naming compounds and writing formulas

Naming Naming Compounds and Compounds and

Writing Writing FormulasFormulas

Unit 7, Part B

Valence Electrons as Valence Electrons as Electron DotsElectron DotsRemember that the number of

valence electrons is a periodic trend! H He

Li• •Be• •B• C

N O F Ne

•••

•

•

••

• ••

•••••

••

• •• •••• ••

•• •••

• ••

Atoms vs. Molecules vs. Atoms vs. Molecules vs. IonsIonsRemember how to tell these apart!

Atom: Single particle, pure elementExample: Fe, C, Mg

Molecule: Two or more nonmetal particles covalently bonded together

Example: N2, CO2, H2O

Ion: Charged atom or moleculeExample: Cl-1, Zn+2, SO4

-2

Group I: Binary Ionic Group I: Binary Ionic Compounds with Metals of Compounds with Metals of Fixed ChargeFixed Charge

This includes the metals from groups 1A (alkali metals are +1), 2A (alkaline earth metals are always +2), Al+3, Zn+2, and Ag+1.

These metals will always have the same charge.

Binary Ionic Compound Binary Ionic Compound FormulasFormulasRemember that in an ionic

compound the charges must balance so that the compound is neutral

(The charge of the first atom multiplied by the subscript) ++ (the charge of the second atom multiplied by its subscript) mustmust = 0= 0

NaNa++ + Cl + Cl-- NaClNaCl

Binary Ionic Compound w/ Binary Ionic Compound w/ Fixed ChargeFixed ChargeNaming

1. Write the name of the metal 2. Write the root of nonmetal + -ide

suffix

Formulas1. Write the symbols for each element and

their charges from the periodic table.2.Crisscross the charges to get the

subscripts.3.Reduce to lowest terms

Binary Ionic Compound Binary Ionic Compound Formulas Formulas The The Long WayLong WayFind the least common multiple (LCM)

of the ions’ chargesMultiply the charges by whatever

number is needed to equal the LCMThat number will be your subscriptsExample: calcium phosphide

Ca is Ca is +2+2P is -3P is -3

Multiples of 2: 2 4 6 8 10 12 etc.Multiples of 3: 3 6 9 12 15 18 etc. For Ca +2 x

____ = +6For P -3 x ____ = -6

3322 Ca3P2

Binary Ionic Compound Binary Ionic Compound Formulas Formulas ShortcutShortcutCriss-cross method!Naming

◦ Write the name of the metal ◦Write the root of nonmetal + -ide suffix

Crisscross the charges to get the subscripts.Reduce to lowest termsCalcium phosphide

Ca

P

22++

3-3-

33 22Ca3P2

Note: You do not have to write a subscript of 1, just write the symbol.

Also, reduce common numbers: Instead of Mg2O2, you just use MgO

Note: You do not have to write a subscript of 1, just write the symbol.

Also, reduce common numbers: Instead of Mg2O2, you just use MgO

Let’s try a few…Let’s try a few…sodium chloridebarium bromidealuminum oxide

Na+1, Cl-1, so NaClBa+2, Br-1, so BaBr2

Al+3, O-2, so Al2O3

Remember, 1 is understood, so omit it!

Naming Binary Ionic Naming Binary Ionic CompoundsCompounds

1. The positive ion (cation) goes first, and the negative ion (anion) goes second.

2. Use the name of the cation + the root name of the anion + the suffix –ide

Example: BaF2Ba is bariumF is fluorine barium barium

fluoridefluoride

Let’s try a few…Let’s try a few…Li3NCaF2

SrI2

Group 2: Binary Ionic Group 2: Binary Ionic Compounds with Metals That Compounds with Metals That Vary in ChargeVary in ChargeThese compounds use all the rest

of the metals including transition metals.

The charge on these metals could be anything between +1 and +7, depending on the metal, but two charges are most common for each.

Group 2: Ionic Compound w/ Group 2: Ionic Compound w/ Transition MetalsTransition Metals

Naming1.Write name of metal and its charge in Roman

Numerals.2.Write name of polyatomic ion, or nonmetal + -

ide.

Formulas1. Write symbols for positive metal w/ charge +

nonmetal or polyatomic ion w/ charge.2.Crisscross charges for subscripts. If you need a

subscript on a polyatomic ion, put parentheses around it first.

3.Reduce subscripts to lowest terms.

Formulas for Group 2Formulas for Group 2

Criss-cross method1.Write the charges for each ion.

The metal charge is given in Roman Numerals!

2.Criss-cross the charges down as subscripts and reduce to lowest terms

Example: Copper (II) chloride

CuCl2

Let’s try a few!Let’s try a few!

1. Lead (IV) oxide2. Iron (II) sulfide3. Iron (III) sulfide

Naming Group 2 Naming Group 2 CompoundsCompounds1. Name the metal first, and give

its charge in Roman Numerals in parentheses. You can reverse criss-cross, or use the nonmetal charge to balance the positive.

2. Name the nonmetal root + -ide suffix.

Example: CrF2

Chromium (II) fluoride

Remember!! The Roman Numeral is NOT the subscript!

Let’s try some!Let’s try some!

1. CuBr2

2. CuBr3. SnO2

Polyatomic IonsPolyatomic IonsMany ionic compounds contain

polyatomic ionspolyatomic ions, which are ions made up of more than one atom.

The charge given to the polyatomic ion applies to the entire group of atoms.

Note that ammonium is

the only positive

polyatomic ion (cation).

Group 3: Ionic Compounds Group 3: Ionic Compounds w/ Polyatomic Ionsw/ Polyatomic IonsNaming

1. Write name of metal or + polyatomic ion, use RN as needed.

2. Write name of negative polyatomic ion or nonmetal + -ide.

Formulas1. Write symbols for positive ions and

negative ions w/ charges.2.Crisscross charges for subscripts. If you

need a subscript on a polyatomic ion, put parentheses around it first.

3.Reduce subscripts to lowest terms.

Group 3: Writing Formulas Group 3: Writing Formulas with Polyatomic Ionswith Polyatomic IonsFollow the same rules as binary

ionic compoundsTreat the polyatomic ion as a

single unit; don’t change its subscripts

If more than one polyatomic ion is needed, place parentheses around it and write the subscript outside of the parentheses.

Example: 2 carbonates is (CO(CO332-2-))22

Writing Formulas with Writing Formulas with Polyatomic IonsPolyatomic IonsExample: magnesium chlorate

magnesium is Mg charge is 2+chlorate is ClO3

-

charge is 1-

Mg

ClO3

22++

--11 22Mg(ClO3)2

Practice!Practice!sodium nitratecalcium chloratealuminum carbonatepotassium chromate

Group 3: Naming Group 3: Naming CompoundsCompounds1. Name the metal or positive

polyatomic ion. Use Roman Numeral if needed for metal of varying charge.

2. Name the negative polyatomic ion, or nonmetal root + -ide suffix.

Example: Ca3(PO4)2

Calcium phosphate Example: Cu(NO3)2

Copper (II) nitrate

Practice!Practice!

1. CaSO4

2. Al(OH)3

3. Pb(C2H3O2)4

Group 4: Binary Covalent Group 4: Binary Covalent CompoundsCompoundsNaming1. Write the name of the first nonmetal.

Put a prefix on it if it has a subscript.2. Write a prefix for the second nonmetal

+ root of nonmetal + -ide.

Formulas1.Write the symbols of each

nonmetal.2.Use the prefixes to determine the

subscript. Never use charges!!

Group 4: Naming Binary Group 4: Naming Binary Covalent CompoundsCovalent CompoundsRules are similar to binary ionic

compounds◦ Use the name of the first element◦ Use the root of the name of the 2nd element,

plus the suffix –ideBut add prefixes to indicate the number of

atoms in the compound

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

PREFIXESPREFIXES

Note: You do not have to say “mono-” for the first element. Example: CO is “carbon monoxide.”

Note: You do not have to say “mono-” for the first element. Example: CO is “carbon monoxide.”

Naming Binary Covalent Naming Binary Covalent CompoundsCompounds

NO2

N2O5

Let’s try

Let’s try

a few…

a few…

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta

8 octa-

9 nona-

10 deca-

PREFIXESPREFIXES

Naming Acids - TypesNaming Acids - TypesBinary acidBinary acid: contains hydrogen

and one other element◦Examples: HCl, HBr

OxyacidOxyacid: contains hydrogen and an oxyanion, which is a polyatomic ion that contains oxygen◦Examples: H2SO4, HNO3

Naming Binary AcidsNaming Binary AcidsUse the prefix hydro-hydro- to name the

hydrogen part of the compoundUse the root of the 2nd element

plus the suffix –ic–icAdd the word acidacid

Example: HBr is hydrobromic acid

Practice Naming Binary Practice Naming Binary AcidsAcidsHFHClHCN (tricky!)

◦Some “binary” acids contain polyatomic ions

◦As long as there is NO OXYGEN, follow the regular binary acid rules Hydro-Hydro- + (root of ion) + -ic-ic + acidacid So HCN would be…So HCN would be…

Hydrocyanic acidHydrocyanic acid

Naming OxyacidsNaming OxyacidsDo NOT put hydro-Identify the polyatomic anion presentUse the root of the anion’s nameChange the suffix

◦-ate –ic–ic◦-ite –ous –ous

Add the word acid

Example: H2SO4 contains sulfate…

sulfuric acidsulfuric acid

Practice with OxyacidsPractice with OxyacidsH3PO4

HNO2

Sulfurous acidNitric acid