Chapter 7 Chemical Formulas and Chemical Compounds Chemical

Chapter 7 Chemical Formulas and Chemical Compounds

Chemical Formulas • Number of atoms of each kind • Examples – C 8 H 18 – Al 2(SO 4)3

Monatomic Ions • Formed by gaining or losing electrons • S-block – +1 or +2 charge • P-Block – Groups 15, 16, 17 • 1 -, 2 -, or 3 - charge – Group 14 • 2+ charge

Monatomic Ions • D-block – 2+, 3+ charge • Sometimes 1+ and 4+ • Nomenclature – Cations • Element’s name – Anion • Ending of name is dropped • Add -ide

Binary Ionic Compounds • • • Composed of 2 atoms Neutral compounds Cation written first Cross over to balance charge Name of cation given first Name of anion given second

Problem • Write the formulas for the binary ionic compounds formed between the following elements – Zinc and iodine – Zinc and sulfur – Potassium and iodine – Magnesium and chlorine – Sodium and sulfur – Aluminum and nitrogen

Problem • Name the binary ionic compounds indicated by the following formulas – Ag. Cl – Zn. O – Ca. Br 2 – Sr. F 2 – Ba. O – Ca. Cl 2

Binary Ionic Compounds • Elements that form 2 or more cations • Stock System – Use Roman numerals to indicate ion’s charge • Examples – Fe 2+ →Iron(II) – Fe 3+ →Iron(III) • Cu. Cl 2 →copper(II) chloride

Problem • Write the formula and give the name for the compound formed by the ions – Cr 3+ and F– Cu 2+ and Br– Fe 2+ and O 2– Pb 2+ and Cl– Sn 2+ and F– Hg 2+ and S 2 -

Problem • Give the names for the following compounds – Cu. O – Co. F 3 – Sn. I 4 – Fe. S

Polyatomic Ions • Oxyanions – One less oxygen →-ite – One less oxygen than -ite →hypo– One more oxygen than -ate →per- • • Cl. O- →hypochlorite Cl. O 2 - →chlorite Cl. O 3 - →chlorate Cl. O 4 - →perchlorate

Problem • Write the formula for – tin(IV) sulfate – Lithium nitrate – Copper(II) sulfate – Sodium carbonate – Calcium nitrite – Potassium perchlorate

Problem • Give the names for the following compounds – Ca(OH)2 – KCl. O 3 – NH 4 OH – Fe. Cr. O 4 – KCl. O

Binary Molecular Compounds • 2 nomenclature systems – Stock system – Prefixes • CCl 4 →carbon tetrachloride • CO →carbon monoxide • CO 2 →carbon dioxide

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

Rules 1. Less electronegative element 1 st 2. 2 nd element →combine prefix, root, and ending -ide 3. O or a of prefix is dropped when root starts with vowel • P 4 O 10 →tetraphosphorus decoxide

Problem • Name the following binary molecular compounds – As 2 O 5 – SO 3 – ICl 3 – PBr 5

Problem • Write the formula for – Oxygen difluoride – Carbon tetraiodide – Phosphorus trichloride – Dinitrogen trioxide

Oxidation Numbers 1. Atoms in pure element → 0 2. More electronegative element → negative charge as an anion 3. Fluorine →-1 4. Oxygen →-2 1. Exceptions: peroxides →-1 fluoride →+2 5. Hydrogen →+1 1. Exception: w/metals →-1

Oxidation Numbers 6. Sum of neutral compound equals 0 7. Sum of atoms in polyatomic ion equals charge of ion

Problems • Assign oxidation numbers to each atom in the following compounds or ions: – HF – H 2 O – UF 6 – H 2 SO 4 – Cl. O 3 -

Problems • Assign oxidation numbers to each atom in the following compounds or ions: – CF 4 – SO 2 – P 4 O 10 – HCl. O 3

Oxidation Numbers, Formulas, & Names • Oxidation numbers can be used like ionic charges to determine formulas • Use stock system – Roman numerals show oxidation number • SO 2 - sulfur(IV) oxide • SO 3 - sulfur(VI) oxide

Problem • Give the name according to the stock system of the following compounds: – PCl 3 – N 2 O – Pb. O 2 – CI 4 – As 2 S 3 – NCl 3

Problem • Give the formula for the following compounds: – Sodium(I) oxide – Sulfur(II) chloride – Nitrogen(V) oxide – Carbon(IV) sulfide – Phosphorus(III) iodide

Formula & Molar Masses • Molecules and ions have average mass • H 2 O → 18. 02 amu • Numerically equal to molar mass – Mass of one mole of a compound – H 2 O → 18. 02 g/mol

Problems • What is the molar mass of: – KCl. O 3 – H 2 SO 4 – Ca(NO 3)2 – Ba(OH)2 – Na. NO 3 – Al 2 S 3

Conversions • Molar mass is a conversion factor – g/mol – mol/g

Problems • What is the mass in grams of 2. 50 mol of oxygen gas? • What is the mass in grams of 0. 257 mol of calcium nitrate? • How many moles are in 3. 82 g SO 2? How many molecules are in this sample of SO 2?

Problem • Ibuprofen, C 13 H 18 O 2, is the active ingredient in many nonprescription pain relievers. Its molar mass is 206. 29 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?

Percentage Composition • Percentage by mass of an element in compound • (mass of element)/(mass of compound) x 100 = % element in compound

Problem • Find the percentage composition of copper(I) sulfide, Cu 2 S. • Calculate the percentage composition of sodium nitrate.

Problem • As some salts crystallize from a water solution, they bind water molecules in their crystal structure. Sodium carbonate forms such a hydrate, in which 10 water molecules are present for every formula unit of sodium carbonate. Find the mass percentage of water in sodium carbonate decahydrate, Na 2 CO 3· 10 H 2 O, which has a molar mass of 286. 14 g/mol.

Empirical Formulas • Compound with subscripts showing smallest whole-number mole ratio of atoms – BH 3 vs. B 2 H 6 • • Convert percent composition to mass composition Convert mass composition to composition in moles

Empirical Formulas • • Divide each number of moles by smallest number of moles Round to nearest whole number

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.

Problem • Analysis of a 10. 150 g sample of a compound known to contain only phosphorus and oxygen indicates a phosphorus content of 4. 433 g. What is the empirical formula of this compound?

Molecular Formula • x(empirical formula) = molecular formula • Must know formula mass • (Experimental formula mass)/(Empirical formula mass)

Problem • The empirical formula of a compound of phosphorus and oxygen was found to be P 2 O 5. Experimentation shows that the molar mass of this compound is 283. 89 g/mol. What is the compound’s molecular formula?

Problem • Determine the molecular formula of the compound with a empirical formula of CH and a formula mass of 78. 110 amu • A sample of a compound with a formula mass of 34. 00 amu is found to consist of 0. 44 g H and 6. 92 g O. Find its molecular formula.

Chapter Review • Pg. 251 – 3 abcd, 4 bcd, 5 de, 6 ace, 7 bd, 8 ab, 10 ace, 11 cd, 16 cd, 23 bce, 24 bce, 25 bde, 28 ac, 30 bd, 31, 32, 36, 38