Part III: NAMING BINARY COVALENT COMPOUNDS

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?

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.

Guide to Naming Covalent Compounds with Two Nonmetals 4

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

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

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)

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

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-

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

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

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)

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

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

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

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

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

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

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