Chemical Formula & Naming Chapter 7

CCl4 MgCl2 Guess the name of each of the above compounds based on the formulas written. What kind of information can you discern from the formulas? Guess which of the compounds represented is molecular(covalent) and which is ionic. Chemical formulas form the basis of the language of chemistry and reveal much information about the substances they represent.

example: octane — C8H18 Carbons = 8 Hydrogens = 18 A chemical formula indicates the relative number of atoms of each kind in a chemical compound. example: octane — C8H18 Carbons = 8 Hydrogens = 18

example: aluminum sulfate — Al2(SO4)3 Parentheses surround the polyatomic ion to identify it as a unit. The subscript 3 refers to the unit. Note also that there is no subscript for sulfur: when there is no subscript next to an atom, the subscript is understood to be 1.

Monatomic Ions Many main-group elements can lose or gain electrons to form ions. Ions formed from a single atom are known as monatomic ions. example: To gain a noble-gas electron configuration, nitrogen gains three electrons to form N3– ions. Some main-group elements tend to form covalent bonds instead of forming ions. examples: carbon and silicon

Naming Monatomic Ions Monatomic cations are identified by the element’s name. examples: K+ is called the potassium cation Mg2+ is called the magnesium cation For monatomic anions, the ending of the element’s name is dropped, and the ending -ide is added to the root name. F– is called the fluoride anion N3– is called the nitride anion

Binary compounds Compounds composed of two elements are binary compounds. In a binary ionic compound: positive charges = negative charges The formula for a binary ionic compound can be written cation 1st , anion 2nd . example: magnesium bromide Ions combined: Mg2+, Br–, Br– Chemical formula: MgBr2

Example Aluminum Chloride Al +3 Cl -1 AlCl3

Example Sodium Sulfide Na +1 S -2 Na2S

Example Magnesium Oxide Mg +2 O -2 MgO

Sample Problem Write the formulas for the binary ionic compounds formed between the following elements: a. iodine and zinc b. zinc and sulfur

Polyatomic Ions Many common polyatomic ions are oxyanions—polyatomic ions that contain oxygen. Examples: PO4, SO4, NO2

Polyatomic Ions (cont.) Some elements can combine with oxygen to form more than one type of oxyanion. example: nitrogen NO3- NO2- The name of the ion with the greater number of oxygen atoms ends in -ate. The smaller number of oxygen atoms ends in -ite. nitrate nitrite

Mg SO4 MgSO4 Example Magnesium Sulfate +2 -2 -ate and -ite endings are polyatomics Magnesium Sulfate Mg +2 SO4 -2 MgSO4

Example Aluminum Nitrite Al +3 NO2 -1 Al(NO2)3

Example Calcium Hydroxide Ca +2 OH -1 Ca(OH)2

Example Iron (III) Oxide Fe +3 O -2 Fe2O3

Sample Problem Write the formula for tin(IV) sulfate.

Example Ba3N2 barium nitride

Example Na3PO4 sodium phosphate

CuO Example Copper (II) Oxide Copper ( ) Oxide Copper (I) – Cu+1 Which copper is it? -2 X 1 atom = -2 Copper (II) Oxide Copper ( ) Oxide Copper (I) – Cu+1 Copper (II) – Cu+2

FeCl3 Example Iron (III) Chloride Iron (II) – Fe+2 Iron (III) – Fe+3 Which iron is it? -1 X 3 atom = -3 Iron (III) Chloride Iron (II) – Fe+2 Iron (III) – Fe+3

Cu3PO4 Example Copper (I ) Phosphate Copper ( ) Phosphate Which copper is it? -3 X 1 atom = -3 +3/3 Cu atoms = +1 Copper (I ) Phosphate Copper ( ) Phosphate Copper (I) – Cu+1 Copper (II) – Cu+2

Naming Binary Molecular Compounds Molecular compounds are composed of individual covalently bonded units. Naming molecular compounds is based on the use of prefixes. examples: CCl4 — carbon tetrachloride CO — carbon monoxide CO2 — carbon dioxide

Prefixes 1 – mono 2 – di 3 – tri 4 – tetra 5 – penta 6 – hexa 7 – hepta 8 – octa 9 – nona 10 - deca

Naming (cont.) Rule – Use prefixes to tell how many of each atom; 1st atom name from periodic table, 2nd element gets –ide ending Exception – If only 1 of first atom, NO mono-

Prefixes

Example Dichlorine heptabromide Cl2 Br7

S O3 Example Sulfur trioxide Note: no “mono” when only one of first element

Sample Problem a. Give the name for As2O5. b. Write the formula for oxygen difluoride.

Example F3P4 trifluorine tetraphosphide

Example CO2 carbon dioxide

Example CO carbon monoxide

Warm-UP Potassium carbonate Dinitrogen pentachloride CBr4 AuP Mercury(I) selenide

Acids Can be either: Binary acids are acids that consist of two elements, usually hydrogen and a halogen. Oxyacids are acids that contain hydrogen, oxygen, and a third element (usually a nonmetal).

Naming Acids – Create the rules Examples of binary acids: Hydrochloric acid HCl Hydrofluoric acid HF Examples of oxyacids: phosphoric acid H3PO4 nitric acid HNO3 sulfuric acid H2SO4

Acid Chart ____-ide ____-ate ____-ite hydro-___-ic acid _____-ic acid Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

HBr Example bromide = hydrobromic acid ____-ide ____-ate ____-ite Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

H3N Example nitride = hydronitric acid ____-ide ____-ate ____-ite Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

HNO3 Example nitrate = nitric acid ____-ide ____-ate ____-ite Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

Hydrosulfuric acid Example H+1 S-2 = H2S ____-ide ____-ate ____-ite Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

H2SO3 Example sulfite = sulfurous acid ____-ide ____-ate ____-ite Ion ending ____-ide ____-ate ____-ite Acid name is… hydro-___-ic acid _____-ic acid _____-ous acid

All Mixed Up Determine compound type Ionic – starts with metal or NH4 Covalent – starts with nonmetal Acid – starts with hydrogen Use proper rules to write formula/name

Section 7-3 The chemical formula for water is H2O. How many atoms of hydrogen and oxygen are there in one water molecule? How might you calculate the mass of a water molecule, given the atomic masses of hydrogen and oxygen?

Chemical formulas allow chemists to calculate a number of characteristic values for a compound: formula mass molar mass percentage composition

The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all atoms represented in its formula. example: formula mass of water, H2O average atomic mass of H: 1.01 amu average atomic mass of O: 16.00 amu average mass of H2O molecule: 18.02 amu

formula mass of KClO3 = 122.55 amu Sample Problem: Find the formula mass of potassium chlorate, KClO3 formula mass of KClO3 = 122.55 amu

A compound’s molar mass is numerically equal to its formula mass. Ex.) the molar mass of pure calcium, Ca, is 40.08 g/mol because one mole of calcium atoms has a mass of 40.08 g. Ex.) molar mass of H2O molecule: 18.02 g/mol

molar mass of Ba(NO3)2 = 261.35 g/mol Sample Problem G What is the molar mass of barium nitrate, Ba(NO3)2? molar mass of Ba(NO3)2 = 261.35 g/mol

Molar Mass as a conversion factor

Sample Problem What is the mass in grams of 2.50 mol of oxygen gas (O2)? moles O2  grams O2 amount of O2 (mol)  molar mass of O2 (g/mol) = mass of O2 (g)

Sample Problem Ibuprofen, C13H18O2, is the active ingredient in many nonprescription pain relievers. Its molar mass is 206.31 g/mol. If the tablets in a bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle? How many molecules of ibuprofen are in the bottle? What is the total mass in grams of carbon in 33 g of ibuprofen?

Percent Composition To find the mass percentage of an element in a compound, the following equation can be used. Mass of element/mass of total sample x 100 = percent comp.

Sample Problem Find the percentage composition of copper(I) sulfide, Cu2S.

More problems From data: What is the percent composition of a compound made from 222.6 g Na and 77.4 g O? From formula: Find the percent composition of sodium sulfate.

Empirical Formula The simplest ratio of atoms in a compound Need percent composition to find it

Empirical formula, cont. Example: Find the empirical formula of a compound that is 79.9% C and 20.1 % H. Assume 100 g Convert to moles Divide by smallest number of moles *If all are close to whole numbers, stop *If NOT, multiply all to make them all whole 4. Write the formula

Empirical formula, cont. Ex: Find the empirical formula of a compound that is 17.6% Na, 39.7% Cr, and 42.7% O. Assume 100 g Convert to moles Divide by smallest number of moles *If all are close to whole numbers, stop *If NOT, multiply all to make them all whole 4. Write the formula

Example: diborane The percentage composition is 78.1% B and 21.9% H. What is the empirical formula?

Sample Problem: Quantitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. Find the empirical formula of this compound.

Molecular Formulas NOT the simplest ratio Is a MULTIPLE of the empirical formula Ex. C2H4  CH2 Molecular formula Empirical formula

Molecular formulas, cont. Ex. A compound that is 58.8% C, 9.8% H, and 31.4% O, has a molecular/formula mass of 204 g/mol. Find its formula mass. Find the empirical formula Find mass of the empirical formula Divide molecular mass by empirical mass to find multiplier Write the molecular formula

Chapter Review Pg. 251 #’s 2-8, 10-12, 14, 23, 30-32, 35-38

Mole review 1 mole = 6.02E23 atoms 1 mole = ____g 1 mole = 6.02E23 molecules 1 mole = 6.02E23 formula units How many formula units are in 4.3 grams silver nitrate? How many moles is 3.43 X 1024 molecules carbon dioxide? How many grams is 2.65 X 1023 atoms of aluminum?