Part III NAMING BINARY COVALENT COMPOUNDS 1 Essential

Part III: NAMING BINARY COVALENT COMPOUNDS 1

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

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. 3

Guide to Naming Covalent Compounds with Two Nonmetals 4 4

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

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

n For the first element: q q 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)

n For the second element: q q q 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

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

Prefixes 1 =mono 2 = di 3 = tri 4 = tetra 5 = penta- 6 = hexa 7 = hepta 8 = octa 9 = nona 10 = deca- 10

Exceptions to the Rule n 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: q q H 2 O = water NH 3 = ammonia CH 4 = methane Many others, particularly for organic molecules and acids 11

Example n Name the molecular compound that has the formula S 2 O 7 q q 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 n. The complete name is disulfur heptoxide (a in hepta- is dropped before the vowel o in oxide) 12

Another Example n Name the molecular compound that has the formula P 4 S 3 q q 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 13

A Few More Examples P 2 O 5 CO CF 4 diphosphorus pentoxide, two phosphorus atoms and five oxygen atoms carbon monoxide (need the "mono-" because there's only one oxygen atom) carbon tetrafluoride, because there's one carbon atom and four fluorine atoms 14

Try these on your own! Cl. F 5 BCl 3 SF 6 Cl 2 O IF 7 NI 3 P 4 O 10 B 5 H 9 15

Check your answers Cl. F – chlorine monofluoride Cl. F 5 – chlorine pentafluoride BCl 3 – boron trichloride SF 6 – sulfur hexafluoride Cl 2 O – dichlorine monoxide IF 7 – iodine heptafluoride NI 3 – nitrogen triiodine P 4 O 10 – tetraphosphorous decoxide B 5 H 9 – pentaboron nonahydride

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

Check your answers S 2 F 10 n OF 2 n N 2 O 3 n P 4 S 7 n CS 2 n Xe. F 2 n n ICl 3 n PO 3 n N 2 C 5 n Te. I 9 n Se. F 7 n As. Br 6

Naming Molecular Compound Answers 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Carbon dioxide Carbon monoxide Sulfur dioxide Sulfur trioxide Dinitrogen monoxide Nitrogen monoxide Dinitrogen trioxide Nitrogen dioxide Dinitrogen tetroxide Dinitrogen pentoxide 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. Phosphorous trichloride Phosphorous pentachloride Nitrogen trihydride Sulfur hexachloride Diphosphourous pentoxide Carbon tetrachloride Silicon dioxide Carbon disulfide Oxygen difluoride Phosphorous