Part III: NAMING BINARY COVALENT COMPOUNDS

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 Nonmetals 4

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- 9 = nona- 5 = penta- 10 = 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 • The complete name is disulfur heptoxide (a in hepta- is dropped before the vowel o in oxide) • 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

13. Another Example The complete name is tetraphosphorus trisulfide • 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

14. A Few More Examples

15. 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 • PO3 • N2C5 • TeI9 • 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