Chemical Formulas and Names for Ionic Compounds

Terminology Review:

A chemical formula uses chemical symbols to represent a particular compound.

Compound – 2 or more different elements chemically bonded together in a fixed proportion

What are Ionic Compounds?

Ionic compounds

- when one or more electrons are transferred from one atom to another, creating a neutral compound- pure substances usually consisting of one metal (donor or giver of electrons – therefore pos. charge) and one non-metal (receiver of electrons – therefore neg. charge)

Some Properties of Ionic Compounds:

- high melting points- ability to form crystals- dissolve in water to form solutions that

conduct electricity- solid at room temperature

Crystal Lattice Solid

Conductivity Soluble in Water

How are Ionic Compounds formed?

Ionic bonds - attraction between oppositely charged ions

How do ions form?

- when one or more electrons move from a metal atom over to a non-metal atom

Rules to follow when writing Formulas and Naming Ionic Compounds:

a) & b) Ion formed from elementsa) Write the symbol for the metal first, then the non-metal.b) Determine the ion charge each element would form.

Write the charge to the upper right of the symbol.

Elements to Combine

a) b)Ion formed

(Element symbol and charge)

MagnesiumChlorine

Mg2+ Cl-

REVIEW – What’s the Charge?

Remember:Look at the valence electrons and ask yourself “What’s

easiest?”.

Let’s review……….

Note the names of the non-metals when they turn into ions.

Predicting Ionic Charges

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

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

Predicting Ionic Charges

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+

Predicting Ionic ChargesGroup 13Group 13:: Loses 3 Loses 3 electrons to form electrons to form 3+3+ ions ions

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

Predicting Ionic ChargesGroup 14Group 14:: Lose 4 Lose 4 electrons or gain electrons or gain 4 electrons?4 electrons?

Neither!Neither! Group 14 Group 14 elements rarely elements rarely form ions.form ions.

Predicting Ionic Charges

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

Predicting Ionic Charges

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

Predicting Ionic Charges

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

Predicting Ionic Charges

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

Predicting Ionic ChargesGroups 3 - Groups 3 - 1212::

Many Many transitiontransition elements elements have more than one possible oxidation have more than one possible oxidation state.state.Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic ChargesGroups 3 - Groups 3 - 1212::

Some Some transitiontransition elements elements have only one possible oxidation state.have only one possible oxidation state.

Zinc = Zn2+ Silver = Ag+

c) Determine the number of each ion needed to balance the charge.

Elements to Combine

a) b)Ion formed

(Element symbol and charge)

c) Balance the

charges

MagnesiumChlorine

Mg2+ Cl- Mg2+ Cl-

Cl-

Total: 2 + and 2 –

Overall charge = 0

Criss-Cross Rule: Place the charge of one ion as the subscript of the other ion.

d) Write the chemical formulaRewrite the symbols together (no spaces) with the number of each needed as subscripts, reduce if possible

Elements to Combine

a) b)Ion formed

(Element symbol and charge)

c) Balance the

charges

d)Write the chemical formula

MagnesiumChlorine Mg2+ Mg2+ Cl-

MgCl2 Cl-

Cl-

e) Write the name of the metal first, then the nonmetal by changing

the ending to “ide”.

Elements to Combine

a) b)Ion formed

(Element symbol and charge)

c) Balance the

charges

d)Write the chemical formula

e)Name the compound

MagnesiumChlorine

Mg2+ Mg2+ Cl- Cl-

Cl- MgCl2 Magnesium Chloride

Polyatomic Ions

A polyatomic ion

• is a group of atoms.

• has an overall ionic charge.Some examples of polyatomic ions are

NH4+ ammonium OH− hydroxide

NO3−

nitrate NO2−

nitrite

CO32−carbonate PO4

3− phosphate

HCO3− hydrogen carbonate(bicarbonate)

Naming Polyatomic Ions

The names of common polyatomic anions

• end in ate.

NO3− nitrate PO4

3− phosphate

• with one oxygen less end in ite.

NO2− nitrite PO3

3− phosphite

Naming Compounds with Polyatomic Ions.

• The positive ion is named first, followed by the name of the polyatomic ion.

NaNO3 sodium nitrate

K2SO4 potassium sulfate

(NH4)3PO3 ammonium phosphite

Writing Formulas with Polyatomic Ions.

• The Criss-Cross Rule still applies

Na+ and NO3− -> NaNO3

• with two or more polyatomic ions has the polyatomic ions in parentheses.

Mg2+ and 2NO3−

-> Mg(NO3)2

subscript 2 for charge balance