3
There are 4 phosphorus atoms, so add the prefix tetra-
The first element is named first, using the unchanged element name: P = phosphorus
There are 3 sulfur atoms, so add the prefix tri-
The second element’s root is then written with the suffix -ide: S = sulf- plus -ide = sulfide
The complete name is
tetraphosphorus trisulfide

14. A Few More Examples
P2O5
diphosphorus pentoxide, two phosphorus atoms and five oxygen atoms
 CO
carbon monoxide (need the "mono-" because there's only one oxygen atom)
CF4
carbon tetrafluoride, because there's one carbon atom and four fluorine atoms

15. ClF ClF5 BCl3 SF6 Cl2O IF7 NI3 P4O10 B5H9
Try these on your own!
ClF ClF5 BCl3 SF6 Cl2O IF7 NI3 P4O10 B5H9

16. Check your answers ClF – chlorine monofluoride
ClF5 – chlorine pentafluoride
BCl3 – boron trichloride
SF6 – sulfur hexafluoride
Cl2O – dichlorine monoxide
IF7 – iodine heptafluoride
NI3 – nitrogen triiodine
P4O10 – tetraphosphorous decoxide
B5H9 – pentaboron nonahydride

17. Practice Writing Formulas
Phosphorus Trioxide Dinitrogen Pentacarbide Tellurium Noniodide Carbon Monoxide Selenium Heptaflouride Tetraphosphorous Decoxide Arsenic Hexabromide Silicon Dichloride

18. Check your answers ICl3 S2F10 PO3 OF2 N2O3 N2C5 P4S7 TeI9 CS2 SeF7
AsBr6
S2F10
OF2
N2O3
P4S7
CS2
XeF2

19. Naming Molecular Compound Answers
Phosphorous trichloride
Phosphorous pentachloride
Nitrogen trihydride
Sulfur hexachloride
Diphosphourous pentoxide
Carbon tetrachloride
Silicon dioxide
Carbon disulfide
Oxygen difluoride
Phosphorous tribromide
Carbon dioxide
Carbon monoxide
Sulfur dioxide
Sulfur trioxide
Dinitrogen monoxide
Nitrogen monoxide
Dinitrogen trioxide
Nitrogen dioxide
Dinitrogen tetroxide
Dinitrogen pentoxide