Learning Chemical Formulas

Simple Ionic Compounds Concept: Ionic Formulas are formed from positive and negative ions. Fact 1: Positive ions are formed by metals that lost electrons. Examples: Na 1+ Mg 2+ A 3+

Simple Ionic Compounds zFact 2: Negative ions are formed by nonmetals that gained electrons. Examples: Cl 1- O 2- N 3-

Simple Ionic Compounds Fact 3: The overall charge of ionic compounds must equal zero. Examples : Na 1+ Cl 1- Ca 2+ Br 1- Al 3+ O 2-

How does that work? Ions: Na 1+ Cl 1- Ca 2+ Br 1- Al 3+ O 2- For ionic compounds, the subscripts tell you the ratio of ions. Positive charge has to cancel out negative charge. Compounds: NaCl CaBr 2 Al 2 O 3

Lesson Two--Polyatomic Ion Formulas Concept: Polyatomic ions are groups of atoms that behave as one unit. Fact 4: Some ions have more that one atom but their overall charge can be determined. Examples: (SO 4 ) = S +6 and O -8 = -2 (NO 3 )= N +5 and O -6 = -1 (NH 4 ) = N -3 and H +4 = +1

Polyatomic Ion Formulas Fact 5: These group ions, polyatomic ions, are treated like single ions in formulas, but must have parentheses when more than one is used in a formula. Examples: Ca 2+ (NO 3 ) 1- 2 Ga 3+ (SO 4 ) 2- (NH 4 ) 1+ 2 O 2-

Polyatomic Ion Formulas Fact 6: The polyatomic ions are named based on the atoms that they contain. Those with oxygen and another nonmetal are often name "____ate" with the root of the other nonmetal in the blank. Examples: (NO 3 ) 1- is nitrate (SO 4 ) 2- is sulfate (ClO 3 ) 1- is chlorate

Polyatomic Ion Formulas Fact 7: Those polyatomic ions with one oxygen less than the "ate" ions are named "----ite" ions. Examples: (NO 2 ) 1- is nitrite (SO 3 ) 2- is sulfite (ClO 2 ) 1- is chlorite

Lesson Three--Transition Metal Compounds Concept: Transition metals have electrons in d orbitals and can donate different numbers of electrons, thus giving them several different positive charges. Fact 10: These can be determined from the Roman numeral which is written next to the metal's name. Example: Cu 1+ is Copper I Pb 2+ is Lead II Fe 3+ is Iron III Sn 4+ s Tin IV

Transition (B block) Metals zThese metals can ionize differently, depending on conditions. zRoman Numerals (I, II, III, IV) tell you the charge of the metal. zExamples: Iron (II) oxide, Lead (IV) oxide Fe 2+ O 2- Pb 4+ O 2- zBecomes FeO becomes PbO 2

Transition Metal Compounds Fact 11: These transition metals are used in formulas just like other metals, once the charge is determined from the Roman numeral in the name. Example: Cu 1+ Cl 1- Pb 2+ O 2- Fe 3+ Br 1- 3 Sn 4+ O 2-

Transition Metal Compounds Fact 12: A few transition metal ions only have one charge and never change so they can be written without a Roman numeral in their formula name. Example: Ag 1+ Zn 2+ Cd 2+

A Note about naming from formulas: zIf it’s molecular/covalent, yUse prefixes yName ends in –ide zIf it’s ionic, yNo prefixes yName ends in –ide unless there is a polyatomic ion. Then it ends in –ite or –ate.

Today’s Assignment (due Thurs). zPortfolio pages 10 (if not done already), 11, 14, 15

Lesson Four--Using Formulas in Problem Solving Concept: Correctly written chemical formulas hold a large amount of information for the prepared student to find. Fact 13: The subscripts tell us the number of atoms of each kind that is present in the compound. Example: NaCl has one atom of sodium and one atom of chlorine. H 2 SO 4 has two atoms of hydrogen, one atom of sulfur and four atoms of oxygen

Using Formulas in Problem Solving Fact 14: The sum of the atomic masses times the number of atoms of each kind of element is equal to the mass of one mole of the substance. Examples: Na = 23g/mol and Cl = 35.5g/mol so NaCl has a molar mass of 58.5g/mol Nitric acid is HNO 3 so its molar mass is H = 1 x 1 = 1 N = 14 x 1 = 14 O = 16 x 3 = 48 Total = 63g/mol

Using Formulas in Problem Solving Fact 15: From the formula ion charges, also called oxidation numbers, can be determined using simple math processes. Example:Fe 2 O 3 is iron oxide, but what is the charge of the iron in this formula? It is known that the oxygen's ionic charge is -2 so substitute in that charge and find the iron's ionic charge. Fe -- 2 O -2 3 It is clear that the missing charge is +3. Thus the complete name of this compound is iron III oxide.

Using Formulas in Problem Solving Fact 16: The percentage composition of each element in a compound can be determined using only the correct formula and the atomic masses. Example: Sodium chloride or NaCl Na = 23.0 % Na = 23.0 x 100 = 39.3%Na Cl = g/mol % Cl = 35.5 x 100 = 60.7% Cl 58.5 Notice that the total of the percentages is always equal or very close to 100%.