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Chapter 5 – Molecules and Compounds

Chapter 5 – Molecules and Compounds. Law of Constant Composition Every sample of a compound has the same proportions of constituent elements.

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Chapter 5 – Molecules and Compounds

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  1. Chapter 5 – Molecules and Compounds Law of Constant Composition • Every sample of a compound has the same proportions of constituent elements. • If we were to decompose ammonia, NH3, we would 14 g of nitrogen for every 3 g of hydrogen. Ammonia has a constant Mass Ratio of nitrogen to hydrogen of 4.7:

  2. Chapter 5 – Molecules and CompoundsWhy Do Compounds Show Constant Composition? • The smallest piece of a compound is called a molecule. • Every molecule of a compound has the same number and type of atoms. • Since all the molecules of a compound are identical, every sample will have the same ratio of the elements. • Since all molecules of a compound are identical, every sample of the compound will have the same properties.

  3. Chapter 5 – Molecules and Compounds Chemical Formulas • describe compounds by describing the number and type of each atom in the simplest unit of the compound • molecules or ions • each element is represented by its letter symbol • the number of atoms of each element is written to the right of the element as a subscript • if there is only one atom, the 1 subscript is not written • never change for a given compound • polyatomic groups are placed in parentheses • if more than one

  4. Chapter 5 – Molecules and Compounds • The formula for water is H2O. So, there are two atoms of hydrogen and 1 atom of oxygen in water. • The formula for sugar is C12H22O11. So, there are 12 atoms of carbon, 22 atoms of hydrogen and 11 atoms oxygen in sugar. • Example #1: Determine the number of each type of atom in each of the following formulas. a) CdS b) Al2O3 c) Al(OH)3 d)Ba(BrO3)2 • 1 cadmium atom, 1 sulfur atom • 2 aluminum atoms, 3 oxygen atoms • 1 aluminum, 3 oxygens, 3 hydrogens • 1 barium, 2 bromines, 6 oxygens

  5. Chapter 5 – Molecules and Compounds Order of Elements in a Formula • the more positively charged element is written first • metals are written first • NaCl • nonmetals are written in order from Table 5.1, • CO2 • there are occasional exceptions for historical or informational reasons • H2O, but NaOH

  6. Example #2: Write chemical formulas for • compounds containing: • one barium atom and two chlorine atoms • b) two iron atoms and three oxygen atoms • three hydrogen atoms, one phosphorus atom, • and four oxygen atoms • d) one lead atom, two oxygen atoms, and two hydrogen atoms BaCl2 Fe2O3 H3PO4 Pb(OH)2

  7. Chapter 5 – Molecules and Compounds A Molecular View of Elements and Compounds • Atomic elements are elements whose particles are single atoms. • Molecular elements are elements whose particles are multi-atom molecules. • Molecular compounds are compounds whose particles are molecules made of only nonmetals • Ionic compounds are compounds whose particles are cations and anions.

  8. Chapter 5 – Molecules and Compounds • Molecular Elements • usually exist as diatomic molecules in which two atoms of that element are bonded together • there are 7 common diatomic elements • find the element with atomic number 7, N, make a figure 7 by going over to Group 7A, then down to iodine • include H2

  9. Chapter 5 – Molecules and Compounds • Molecular compounds • two or more non-metals • smallest unit is a molecule • examples include: H2O, CO2, acetone or C3H6O • Ionic Compounds • formed from metals and nonmetals • metal cations attracted to nonmetal anions • do not have individual molecule units, instead have 3-dimensional arrays or lattices of cations and anions made of formula units • examples include: NaCl, CaCO3, Mg(OH)2

  10. Chapter 5 – Molecules and Compounds Example #3: Classify each of the following substances as an atomic element, molecular element, molecular compound, or ionic compound and give the basic units that compose them. a) O2 b) CsHCO3 c) C12H22O11 d) Na • Molecular element, diatomic molecules • Ionic compound, formula units • Molecular compound, molecules • Atomic element, single atoms

  11. Chapter 5 – Molecules and Compounds Writing Formulas for Ionic Compounds • Write the chemical symbols and charges for the metal and nonmetal. • Remember that the charges of many elements can be determined from the group number on the periodic chart. • Make the magnitude of the charge on each ion be the subscript for the other ion. • Reduce the subscripts to give the smallest whole numbers. • Check that the sum of the positive charge cancels out the sum of the negative charge.

  12. Chapter 5 – Molecules and Compounds Example #4: Write a formula for the ionic compound that forms from each of the following pairs of elements. • potassium and bromine • aluminum and fluorine • Magnesium and phosphorus • Sodium and selenium - KBr - AlF3 - Mg3P2 - Na2Se

  13. Chapter 5 – Molecules and Compounds Naming Ionic Compounds • Name by simply naming the ions • If cation is: • Type I metal = metal name • Type II metal = metal name(charge) • Polyatomic ion = name of polyatomic ion • If anion is: • Nonmetal = stem of nonmetal name + ide • Polyatomic ion = name of polyatomic ion

  14. Chapter 5 – Molecules and Compounds • Type I • metals whose ions can only have one possible charge • IA, IIA, (Al, Ga, In) • determine charge by position on the Periodic Table • IA = +1, IIA = +2, (Al, Ga, In = +3) • Type II • metals whose ions can have more than one possible • charge • determine charge by charge on anion • usually transition metals, exceptions include tin and lead

  15. Chapter 5 – Molecules and Compounds Example #5: Determine if the following metals are Type I or Type II. If the metal Type I, determine the charge on the cation it forms. • lithium • copper • gallium • tin • strontium - Type I, +1 - Type II - Type I, +3 - Type II - Type I, +2

  16. Chapter 5 – Molecules and Compounds Example #6: Classify each of the following ionic compounds as a Type I or Type II ionic compound. • Ca(OH)2 • HgO • Fe2O3 • AlCl3 • CuSO4 - Type I - Type II - Type II - Type I - Type II

  17. Chapter 5 – Molecules and Compounds Naming Type I Binary (Two Elements) Compounds • The cation is always named first and the anion second. • A cation takes its name from the name of the metal. • An anion is named by taking the first part of the element name and adding –ide. Example #7: Give the name for the compound CaI2. Solution: 1) The cation is calcium. 2) The anion is iodine. 3) Iodine becomes iodide. 4) The correct name is calcium iodide.

  18. Chapter 5 – Molecules and Compounds Naming Type II Binary (Two Elements) Ionic Compounds 1. The cation is always named first and the anion second. 2. The cation takes its name from the name of the metal and is followed by a Roman Numeral in parentheses to indicate its charge. - Determine the charge of the cation by multiplying the magnitude of the charge of the anion by the number of anions and dividing your result by the number of cations. - Common Type II cations are in Table 5.5 in your text book. 3. An anion is named by taking the first part of the element name and adding –ide.

  19. Chapter 5 – Molecules and Compounds Example #8: Give the name for the compound Hg2O. Solution: • The cation is mercury • The anion is oxygen. • The charge of the cation is equal to magnitude of anion charge X number of anions / number of cations and 2 X 1 / 2 = 1 So, the charge on mercury is +1. 4) Oxygen becomes oxide. 5) The correct name is mercury (I) oxide.

  20. Chapter 5 – Molecules and Compounds Naming Ionic Compounds Containing a Polyatomic Ion • Polyatomic ions are single ions that contain more than one atom. • Most polyatomic ions are oxyanions or anions that contain oxygen. Oxyanions in a series are named systematically according to the number of oxygen atoms in the ion. • If there are only two ions in an oxyanion series, then the ion with more oxygen atoms is given the ending –ate and the one with less oxygen atoms is given the ending –ite. • If the oxyanion series has more than two ions, then the prefixes hypo- (less than) and per- (more than) are used. ClO- hypochlorite ClO2- chlorite ClO3- chlorate ClO4- perchlorate • The cation is always named first and the anion second.

  21. Chapter 5 – Molecules and Compounds Example #9:Name each of the following compounds a) Al2(SO4)3 b) (NH4)NO2 c) Cr(C2H3O2)2 d) NaClO4 e) Co3(PO4)2 • aluminum sulfate • ammonium nitrite • chromium (II) acetate • sodium perchlorate • cobalt (II) phophate

  22. Chapter 5 – Molecules and Compounds • Naming Binary (Two Elements) Molecular Compounds • 1. Name first element in formula first • - Use the full name of the element • 2. Name the second element in the formula • with an -ide as if it were an anion, however, • remember these compounds do not contain • ions! • 3. Use a prefix in front of each name to indicate • the number of atoms • - Never use the prefix mono- on the • first element

  23. Chapter 5 – Molecules and Compounds • Use prefixes to indicate the number of • atoms present. Drop the “a” if the name • of the element begins with a vowel. • 1 = mono- (not used on first nonmetal) • 2 = di- • 3 = tri- • 4 = tetra- • 5 = penta- • 6 = hexa- • 7 = hepta- • 8 = octa-

  24. Chapter 5 – Molecules and Compounds Example #10: Name each of the following molecular compounds. a) SeO b) SiO2 c) GeH4 d) P2S5 e) NH3 f) P4O6 • selenium monoxide • silicon dioxide • germanium tetrahydride • diphosphorous pentasulfide • nitrogen trihydride (ammonia) • tetraphosphorus hexoxide

  25. Chapter 5 – Molecules and Compounds Naming Acids • Acids produce H+ ions when dissolved in water. • If an acid does not contain oxygen, the acid is named using the following formula: hydro prefix + stem of the name of the element or anion + ic suffix • If the acid does contain oxygen, it is an oxyacid and the name of the acid is formed from the root name of the first element in the polyatomic anion or the anion name, with a suffix of –ic or -ous. • If the polyatomic ion ends in –ate then the suffix –icis used. • If the polyatomic ion ends in –ite then the suffix –ousis used.

  26. Chapter 5 – Molecules and Compounds Example #11: Name the following binary acids. • HBr • HF • H2S • HCN • hydrobromic acid • hydrofluoric acid • hydrosulfuric acid • hydrocyanic acid or hydrogen bromide or hydrogen fluoride or dihydrogen sulfide or hydrogen cyanide

  27. Chapter 5 – Molecules and Compounds Example #12: Name the following oxyacids. • HNO2 • H2SO4 • H3PO4 • HClO • HMNO4 • nitrous acid • sulfuric acid • phosphoric acid • hypochlorous acid • permanganic acid

  28. Chapter 5 – Molecules and Compounds Formula Mass • Average mass of the molecules or formula units that compose a compound. • Calculated using the following equation: Formula mass = (# of atoms of 1st element in formula X Atomic mass of 1st element) + (# of atoms of 2nd element in formula X Atomic mass of 2nd element) + …

  29. Chapter 5 – Molecules and Compounds Example #16: What is the correct formula and formula mass of calcium carbonate? Formula mass = (1 X Atomic mass of Ca) + (1 X Atomic mass of C) + (3 X Atomic mass of O) Formula mass = (1 X 40.08 amu) + (1 X 12.01 amu) + (3 X 16.00 amu) = 100.09 amu CaCO3

  30. Chapter 5 – Molecules and Compounds Example #17: What is the correct formula and formula mass of lead (II) acetate? Formula mass = (1 X Atomic mass of Pb) + (4 X Atomic mass of C) + (6 X Atomic mass of H) + (4 X Atomic mass of O) Formula mass = (1 X 207.2 amu) + (4 X 12.01 amu) + (6 X 1.01 amu) + (4 X 16.00 amu) = 325.3 amu Pb(C2H3O2)2

  31. Chapter 5 Homework Due the day of Exam 2 1, 3, 5, 8, 24, 26, 32, 36, 42, 48, 50, 54, 56, 60, 64, 66, 72, 76, 80, 82, 90, 94

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