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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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Guide to Naming Covalent Compounds with Two Nonmetals

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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

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Try these on your own! ClF

ClF5

BCl3SF6

Cl2O

IF7

NI3P4O10

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

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Practice Writing Formulas

Phosphorus Trioxide

Dinitrogen Pentacarbide

Tellurium Noniodide

Carbon Monoxide

Selenium Heptaflouride

Tetraphosphorous Decoxide

Arsenic Hexabromide

Silicon Dichloride

Check your answers

S2F10

OF2

N2O3

P4S7

CS2

XeF2

ICl3

PO3

N2C5

TeI9

SeF7

AsBr6

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