1 chemistry writing formulas 2 chemical formulas and chemical compounds

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ChemistryChemistry

Writing FormulasWriting Formulas

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CHEMICAL CHEMICAL FORMULAS AND FORMULAS AND

CHEMICAL CHEMICAL COMPOUNDSCOMPOUNDS

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IONIC COVALENTBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

e- are transferred from metal to nonmetal

high

yes (solution or liquid)

yes

e- are shared between two nonmetals

low

no

usually not

MeltingPoint

crystal lattice true molecules

Types of BondsTypes of Bonds

Physical State solid liquid or gas

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Ionic Bonding - Crystal LatticeIonic Bonding - Crystal Lattice


The crystals are made up of alternating positive and negative ions.

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Covalent Bonding - True MoleculesCovalent Bonding - True Molecules


Diatomic Diatomic MoleculeMolecule

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“electron sea”

METALLICBond Formation

Type of Structure

Solubility in Water

Electrical Conductivity

OtherProperties

MeltingPoint


Physical State

e- are delocalized among metal atoms

very high

yes (any form)

no

malleable, ductile, lustrous

solid

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Metallic Bonding - “Electron Sea”Metallic Bonding - “Electron Sea”


The valence electrons move freely around the atoms

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Predicting Ionic Predicting Ionic ChargesCharges

Group 1Group 1::Lose 1 electron to form Lose 1 electron to form 1+1+ ions ions

HH++ LiLi++ NaNa++ KK++

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Group 2Group 2::Loses 2 electrons to form Loses 2 electrons to form 2+2+ ions ions

BeBe2+2+ MgMg2+2+ CaCa2+2+ SrSr2+2+ BaBa2+2+

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Predicting Ionic Predicting Ionic ChargesChargesGroup 13Group 13:: Loses 3 Loses 3

electrons to form electrons to form 3+3+ ions ions

BB3+3+ AlAl3+3+ GaGa3+3+

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Predicting Ionic Predicting Ionic ChargesChargesGroup 14Group 14:: Lose 4 Lose 4

electrons or gain electrons or gain 4 electrons4 electrons

C, Si and Ge, +4 and -4; Sn and Pb +4

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Group 15Group 15:: Gains 3 Gains 3 electrons to form electrons to form 3-3- ions ions

NN3-3-

PP3-3-

AsAs3-3-

Nitride

Phosphide

Arsenide

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Group 16Group 16:: Gains 2 Gains 2 electrons to form electrons to form 2-2- ions ions

OO2-2-

SS2-2-

SeSe2-2-

Oxide

Sulfide

Selenide

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Group 17Group 17:: Gains 1 Gains 1 electron to form electron to form 1-1- ions ions

FF1-1-

ClCl1-1-

BrBr1-1-Fluoride

Chloride

Bromide

II1-1- Iodide

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Group 18Group 18:: Stable Stable Noble gases Noble gases do do notnot form ions! form ions!

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VocabularyVocabulary

Chemical BondChemical Bond

electrical attraction between nuclei electrical attraction between nuclei and valence eand valence e-- of neighboring atoms of neighboring atoms that binds the atoms togetherthat binds the atoms together

bonds form in order to…bonds form in order to…decrease energydecrease energyincrease stabilityincrease stability

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BINARY IONIC BINARY IONIC COMPOUNDSCOMPOUNDS

BINARY - TWO ELEMENTS: A BINARY - TWO ELEMENTS: A METAL AND A NONMETALMETAL AND A NONMETAL

MOST ARE SALTSMOST ARE SALTS OTHER COMPOUNDS ARE OXIDESOTHER COMPOUNDS ARE OXIDES

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Writing Chemical Writing Chemical FormulasFormulas

We use the “criss cross” methodWe use the “criss cross” method Translate the names of the elements to Translate the names of the elements to

symbols.symbols. Use the periodic table to find the charges.Use the periodic table to find the charges. Find the charge on the positive ion, and Find the charge on the positive ion, and

write it above the symbol. Write the write it above the symbol. Write the charges small!charges small!

Find the charge on the negative ion, and Find the charge on the negative ion, and write it above the symbol. Write the write it above the symbol. Write the charges small!!charges small!!

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The The numbersnumbers, not the charges, , not the charges, determine the subscripts.determine the subscripts.

If the charges do not have the same If the charges do not have the same number, then you need subscripts.number, then you need subscripts.

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Example: potassium bromideExample: potassium bromide

Potassium is K, bromine is BrPotassium is K, bromine is Br

K+1 Br-1

KBrSince -1 and +1 = 0, the charges cancel each other out, and subscripts are not needed.

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Example: magnesium chlorideExample: magnesium chloride

Mg+2 Cl-1

The 2 from magnesium’s charge will become a subscript. We do not use a 1 for a subscript.

MgCl2

We need 2 chlorines for every one magnesium

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Example: lithium sulfideExample: lithium sulfide

Li+1 S-2

The 2 from sulfur’s charge will become a subscript. We do not use a 1 for a subscript.

Li2S

We need two lithium atoms for every one sulfur atom

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Example: aluminum oxideExample: aluminum oxide

Al+3 O-2

This time, the numbers are “criss crossed” in both directions. Each element will get a subscript.

Al2O3

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Check your subscripts!Check your subscripts!

Compounds do not have a charge. Compounds do not have a charge. They are zero. So, the charges on They are zero. So, the charges on the ions must equal zero. Check to the ions must equal zero. Check to be sure!be sure!

AlAl22OO33

(2 Al ions) (+3) = +6(2 Al ions) (+3) = +6 (3 O ions) (-2) = -6(3 O ions) (-2) = -6 +6 and -6 = 0+6 and -6 = 0

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You try these:You try these: magnesium magnesium

bromidebromide strontium oxidestrontium oxide aluminum aluminum

sulfidesulfide zinc iodidezinc iodide

AnswersAnswers MgBrMgBr22

SrOSrO AlAl22SS33

ZnIZnI22

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POLYATOMIC POLYATOMIC COMPOUNDSCOMPOUNDS

Contain three or more atomsContain three or more atoms Use the list on your blue sheet.Use the list on your blue sheet.

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Calcium Calcium carbonatecarbonateCaCa+2+2COCO33

-2 -2

Sodium sulfateSodium sulfate

NaNa+1+1SO4SO4-2-2

The 1 from Na is not used as a The 1 from Na is not used as a subscript.subscript.

CaCO3

Na2SO4

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Always check the charges and write them above the symbols! After you are comfortable with the charges, you may leave them off. If you have more than one polyatomic ion in a compound, you must enclose the ion in parenthesis, then use a subscript. No parenthesis if there is not a subscript!!!

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MORE FORMULASMORE FORMULAS

Magnesium Magnesium nitratenitrate

Mg+2 NO3-

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Mg(NOMg(NO33))22

You must put parenthesis around the NO3 ion because you have two of them.

Do not use parenthesis around single atoms

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More polyatomic More polyatomic compoundscompounds

Barium phosphateBarium phosphate

Ba+2 PO4-3 Ba3(PO4)2

Ammonium carbonate

(NH4)+1 CO3-2+1 -2 (NH4)2 CO3

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Writing formulasWriting formulas

Calcium carbonateCalcium carbonate

Sodium sulfateSodium sulfate

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MORE FORMULASMORE FORMULAS

Strontium hydroxideStrontium hydroxide This compound is tricky because you This compound is tricky because you

may forget to add parenthesis may forget to add parenthesis around the hydroxide ion.around the hydroxide ion.

Sr+2OH-1 Sr(OH)2

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REMEMBER TO:REMEMBER TO:

WRITE THE CORRECT SYMBOLWRITE THE CORRECT SYMBOL WRITE THE CORRECT CHARGE WRITE THE CORRECT CHARGE

ABOVE THE IONABOVE THE ION BRING DOWN THE NUMBER FOR BRING DOWN THE NUMBER FOR

THE SUBSCRIPT IF NEEDED.THE SUBSCRIPT IF NEEDED. REWRITE THE FORMULA REWRITE THE FORMULA

WITHOUT THE CHARGES.WITHOUT THE CHARGES.

1 chemistry writing formulas 2 chemical formulas and chemical compounds

Documents

charges small

atoms togetherbonds

sulfurs charge

magnesiums charge

lithium atoms

negative ions

neighboring atoms

positive ion