Writing and Naming

Binary Compounds & Hydrates

You will need:

A periodic table

A list of common polyatomic ions

Patience and understanding

Generic Chemical Formulas

MgCl2

Chemical symbols

Subscript

Binary Compounds

1. Two elements chemically bonded

2. An element and a polyatomic ion chemically bonded

3. Two polyatomic ions chemically bonded

A chemical compound consisting of two parts, a CATION (+) and an ANION (-)

Examples:

Binary Compounds

Have two parts

Left side is the cation

Positively charged

Right side is the anion

Negatively charged

MgCl2

Hydrates

A hydrate is a binary compound that has water attached to its ions and the water is a PART of the chemical formula.

Naming hydrates uses terms that indicate the number of water molecules.

11 monomono

22 didi

33 tritri

44 tetratetra

55 pentapenta

66 hexahexa

77 heptahepta

88 octaocta

99 nonanona

1010 decadeca

Hydrates

CaSO4 • 2 H2O Calcium sulfate dihydrate

CuSO4 • 5 H2O

AlO3 • 3 H2O Aluminum oxide trihydrate

Copper (II) sulfate pentahydrate

Binary compound

Binary compound

Binary compound

Writing Binary Formulas

6 Steps

1. Write chemical symbols for cation and anion

2. Add cation and anion oxidation numbers as superscripts

3. Check to see if oxidation numbers add to zero

4. If yes, leave as written

5. If no, make oxidation numbers subscripts

6. Check for lowest whole number ratio

Writing Binary Formulas

Write the formula for sodium chloride.

Na Cl

1 2 3

+ -

4Write chemical symbols for the cation and anionAdd cation and anion oxidation numbers as superscripts

Check to see if oxidation numbers add to zero

If yes, leave as written

Writing Binary Formulas

Write the formula for magnesium nitride

Mg N

1 2 3 4 5

+2 -3

23

Writing Binary Formulas

Write the formula for hydrogen carbonate

H CO3

1 2 3 4 5

+ -2

2

Writing Binary Formulas

Write the formula for magnesium phosphate

Mg PO4

1 2 3 4 5

+2 -3

23( )

Writing Binary Formulas

For transition metals the oxidation number is given in parentheses, In Roman numerals.

Write the formula for iron (III) oxide.

Fe +3 O -2 Fe2 O3

Writing Binary Formulas

For hydrates, that is, binary compounds with water (hydrate) attached:

nickel (II) sulfate hexahydrate

a. Write the formula of the binary compound (first part) using rules 1-4:

NiSO4

b. Insert a “raised dot” after the binary compound:

NiSO4 ●

c. Use name prefix to note the number of water molecules (hydrates):

NiSO4 ● 6 H2O

Polyatomic Ions (learn these)Table 4 Page 619

NameName FormulaFormula

AmmoniumAmmonium NHNH44++

AcetateAcetate CC22HH33OO22--

ChlorateChlorate ClOClO33--

HydroxideHydroxide OHOH--

NitrateNitrate NONO33--

CarbonateCarbonate COCO332-2-

SulfateSulfate SOSO442-2-

PhosphatePhosphate POPO443-3-

More Polyatomic Ions

(learn these, too)

NameName FormulaFormula

Hydrogen carbonateHydrogen carbonate

(bicarbonate)(bicarbonate) HCOHCO33

--

Nitrite Nitrite NONO22--

PermanganatePermanganate MnOMnO44--

SulfiteSulfite SOSO332-2-

A quick review of hydrates.

Naming Binary Formulas

Binary Compound = CATION + ANION

First: Get a periodic table and table of common polyatomic ions

Next: Determine the cation and anion in the compound

Then: Note the cation and apply the 5 naming rules IN ORDER

Naming Binary Formulas

5 Rules that begin with the location or kind of the CATION

Rule 1. For elements in the first two columns of the periodic table

Rule 2. For elements from group 3 up to the staircase

Rule 3. For elements to the right (above) the staircase

Rule 4. For CATIONS that are polyatomic ions

Rule 5. For hydrates

Naming Binary Formulas – Rule 1

For cations (elements) in the first two columns of the periodic

table:

MgCl2 LiOH

a. Cation: Write the name of the element as the first part of the compound:

magnesium lithium

b. Anion: Write the name of the element with an ide ending:

magnesium chloride

c. Anion: Write the name of the polyatomic ion:

lithium hydroxide

or

Naming Binary Formulas – Rule 2

For cations (elements) from the third group of the periodic table up to the “staircase”

FeCl2 Cu2SO4

a. Cation: Name of element with Roman Numeral to show oxidation number:

iron (II) copper (I)

b. Anion: Name the element with an ide ending:

iron (II) chloride

c. Anion: Name the polyatomic ion:

copper (I) sulfate

or

Exceptions to rule:

Ag+1 Zn+2

Cd+2 Al+3

(Use Rule 1)

Naming Binary Formulas – Rule 3

For cations (elements) to the right (above) the “staircase”

CO2 CO N4S3

a. Count the “number” of each element. (C-1, O-2 C-1, O-1 N-4, S-3)

b. Use prefixes (mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca) to indicate the number of each atom present.

b. Do not use “mono” if there is only one of the first element in the compound.

c. CO2 N4S3

CARBON DIOXIDE TETRANITROGEN TRISULFIDE

CARBON MONOXIDECO

Naming Binary Formulas – Rule 4

For cations that are polyatomic ions:

NH4Cl NH4OH

a. Cation: Name the polyatomic ion:

ammonium ammonium

b. Anion: Name the element with an ide ending:

ammonium chloride

c. Anion: Name the polyatomic ion:

ammonium hydroxide

or

Naming Binary Formulas – Rule 5

For hydrates, that is, binary compounds with water (hydrate) attached:

NiSO4● 6 H2O

a. Name of the binary compound (first part) using rules 1-4:

nickel (II) sulfate

b. Note the number of water molecules (hydrates) by using prefixes:

nickel (II) sulfate hexahydrate

Rest stop!

Inhale and breathe easy!

The next group of slides goes into some detail about oxidation numbers in covalent compounds and in polyatomic ions. For this presentation, a periodic table that shows electronegativities is

most helpful.

Covalent CompoundsCovalent CompoundsExample: phosphate ion

P O43-

Since oxygen is the more electronegative element, it will

have its normal oxidation number.

-23.52.1

Polyatomic ion with a charge = -3

Electronegativity:

Covalent CompoundsCovalent CompoundsExample:

P O43-

-2

The phosphate ion has a charge of negative three, so the

oxidation numbers must add up to the total charge of the ion.

+5+ 5

- 8

- 3

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Ca SO4

This is an ionic compound, so the charge of the metal cation is its

oxidation number

+2

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Ca SO4

The anion is a polyatomic ion, sulfate, and the charge of sulfate is negative two. So the oxidation

numbers of sulfur and oxygen must add to -2

+2

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Ca SO4

Oxygen is the more electronegative of the two, so it

keeps its normal oxidation number.

+2 -23.52.5

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Ca SO4

Sulfur and the four oxygen atoms must add to negative two (the charge of the sulfate anion).

+2 -2+6

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Pb(OH)4This is an ionic compound, so the charge of the metal cation is its oxidation number. But this is a transition metal, so we cannot know it from its position on the

periodic table.

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Pb(OH)4But the anion, the hydroxide ion, carries a charge of negative one. All four hydroxides are negative one, but since the compound is neutral, the oxidation number of

lead must balance it out.

+4 -1

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Pb(OH)4Within the anion, oxygen is the more electronegative of the two elements, and keeps its normal

oxidation number.

+4 -2

3.5 2.1

Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:

Pb(OH)4Within the hydroxide ion, the

oxygen and hydrogen must add to the charge of the ion, -1

+4 -2 +1