Part III: NAMING BINARY COVALENT COMPOUNDS
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Transcript of 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?
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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.
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The first word corresponds to the first element in the formula – as it appears on the periodic table
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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
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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-
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Prefixes
1 =mono- 6 = hexa-
2 = di- 7 = hepta-
3 = tri- 8 = octa-
4 = tetra- 9 = nona-
5 = penta- 10 = deca-
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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
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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)
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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
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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
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
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Practice Writing Formulas
Phosphorus Trioxide
Dinitrogen Pentacarbide
Tellurium Noniodide
Carbon Monoxide
Selenium Heptaflouride
Tetraphosphorous Decoxide
Arsenic Hexabromide
Silicon Dichloride
Naming Molecular Compound Answers
1. Carbon dioxide2. Carbon monoxide3. Sulfur dioxide4. Sulfur trioxide5. Dinitrogen monoxide6. Nitrogen monoxide7. Dinitrogen trioxide8. Nitrogen dioxide9. Dinitrogen tetroxide10. Dinitrogen pentoxide
11. Phosphorous trichloride12. Phosphorous pentachloride13. Nitrogen trihydride14. Sulfur hexachloride15. Diphosphourous pentoxide16. Carbon tetrachloride17. Silicon dioxide18. Carbon disulfide19. Oxygen difluoride20. Phosphorous tribromide