Ch 7.1 Forming Ions

Review…

• Cations are Groups 1A, 2A, and 3A– They have positive charges.

• Anions are Groups 5A, 6A, and 7A– They have negative charges– They end in “ide”

• Majority of elements in Groups 4A and 8A do not usually form ions.

• These are called monatomic ions!

Ions of Transition Metals

• Some transition metals in Groups 1B-8B form more than one cation with different charges.

• Examples:– Iron forms Fe2+ and Fe3+

• Two methods of naming: – Stock System: Iron (II) ion and Iron (III) ion– Classical name: Ferrous ion and Ferric ion

*We will use the stock system.

Common Metal Ions with More than One Ionic Charge

Symbol Stock Name Classical Name

Cu+ Copper(I) ion Cuprous ion

Cu2+ Copper(II) ion Cupric ion

Fe2+ Iron(II) ion Ferrous ion

Fe3+ Iron(III) ion Ferric ion

*Hg22+ Mercury(I) ion Mercurous ion

Hg2+ Mercury(II) ion Mercuric ion

Pb2+ Lead(II) ion Plumbous ion

Pb4+ Lead(IV) ion Plumbic ion

Common Metal Ions with More than One Ionic Charge

Symbol Stock Name Classical Name

Sn2+ Tin(II) ion Stannous ion

Sn4+ Tin(IV) ion Stannic ion

Cr2+ Chromium(II) ion Chromous ion

Cr3+ Chromium(III) ion Chromic ion

Mn2+ Manganese(II) ion Manganous ion

Mn3+ Manganese(III) ion Manganic ion

Co2+ Cobalt(II) ion Cobaltous ion

Co3+ Cobalt(III) ion Cobaltic ion

Other Transition Metal Ions

• Some transition metals have only one charge and do not use a Roman numeral.

• Examples (Write on your periodic table!)– Silver: Ag+

– Cadmium: Cd2+

– Zinc: Zn2+

Polyatomic Ions• The names of most polyatomic anions

end in “-ite” or “-ate”

• The “-ite” ending indicates one less oxygen atom than the “-ate” ending

• Remember to use parentheses if more than one is needed.

Write the formula that will form between Ba and ClSolution:1. Write the positive ion of metal first, and then negative ion

Ba2+ Cl 2. Do the charges equal zero? NO!! 3. Use Criss-Cross method – write

subscripts

Ba2+ Cl1 BaCl2

Write the correct formula for the compounds containing the following ions:

1. Na+, S2-

2. Al3+, Cl-

3. Mg2+, N3-

4. Al3+, S2-

1. Na+, S2-

Na2S

2. Al3+, Cl-

AlCl3

3. Mg2+, N3-

Mg3N2

4. Al3+, S2-

Al2S3

Binary Compound: is composed of two elements and can be either

ionic or molecular.

Naming Binary Ionic Compounds

• To name a binary ionic compound, place the cation name first, followed by the anion name.

• Remember the anion ends in “-ide”• Examples:

– Cs2O– NaBr– CuO

Cesium OxideSodium BromideCopper(II) Oxide

Naming Compounds withPolyatomic Ions

• State the cation first and then the anion just as you did in naming binary ionic compounds.– KNO3

– Mg(ClO2)2

Potassium NitrateMagnesium Chlorite

Naming Binary Molecular Compounds

• Binary molecular compound: must be composed of two nonmetals

• Use prefixes to indicate the number and kind of atom in the compound

• Use the following general format:

1st name: prefix + element name2nd name: prefix + element name + “ide”

If there is only 1 of the 1st element, no prefix.

Prefixes in Covalent Compounds pg 228

Number of atoms

Prefix Number of atoms

Prefix

1 mono- 6 hexa-

2 di- 7 hepta-

3 tri- 8 octa-

4 tetra- 9 nona-

5 penta- 10 deca-

Anyone want a cold glass of dihydrogen monoxide?

Examples

• Name the following– CO

– CO2

– N2O

– Cl2O8

Carbon Monoxide

Carbon Dioxide

Dinitrogen Monoxide

Dichlorine Octoxide

Writing Formulas for Binary Molecular Compounds• Use the prefixes in the name to tell you

the subscript of each element in the formula.

• Then write the correct symbols for the two elements with the appropriate subscripts.

• The least electronegative element is written first

• Dinitrogen Tetroxide - N2O4

Examples

• Write formulas for the following:– Nitrogen Monoxide

– Carbon Tetrachloride

– Diphosphorous Pentoxide

NO

CCl4

P2O5

Naming Acids

• An acid is a compound that contains one or more hydrogen atoms and produces hydrogen ions (H+) when dissolved in water.

• All acids begin with hydrogen

• General Format: HnX

– “X” represents a monatomic or polyatomic anion.

– “n” represents the number of hydrogen ions

3 Rules for Naming Common Acids

• If the name of “X” ends in -ate:

____________-ic acid

• If the name of “X” ends in -ite:

____________-ous acid

• If the name of “X” ends in -ide:

hydro-__________-ic acid

Name these acids

• H2SO4

• HCl

• H2S

• HNO3

• HClO2

Sulfuric Acid

Hydrochloric Acid

Hydrosulfuric Acid

Nitric Acid

Chlorous Acid

Writing Formulas for Acids

• If the acid ends in –ic, then “X” ends in –ate

• If the acid ends in –ous, then “X” ends in –ite

• If the acid has hydro-______-ic, then “X” ends in –ide.

• The subscript on hydrogen is equal to the charge of “X”.

Write the Formula for the Following Acids

• Hydrobromic Acid

• Carbonic Acid

• Phosphoric Acid

• Sulfurous Acid

HBr

H2CO3

H3PO4

H2SO3

Homework

• 7.1 pg 251 #14, 15(a-d), 41

Ch 7.3 Using Chemical Formulas

The Mass of a Mole of an Element

• Molar Mass: is the atomic mass of an element expressed in grams/mole (g/mol).

• Carbon = 12.01 g/mol

• Hydrogen = 1.01 g/mol

• When dealing with molar mass, round off to two decimals. 12.011 g/mol 12.01 g/mol

The Mass of a Mole of a Compound• You calculate the mass of a molecule by

adding up the molar masses of the atoms making up the molecules.

• Example: H2O– H = 1.01 g x 2 atoms = 2.02 g/mol– O = 16.00 g x 1 atom = 16.00 g/mol

• Molar Mass of H2O = 2.02 g/mol + 16.00 g/mol = 18.02 g/mol

• This applies to both molecular and ionic compounds

• Find the molar mass of PCl3

– P = 30.97 g x 1 atom = 30.97 g/mol– Cl = 35.45 g x 3 atoms = 106.35 g/mol– PCl3 = 30.97 g + 106.35 g = 137.32 g/mol

• What is the molar mass of Sodium Hydrogen Carbonate (NaHCO3) ?– Na = 22.99 g x 1 atom = 22.99 g/mol– H = 1.01 g x 1 atom = 1.01 g/mol– C = 12.01 g x 1 atom = 12.01 g/mol– O = 16.00 g x 3 atoms = 48.00 g/mol– NaHCO3 = 22.99 + 1.01 + 12.01 + 48.00 = 84.01 g/mol

Converting Moles to Mass

• You can use the molar mass of an element or compound to convert between the mass of a substance and the moles of a substance.

• Mass (g) = # of moles x mass (g)

1 mole

Example: If molar mass of NaCl is 58.44 g/mol, what is the mass of 3.00 mol NaCl?

Mass of NaCl = 3.00 mol x 58.44g =

1 mol

175 g NaCl

Example 2: Moles to Mass

• What is the mass of 9.45 mol of Aluminum Oxide (Al2O3)?

• Find molar mass of Al2O3

= 101.96 g/mol

• Mass = 9.45 mol Al2O3 x 101.96 g Al2O3

1 mol Al2O3

= 964 g Al2O3

Converting Mass to Moles• You can invert the conversion factor to find

moles when given the mass.

• Moles = mass (g) x 1 mole

mass (g)

Example: If molar mass of Na2SO4 142.05 g/mol, how many moles is 10.0 g of Na2SO4?

Moles of Na2SO4 = 10.0 g x 1 mol =

142.05 g= 0.0704 mol Na2SO4

Example 2: Mass to Moles

• How many moles are in 75.0 g of Dinitrogen Trioxide?

• Find molar mass of N2O3

= 76.02 g/mol

• Moles = 75.0 g N2O3 x 1 mole =

76.02 g

N2O3

0.987 mol N2O3

Percent Composition

• Percent Composition: the relative amount of the elements in a compound.

• Also known as the percent by mass

• It can be calculated in two ways:– Using Mass Data– Using the Chemical Formula

% mass of element= mass of element x100% mass of compound

Example• When a 13.60 g sample of a compound containing

Mg and O is decomposed, 5.40 g O is obtained. What is the % composition of this compound?

Mass of compound: 13.60 g

Mass of oxygen: 5.40 g O

Mass of magnesium: 13.60 g - 5.40 g = 8.20 g Mg

% Mg = 8.20 g Mg x 100% =

13.60 g

% O = 5.40 g O x 100% =

13.60 g

60.3%

39.7%

• Find the percent composition of Cu2S.

• Find mass of Cu and S– Cu = 63.55 x 2 = 127.10 g– S = 32.07 g

• Find mass of Cu2S

– 127.10 g + 32.07 g = 159.17 g

% Composition – Cu = 127.10 g x 100% =

159.17 g– S = 32.07 g x 100% =

159.17 g

79.85%

20.15%

• Find the percentage by mass of water in the hydrate Na2CO310H2O

• Find the mass of 10H2O

– H2O = 10 mol x 18.02 g/mol = 180.2 g

• Find the mass of Na2CO310H2O

– Na2CO3 = 1 mol x 105.99 g/mol =105.99 g

– 105.99 g + 180.2 g = 286.2 g

• % By Mass of Water – H2O = 180.2 g H2O x 100% =

286.2 g Na2CO310H2O

62.96%

Homework

• 7.3 pg 253 #30-33

Ch 7.4Determining Chemical Formulas

Empirical Formulas

• Empirical Formula: shows the smallest whole-number ratio of the atoms of the elements in a compound.

• Example: – The Empirical Formula for Hydrogen Peroxide

(H2O2) is HO with a 1:1 ratio.

– The Empirical Formula for Carbon Dioxide (CO2) is CO2 with a 1:2 ratio.

Determining the Empirical Formula of a Compound

• A compound is found to contain 25.9% Nitrogen and 74.1% Oxygen. What is the Empirical Formula of the compound?

• 25.9 g N x 1 mol N = 14.01 g N

• 74.1 g O x 1 mol O = 16.00 g O

• N1.85O4.63 = N1O2.5 = N2O5

1.85 mol N

4.63 mol O

Molecular Formulas• Molecular Formula: tells the actual number

of each kind of atom present in a molecule of a compound

• Example: – The Molecular Formula for Hydrogen Peroxide is

H2O2.

– The Molecular Formula for Carbon Dioxide is CO2

• It is possible to find the Molecular Formula using the Empirical Formula if you know the molar mass of the compound.

Finding the Molecular Formula• Calculate the molecular formula of a

compound whose molar mass is 60.0 g/mol and empirical formula is CH4N

• Step 1: Find the empirical formula molar mass– 12.01 + (4 x 1.01) + 14.01 = 30.06 g/mol

• Step 2: Divide molar mass by EF molar mass– 60.0 g/mol = 1.99 2

30.06 g/mol

• Step 3: Multiply empirical formula by 2– CH4N x 2 = C2H8N2

Homework

• 7.4 pg 253 #36-38