H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Chemical Formula Like a word

• Lists what elements are present in the compound

• Describes Compounds

• Subscripts = how many atoms of element to left of #.

• Expresses the ratio of each element present

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Chemical Formula cont..• Example: CaI2

• The small 2 is a subscript. It indicates that for each molecule of calcium iodide, 1 atom of calcium is present for each 2 atoms of iodine.

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Chemical Formula Chemical Formula PracticePracticeConsider the formula for Consider the formula for

potassium nitrate (KNOpotassium nitrate (KNO33):):

How many atoms of How many atoms of nitrogen are present?nitrogen are present?

How many atoms of oxygen are How many atoms of oxygen are present?present? 3

How many atoms of How many atoms of potassium are present?potassium are present?

1

1

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Your Turn…..

CaCl2KClMgBr2

Na2S

Sr3N2

How many atoms of each element are in each of the formulas below?

Pb2(CrO4)3

NH4NO2

Mg(NO3)2

(NH4)2S

Ca(NO3)2

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Remember…….Ionic Compounds

• Composed of (+) cation and (-) anion for a net charge of zero

• These charges are also called “oxidation numbers”

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Charges?

Cations:• Group 1 A = +1

• Group 2A = +2

• Group 3A (metals (below the zig-zag line)) = +3

• Group 4A (metals (below the zig-zag line)) = +4

• Group 5A (metals (below the zig-zag line))= +5

• Group 6A (metal (below the zig-zag line)) = +6

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Charges? Cont…

Anions:• Group 8A = 0 (noble gases)

• Group 7A = -1

• Group 6A = -2

• Group 5A (non metals (above the zig-zag line)) = -3

• Group 4A (non metals (below the zig-zag line)) = -4

• Group 3A (non metals (below the zig-zag line)) = -5

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

IONIC Bonds in IONIC compounds!

• What does ION mean? Charged particles

• Remember our example…NaCl.

+-

ZERO

• How do atoms become charged?

gain or give away ELECTRONS

+-+-+-+-+-

• The whole compound has to equal

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

How do I write Ionic Compound Formulas ?

1. Write each element’s symbol with its charge = ion formula

2. Place the Cation (+) ion first and then place the anion (-) second.

3. Move the superscript (charge of the first ion) to the bottom (subscript) of the second ion.

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

How do I write Ionic Compound Formulas ?

4. Make the subscripts positive (+).Note: If the subscript is 1 then no

subscript is needed.

Double check: The charges X the # of ions on each ion should add up to a net charge of zero.

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Lets Practice…

Cation Anion Formula Na+ O-2 = Na2O

Write the formula for Sodium Oxide

Na2O = 2 atoms of Na+ & 1 atom of O-2 Na+ + Na+ + O-2

= 0(+1) + (+1) + (-2) = 0

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

This is called the “criss-cross” method

Cation Anion Formula Ca+2 Cl-1 = CaCl2

Al+3 Cl-1 = AlCl3

Li+1 N-3 = Li3N

Mg+2 N-3 = Mg3N2

Calcium chloride

Aluminum

chloride

Lithium nitride

Magnesium nitride

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Your Turn…..Write the Formula for aluminum

sulfideCation Anion Formula Al+3 S-2 =

Al+3 + Al+3 + S-2 + S-2 + S-2 = 0

Al2S3

+3 + +3 + -2 + -2 + -2

= 0

Al2S3 = 2 atoms of Al+3 & 3 atom of S-2

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

What about transitional elements?1. If given the name, the charge is

provided with a Roman numeral

2. If given the formula, write the charge in Roman numerals in parenthesis

iron (II) oxide = Fe+2 and O-2 = FeO

copper (I) oxide = Cu+1 and O-2 = Cu2O

Pb2O4 = Pb+4 and O-2 = lead (IV) oxide

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Transitional elements are easy…cobalt (III) chloride

gold (I) sulfide

lead (II) iodide

iron (III) oxide

chromium (II) sulfide

copper (II) chloride

lead (IV) iodide

CoCl3

Au2S

PbI2

Fe2O3

CrS

CuCl2

PbI4

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Name these transitional elementsmanganese (IV) oxide

chromium (III) oxide

lead (II) chloride

iron (III) iodide

chromium (III) sulfide

copper (I) chloride

platinum (IV) iodide

Mn2O4

Cr2O3

PbCl2

FeI3

Cr2S3

CuCl

PtI4

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Polyatomic Ions• Group of bonded atoms w/a chargePlace polyatomic ion in ( ) and treat as

one unit and place the subscript on the outside of the ().

• If the polyatomic is taken only once then () are not needed.

• Ex: (PO4)3-

Phosphate ion with 3- charge

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Common Polyatomic ions

+ 1 charge

- 1 -2 -3

NH4+

Ammonium

OH-

Hydroxide

CO3-2

Carbonate

PO4-3

Phosphate

NO3-

Nitrate

SO4-2

Sulfate

NO2-

Nitrite

SO3-2

Sulfite

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Lets Practice… Formula for potassium carbonate

Cation Anion Formula K+ (CO3)-2 =

remove parentheses K2CO3

K+ K+ (CO3)-2

=0

K2(CO3)

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Formula for zinc nitrateCation Anion

Formula Zn+2 (NO3)-1 =

Zn(NO3)2

Zn+2 (NO3)-1 (NO3)-1 = 0

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

What about Ionic Formulas with Polyatomics?

NH4 & Cl

Al & NO3

Ca & CO3

K & PO4

(NH4)2Clammonium chloride

Al(NO3)3aluminum nitrate

CaCO3calcium carbonate

K2PO4potassium phosphate

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

Let’s put it all together…

sodium hydroxidemercury (II) sulfatelead (IV) phosphateammonium sulfidealuminum chloratecopper (I) carbonatemanganese (IV) oxidealuminum nitrateiron (II) phosphatesodium chromateammonium chromate

NaOHHgSO4

Pb3(PO4)4

(NH4)2SAl(ClO3)3

Cu2CO3

Mn2O4

Al2(NO3)3

FePO4

Na2CrO4

(NH4)2CrO4

H2C

H2C

H2C

H2C

H2C

H2C

H2C

CH2

CH2

CH2

CH2

CH2

CH2

How about the other way?calcium hydroxidelead (II) sulfatecopper (II) phosphateammonium oxidealuminum bromatecopper (II) carbonatemanganese (IV) sulfidealuminum sulfateiron (III) phosphatelithium chromateammonium carbonate

Ca(OH)2

PbSO4

Cu3(PO4)2

(NH4)2OAl(BrO3)3

CuCO3

Mn2S4

Al2(SO4)3

Fe2(PO4)3

Li2CrO4

(NH4)2CO3