chemical names & formulas chapter 9. section overview 9.1: naming ions 9.2: naming and writing...

CHEMICAL NAMES & FORMULASChapter 9

Section Overview• 9.1: Naming Ions• 9.2: Naming and Writing Formulas for Ionic Compounds• 9.3: Naming and Writing Formulas for Molecular

Compounds• 9.4: Naming and Writing Formulas for Acids and Bases• 9.5: The Law Governing Formulas and Names

NAMING IONSSection 9.1

Monatomic Ions• Remember, ionic compounds consist of a positive metal

ion and a negative nonmetal ion combined in a proportion such that their charges add up to a net charge of zero.

• Some ions, which make up ionic compounds, are monatomic ions and consist of a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons.

Monatomic Ions• Cations: Have a positive charge and therefore lose

electrons.• When the metals in Groups 1A, 2A, and 3A lose electrons,

they form cations with positive charges equal to their group number.

• All group 1A ions have a 1+ charge.• All group 2A ions have a 2+ charge.• All group 3A ions have a 3+ charge.• The names of cations are the same as the name of the

metal, followed by the word ion (ex. sodium ion Na+).

Monatomic Ions• Anions: Have a negative charge and therefore lose

electrons.• The charge of any ion of a Group A nonmetal is

determined by subtracting 8 from the group number.• All Group 7A ions have a 1- charge (7-8 = -1).• All Group 6A ions have a 2- charge (6-8 = -2).• All Group 5A ions have a 3- charge (5-8 = -3).• Anions names start with the m of the element name and

end in –ide (ex. fluorine F vs fluoride ion F-)

Monatomic Ions• Ions of Transition Metals: Form more than one cation with

different ionic charges.• The charges of the cations of many transition metal ions

must be determined from the number of electrons lost.• Two methods are used to name these ions, but the

preferred is the Stock system.• A roman numeral in parentheses is placed after the name

of element to indicate the numerical value of the charge (ex. Iron (III) ion for Fe3+).

Monatomic Ions• Example Problem: Write the symbol for the ion formed by

each element. Classify the ions as cations or anions. Name the ion.

a. Potassiumb. Iodinec. Sulfurd. Lead, 4 electrons lost

Monatomic Ions• Example Problem: Write the symbol for the ion formed by

each element. Classify the ions as cations or anions. Name the ion.

a. Potassiumb. Iodine• Solution:Find the charge using the group number of the element, cation or anion, name.a. Potassium = K+, cation, potassium ionb. Iodine = I-, anion, iodide ion

Monatomic Ions• Example Problem: Write the symbol for the ion formed by

each element. Classify the ions as cations or anions. Name the ion.

c. Sulfurd. Lead, 4 electrons lost• Solution:c. Sulfur = S2-, anion, sulfide iond. Lead, 4 electrons lost = Pb4+, cation, lead (IV) ion

Polyatomic Ions• Some ions, called polyatomic ions, are composed of more

than one atom.• The names of most polyatomic ions end in –ite or –ate.• Sometimes the same two or three elements combine in

different ratios to form different polyatomic ions (ex. SO32-

and SO42-, sulfite and sulfate).

NAMING AND WRITING FORMULAS FOR IONIC COMPOUNDSSection 9.2

Binary Ionic Compounds• Naming Binary Ionic Compounds: A binary compound is

composed of two elements and can be either ionic or molecular.

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

• Examples:Cs2O = cesium oxideNaBr = sodium bromideSrF2 = strontium fluoride CuO = copper (II) oxide

Binary Ionic Compounds• Writing Formulas for Binary Ionic Compounds: If you know

the name of a binary ionic compound, you can write its formula.

• Write the symbol of the cation and then the anion then add whatever subscripts are needed to balance the charges (ex. Potassium chloride is KCl, K+ and Cl- ratio = 1:1).

• Another method, is called the crisscross method.• The numerical value of the charge of each ion is crossed

over and becomes the new subscript for the other ion.

Binary Ionic Compounds• Crisscross Method

Compounds with Polyatomic Ions• Write the symbol for the cation followed by the formula for

the polyatomic ion and balance the charges.• You can still use the crisscross method here (shown on

previous slide) just make sure to keep polyatomic ions in parentheses and the subscript on the outside.

• To name a compound containing a polyatomic ion, state the cation first and then anion just as in binary compounds (ex. LiCN is lithium cyanide, NAClO is sodium hypochlorite).

NAMING AND WRITING FORMULAS FOR MOLECULAR COMPOUNDSSection 9.3

Naming Binary Molecular Compounds

• In a molecular compounds, both elements are nonmetals and they are not ions.

• Since binary compounds are made of molecules and not ions, charges cannot be used to write formulas or to name them.

• The prefix in the name of a binary molecular compounds tells how many atoms of each element are present in each molecule of the compound.

• 1 = mono, 2 = di, 3 = tri, 4 = tetra, 5 = penta, 6 = hexa, 7 = hepta, 8 = octa, 9 = nona, and 10 = deca.

• Example: CO is carbon monoxide and CO2 is carbon dioxide.

Naming Binary Molecular Compounds

• Guidelines:1. Confirm that the compound is a molecular compounds

and not ionic – between two nonmetals.2. Name the elements in the order listed in the formula.3. Use prefixes to indicate the number of each kind of

atom (omit mono- when the formula contains only one atom of the first element in the name).

4. The suffix of the second element is –ide.Examples: SF6 = sulfur hexafluoride N20 = dinitrogen oxide Cl2O8 = dichlorine oxtoxide

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.

Examples: silicon carbide = SiC dinitrogen pentoxide = N2O5

NAMING AND WRITING FORMULAS FOR ACIDS AND BASESSection 9.4

Naming Acids• An acid is compound that contains one or more hydrogen

atoms and produces hydrogen ions (H+) when dissolved in water.

• When naming an acid, you can consider the acid to consist of anion combined with as many hydrogen ions are needed to make the molecule electrically neutral.

• Therefore, the chemical formulas for acids are in the general form HnX where X is a monatomic or polyatomic anion and n is a subscript indication the number of hydrogen ions that are combined with the anion.

Naming Acids• Three rules can be used to name an acid with the general

formula HnX.1. When the name of the anion (X) ends in –ide, the acid

name begins with the prefix hydro-. The stem of the anion has the suffix –ic and is followed by the word acid (Ex. HCl (X = chloride) is named hydrochloric acid and H2S (X = sulfide) is named hydrosulfuric acid).

2. When the anion name ends in –ite, the acid name is the stem of the anion with the suffix –ous, followed by the word acid (Ex. H2SO3 (X=sulfite) is named sulfurous acid).

3. When the anion name ends in –ate, the acid name is the stem of the anion with the suffix –ic followed by the word acid (Ex. HNO3 (X=nitrate) is named nitric acid).

Writing Formulas for Acids• If you know the name of an acid, you can write its formula.• Use the rules for writing the names of acids in reverse to

write the formulas for acids.Examples: Hydrobromic acid = HBr (use rule #1)

Phosphorous acid = H3PO3 (rule #2) Formic acid = HCOOH (rule #3)

Names and Formulas for Bases• A base is an ionic compounds that produces hydroxide

(OH-) ions when dissolved in water.• Bases are named the same way as other ionic

compounds – the name of the cation is followed by the name of the anion (Ex. NaOH = sodium hydroxide).

• To write the formulas for bases, write the symbol for the metal cation followed by the formula for the hydroxide ion and balance the charges (Ex. Aluminum (Al+3) hydroxide (OH-) = Al(OH)3).

THE LAWS GOVERNING FORMULAS AND NAMESSection 9.5

The Laws of Definite and Multiple Proportions

• The rules for naming and writing formulas for compounds are possible only because compounds form from the elements in predictable ways.

• These ways are summed up in two laws: the law of definite proportions and the law of multiple proportions.

• Law of Definite Proportions: In samples of any chemical compounds the masses of the elements are always in the same proportions.

• Law of Multiple Proportions: Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.

Calculating Mass Ratios• Example Problem: Carbon reacts with oxygen to form two

compounds. Compound A contains 2.41g of carbon dioxide for each 3.22g of oxygen. Compound B contains 6.71g of carbon for each 17.9 grams of oxygen. What is the lowest whole number mass ratio of carbon that combines with a given mass of oxygen?

Calculating Mass Ratios• Example Problem:. Compound A contains 2.41g of carbon

dioxide for each 3.22g of oxygen. Compound B contains 6.71g of carbon for each 17.9 grams of oxygen. What is the lowest whole number mass ratio of carbon that combines with a given mass of oxygen?

• Solution:Knowns UnknownCompound A = 2.41g C and 3.22g O Lowest ratioCompound B = 6.71g C and 17.9g O

2.41gC/3.22gO = 0.748gC/1.00gC6.71gC/17.9gO = 0.375gC/1.00gC0.748gC/0.375C = 1.99/1 = 2/1 = 2:1