naming covalent compounds & their lewis dot structures

11 Mr. Shields Regents Chemistry U10 L03

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There are two conventions used for naming Binary Organic Compounds:

1) Common Name usage2) Stock System

Recall: We used the Stock System when we namedIonic compounds

- Example Cr(NO3)3 is named Chromium (III) Nitrate

For Covalently bonded compounds it works prettyMuch the same

Naming conventionsNaming conventions

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Rules for using the stock system to nameCovalent Compounds:

1)Place and Name the least electronegative element firstex: SO2 not O2S

2) Determine the Oxidation state of the 1st named elementex: SO2 S= +4

3) Use Roman Numerals to designate the oxidation numberex: SO2 is Sulfur (IV)

4) Ending for the More electronegative element is –ideex: SO2 is Sulfur (IV) Oxide

Stock SystemStock System

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Stock Name ProblemsStock Name Problems

Using Stock System nomenclature name the following:

CBr4

SO3

N2O5

N20

Carbon (IV) Bromide

Sulfur (VI) Oxide

Nitrogen (V) Oxide

Nitrogen (I) oxide

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Common Name SystemCommon Name System

In the Common naming system the following rulesApply:

1)Place and Name the least electronegative element first (just like in the stock system)

ex: PCl3 not Cl3P

2) Ending for the More electronegative element is –ide (again just like the stock system)

ex: Chlorine Chloride

3) Here’s the difference: Specify the NUMBER OF ATOMS as a prefix using the names in the following table…

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Common Covalent PrefixesCommon Covalent Prefixes

Atom name PrefixAtom name Prefix To designate To designate this # of atomsthis # of atoms

MonoMono 11

DiDi 22

TriTri 33

TetraTetra 44

PentaPenta 55

HexaHexa 66

HeptaHepta 77

OctaOcta 88

Ex: Si3N4 = Trisilicon Tetranitride

Whats the StockSystem name?

(N ox. # =-3)

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The prefix “Mono” isNot added to the 1st

Name of a compound

Ex: CO is

carbon monoxideNot

Monocarbon Monoxide

Also ->The “Fine Print”

Some other Rules:

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Common Name System ExceptionsCommon Name System Exceptions

Here are some Common Name exceptions dueto more familiar name usage:

NH3

O2

H2O

Ammonia not Nitrogen Trihydride

Oxygen not Dioxide or Dioxygen(same is true for other diatomics)

Water not Dihydrogen monoxide

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Common Name SystemCommon Name System

Using common nomenclature name the following:

CBr4

SO3

N2O5

P2S3

Carbon tetrabromide

Sulfur trioxide

Dinitrogen Pentoxide

DiPhosphorous Trisulfide

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Lewis Dot structures show how atoms are connected,Lewis Dot structures show how atoms are connected,And what bonds are present by indicating theAnd what bonds are present by indicating thePlacement of valence electronsPlacement of valence electrons

CH4

METHANE

Drawing Lewis Dot Structures

Let’s look at the rules for drawing these structuresLet’s look at the rules for drawing these structures

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Rules for Drawing Covalent Lewis Rules for Drawing Covalent Lewis Dot StructuresDot Structures

Rules:Rules:

1)1)Count the total number of valence electrons for all atomsCount the total number of valence electrons for all atoms

- CO- CO22 1C = 4 electrons 1C = 4 electrons + 2O= 12 electrons+ 2O= 12 electrons = 16 electrons= 16 electrons

2) Connect the atoms by single covalent bonds (make it2) Connect the atoms by single covalent bonds (make it symmetrical if possible)symmetrical if possible)

O – C – OO – C – O Remember a single line represents 2eRemember a single line represents 2e--

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Rules for Drawing Covalent Lewis Rules for Drawing Covalent Lewis Dot StructuresDot Structures

3) Subtract the single bond electrons from the total numberof electrons

- CO2 16 electrons – 4 = 12 electrons

4) Add remaining electrons symmetrically as lone pairs

. . ..

. . ..:O – C – O:

DO THE TEST: DOES EVERY ATOM HAVE AN OCTET?

- YES You’re Done- NO Move lone pairs into bonding positions

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. . ..

. . ..

:O – C – O:

. . ..

. .

:O – C = O:

TEST: Do all atoms have an octet?

NO - Move lone pair into bonding positionfrom other atom

. . ..

. .

:O – C = O:

. . ..:O = C = O:

TEST: Do all atoms have an octet?

YES - THEN YOU’RE DONE !

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Try the FollowingTry the Following

Draw the Lewis dot structure for N2H2

1)Count the total number of valence electrons for all atoms

- N2H2 2N = 10 electrons + 2H = 2 electrons = 12 electrons

2) Connect the atoms by single covalent bonds (make it symmetrical if possible)

H – N – N - H Symmetrical and H can only share 2 electrons

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Try the followingTry the following

3) Subtract the single bond electrons from the total numberof electrons

H – N – N - H 12 electrons – 6 = 6 electrons

4) Add remaining electrons as lone pairs

TEST: DOES EVERY ATOM HAVE AN OCTET?

- NO? Move lone pairs into bonding positions

H - N – N - H

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RETEST: Do all atoms have an octet?

YES – THEN YOU’RE DONE !

.. .. ..H - N – N - H ..

.. H - N = N - H

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Try This one:

Draw the Lewis Dot Structure for SO3

.. ..:O:S::O:

.. ..

:O:

..