2Essential Questions:How can we decipher the name of covalent compounds from their formulas?And how can we figure out the formulas from their names?
3Naming Covalent Compounds Note: We are just dealing with binary compounds – which are compounds with only two types of atoms.They have two word names.
4Guide to Naming Covalent Compounds with Two Nonmetals 4
5The first word corresponds to the first element in the formula – as it appears on the periodic table
6The 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
7For the first element:Remember that the # of atoms is given by a subscriptONLY add a prefix if there is more than one atom. (never write mono- on the first element)
8For 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
9Roots of NonmetalsH = hydr- C = carb- N = nitr- P = phosph- O = ox- S = sulf- Se = selen- F = fluor- Cl = chlor- Br = brom- I = iod-
11Exceptions to the RuleSome 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 = waterNH3 = ammoniaCH4 = methaneMany others, particularly for organic molecules and acids
12Example 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 = sulfurThere 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 = oxideThe complete name is disulfur heptoxide (a in hepta- is dropped before the vowel o in oxide)
13tetraphosphorus trisulfide Another ExampleName the molecular compound that has the formula P4S3There are 4 phosphorus atoms, so add the prefix tetra-The first element is named first, using the unchanged element name: P = phosphorusThere 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 = sulfideThe complete name istetraphosphorus trisulfide
14A Few More ExamplesP2O5diphosphorus pentoxide, two phosphorus atoms and five oxygen atoms COcarbon monoxide (need the "mono-" because there's only one oxygen atom)CF4carbon tetrafluoride, because there's one carbon atom and four fluorine atoms
15ClF ClF5 BCl3 SF6 Cl2O IF7 NI3 P4O10 B5H9 Try these on your own!ClF ClF5 BCl3 SF6 Cl2O IF7 NI3 P4O10 B5H9