AP Chemistry. Slide 1 / 163. Slide 2 / 163. Slide 3 / 163. Compounds. Table of Contents: Compounds Pt. A

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1 Slide 1 / 163 Slide 2 / 163 AP Chemistry Compounds Table of Contents: Compounds Pt. A Slide 3 / 163 Click on the topic to go to that section Chemical Formulas Metals & Alloys Ionic Compounds Covalent Compounds

2 Slide 4 / 163 Chemical Formulas Return to Table of Contents The Mole Slide 5 / 163 Recall that 1 mole is defined as x units of a given substance. 1 mol of electrons = x electrons 1 mol of 2 molecules = x molecules of water 1 mol of NaCl formula units = x formula units NaCl 1 mol of K atoms = x atoms of K The Mole Slide 6 / 163 Within 1 mole of a compound, there are often differing moles of each element In 1 mole of aluminum nitrate, Al(N 3) 3 = 1 mol of Al 3+ ions = 3 mol of N - 3 ions = 3 mol of N atoms = 9 mol of atoms

3 1 ow many moles of oxygen atoms are present in 2.0 moles of aluminum nitrate Al(N 3) 3? Slide 7 / ow many moles of oxygen atoms are present in 2.0 moles of aluminum nitrate Al(N 3) 3? Slide 7 () / moles 2 ow many moles of oxygen atoms are in 2.0 moles of sodium sulfate, Na 2S 4? Slide 8 / 163

4 2 ow many moles of oxygen atoms are in 2.0 moles of sodium sulfate, Na 2S 4? Slide 8 () / moles 3 ow many hydroxide ions are present in 1.2 x formula units of magnesium hydroxide: Mg() 2? Slide 9 / ow many hydroxide ions are present in 1.2 x formula units of magnesium hydroxide: Mg() 2? Slide 9 () / x hydroxide ions

5 Molar Mass and Volume Slide 10 / 163 Recall that the mass of 1 mol of a substance is called the molar mass and is measured in g/mol. This can be found on the periodic table. Molar mass of CaCl 2 = 110 g/mol Molar Mass of Ag = 108 g/mol Recall also that 1 mol of any gaseous substance will occupy 22.4 L of space at STP. 1 mol of Ar(g) = mol of 2(g) = What is the volume by 88 grams of carbon dioxide? Slide 11 / What is the volume by 88 grams of carbon dioxide? Slide 11 () / L

6 5 ow many ml of methane gas (C 4) are in a 100 gram sample of a gas that is 32% methane by mass? Slide 12 / 163 Natural gas (methane) pipeline. 5 ow many ml of methane gas (C 4) are in a 100 gram sample of a gas that is 32% methane by mass? Slide 12 () / ,800 ml Natural gas (methane) pipeline. 6 Which of the following contains the most atoms of? Slide 13 / 163 A 2 grams of 2 gas B 16 grams of methane (C 4) C 22.4 L of 2 gas D 9 grams of water ( 2)

7 6 Which of the following contains the most atoms of? Slide 13 () / 163 A 2 grams of 2 gas B 16 grams of methane (C 4) C 22.4 L of 2 gas B D 9 grams of water ( 2) 7 ow many moles of fluoride ions (F-) are present in a 79 gram sample of SnF 2? Slide 14 / 163 A 0.5 moles B 78.5 moles C 1 mole D 1.5 moles 7 ow many moles of fluoride ions (F-) are present in a 79 gram sample of SnF 2? Slide 14 () / 163 A 0.5 moles B 78.5 moles C 1 mole D 1.5 moles C

8 Chemical Formulas Slide 15 / 163 A chemical formula provides the ratio of atoms or moles of each element in a compound. 2 = 2 atoms or 2 mol 1 atom 1 mol Al(N 3) 3 = 1 Al 3+ ion or 1 mol Al 3+ ions 3 N 3 - ions 3 mol N 3 - ions Empirical and Molecular Formulas Slide 16 / 163 An empirical formula provides the simplest whole number ratio of atoms or moles of each element in a compound. Examples: 2, NaCl, C 3 5 A molecular formula represents the actual number of atoms or moles of each element in a compound. Examples: 2, C 3 5, C Calculating an Empirical Formula Slide 17 / 163 To find an empirical formula: 1. Determine the moles of each element within the compound then... Compound "X" consists of 1.2 g C, 0.2 g, and 1.6 g = 0.1 mol C, 0.2 mol, and 0.1 mol 2. Find the whole number ratio of these moles by dividing by smallest mole value! 0.1 mol C = 1 C 0.2 mol = mol = mol 0.1 mol 0.1 mol Empirical formula = C 2

9 Calculating a Molecular Formula Slide 18 / 163 Determining the molecular formula of a compound is easy once the empirical formula and the molecular weight of the compound are known. 1. Determine the ratio of the molecular weight to the empirical formula weight. MW of Compound "X" = 60 u Empirical formula weight of C 2 = 30 u Ratio = 60/30 = 2/1. The molecule is twice as heavy as the empirical formula. 2. Multiply each subscript of empirical formula by the ratio determined in step 1 C 2 x 2 = C = Molecular Formula 8 Practice Students type their answers here Given the following data, calculate the empirical formula of phosphine gas. Phosphine gas is created by reacting solid phosphorus with 2(g). Mass of P(s) initial 1.45 g 1.03 g Mass of 2(g) initial Mass of P(s) unreacted Mass of 2(g) unreacted g g Slide 19 / Practice Students type their answers here Given the following data, calculate the empirical formula of phosphine gas. Phosphine gas is created by reacting solid phosphorus with 2(g) g P reacted = mol P reacted Mass of P(s) initial Mass of P(s) unreacted g 2 reacted = mol g mol 2 = mol g / = / = 1 P Mass of 2(g) initial Mass of 2(g) unreacted P3 = empirical formula g g Slide 19 () / 163

10 9 Practice Students type their answers here Black iron oxide (aka magnetite) is used as a contrast agent in MRI scans of human soft tissue. To determine the empirical formula, a student reacted solid iron with 2(g). Fe(s) reacted Mass of iron oxide obtained g 4.22 g Slide 20 / 163 What is the empirical formula? 9 Practice Students type their answers here Black iron oxide (aka magnetite) is used as a contrast agent in MRI scans of human soft tissue. To determine the empirical formula, a student reacted 3.05 solid g Fe = iron with mol Fe 2(g) = 1.17 g 2(g) Fe(s) reacted Mass of iron oxide obtained g 2(g) = mol g mol 2 = mol g 0.055/0.055 = 1 Fe 0.073/0.055 = 1.33 mol What x each is the by 3 empirical to get a whole formula? number ratio... Slide 20 () / 163 Fe34 Practice Students type their answers here Butane gas can be produced when solid carbon is reacted with hydrogen gas. If 0.45 grams of carbon were found to react with 1.05 L of 2 what is the molecular formula of butane given it has a molar mass of 58 g/mol. 10 Slide 21 / 163

11 Practice Students type their answers here Butane gas can be produced when solid carbon is reacted with hydrogen gas. If 0.45 grams of carbon were found to react with L of 2 what is the molecular formula of butane 0.45 g C = mol C given it has a molar mass of 58 g/mol L 2(g) = mol 2(g) mol 2(g) = mol / = 1 C x 2 = C / = 2.5 x 2 = 5 Slide 21 () / 163 Empirical Formula = C25 58/29 = 2 Molecular Formula = C Which of the following is NT an empirical formula? Slide 22 / 163 A Fe 2 3 B 2NN 2 C C 3 D C 3C 2Cl 11 Which of the following is NT an empirical formula? Slide 22 () / 163 A Fe 2 3 B 2NN 2 C C 3 D C 3C 2Cl B

12 12 A compound used in airbags degrades into sodium and nitrogen gas (N 2) when ignited. If 3.36 L of N 2(g) was from an initial mass of the compound of 6.50 grams, what is the empirical formula? Slide 23 / 163 A Na 2N 3 B Na 3N C NaN 3 D NaN 12 A compound used in airbags degrades into sodium and nitrogen gas (N 2) when ignited. If 3.36 L of N 2(g) was from an initial mass of the compound of 6.50 grams, what is the empirical formula? Slide 23 () / 163 A Na 2N 3 B Na 3N C NaN 3 D NaN C 13 A compound containing carbon, hydrogen, and chlorine is 14.1% carbon by mass, 83.5% Cl, with the rest being hydrogen. What is the empirical formula? Slide 24 / 163 A C 2 5Cl B C 2Cl 2 C C 2 6Cl D C 3Cl

13 13 A compound containing carbon, hydrogen, and chlorine is 14.1% carbon by mass, 83.5% Cl, with the rest being hydrogen. What is the empirical formula? Slide 24 () / 163 A C 2 5Cl B C 2Cl 2 C C 2 6Cl D C 3Cl B 14 ydrazine is a component of rocket fuel. It consists of 87.5% N with the rest being hydrogen by mass. If the molecular weight of the compound is 32 grams/mol, what is the molecular formula? Slide 25 / 163 A N 2 B N 3 C N 2 6 D N ydrazine is a component of rocket fuel. It consists of 87.5% N with the rest being hydrogen by mass. If the molecular weight of the compound is 32 grams/mol, what is the molecular formula? Slide 25 () / 163 A N 2 B N 3 D C N 2 6 D N 2 4

14 Slide 26 / 163 Law of Definite Composition If a compound is pure, it will always consist of the same composition no matter where the sample was taken or the size of the sample. Example: calcium carbonate If it's calcium carbonate, it's guaranteed to be 40% calcium, 48% oxygen, and 12% carbon by mass. Slide 27 / 163 Law of Definite Composition Example: calcium carbonate Sample Location Size Analysis Composition 1 Eastern Pennsylvania 50.0 g 2 Wyoming g 20.0 g Ca 24.0 g 6.0 g C g Ca g 30.0 g C 40% calcium 48% oxygen 12% carbon 40 % calcium 48% oxygen 12% carbon Law of Definite Composition Slide 28 / 163 Some substances are not pure and do not obey the law of definite composition. These are called mixtures. Sea water Sample Size Sample location % mass composition g Atlantic cean 85.3% 10.7 % 1.6% Na 2.4 % Cl g Indian cean 79.5 % 10.0 % 4.2 % Na 6.3 % Cl

15 15 Students type their answers here Practice The law of definite composition can be used mathematically to see how much of a given substance is present in a sample. Slide 29 / 163 Water is known to be 88.9% oxygen and 11.1 % hydrogen by mass. ow many grams of oxygen would be present in a 400 gram sample of pure water? 15 Students type their answers here Practice The law of definite composition can be used mathematically to see how much of a given substance is present in a sample. Slide 29 () / 163 Water is known to be 88.9% oxygen and 11.1 % hydrogen by mass. ow many grams of oxygen would be present in a 400 gram sample of pure water? 400 g of 2 x g = 355 g 1 g 2 16 Students type their answers here Practice If a sample of water was found to contain 34.1 grams of oxygen, how many grams of hydrogen and water would be present? Slide 30 / 163

16 16 Students type their answers here Practice If a sample of water was found to contain 34.1 grams of oxygen, how many grams of hydrogen and water would be present? Slide 30 () / g x g = 4.26 g g 34.1 g x 1 g 2 = 38.4 g g 17 ydrogen peroxide is known to be 94.1 % oxygen by mass with the rest being hydrogen. ow many grams of hydrogen would be present in a pure 230. gram sample of hydrogen peroxide? Slide 31 / ydrogen peroxide is known to be 94.1 % oxygen by mass with the rest being hydrogen. ow many grams of hydrogen would be present in a pure 230. gram sample of hydrogen peroxide? Slide 31 () / g [This object is a pull tab]

17 18 Calcium oxide is 71.4% calcium by mass with the rest being oxygen. ow many grams of calcium would be present if a sample of calcium oxide sample was found to contain 12.3 grams of oxygen? Slide 32 / Calcium oxide is 71.4% calcium by mass with the rest being oxygen. ow many grams of calcium would be present if a sample of calcium oxide sample was found to contain 12.3 grams of oxygen? Slide 32 () / g [This object is a pull tab] 19 Calcium carbonate is known to be 40% Ca, 48%, and 12% carbon by mass. When a 200 gram sample of what is thought to be pure calcium carbonate is decomposed, 18 grams of carbon are found in the sample. Is this substance pure? Slide 33 / 163 Yes No

18 19 Calcium carbonate is known to be 40% Ca, 48%, and 12% carbon by mass. When a 200 gram sample of what is thought to be pure calcium carbonate is decomposed, 18 grams of carbon are found in the sample. Is this substance pure? Slide 33 () / 163 Yes No N [This object is a pull tab] Law of Definite Composition and the Classification of Matter This law allows us to classify the different types of matter MATTER Does the material obey the Law of Definite composition? Slide 34 / 163 Yes Pure Substance No Mixture Can the material be broken down into different elements with distinct properties? Yes Compounds No Elements 20 Two samples of a material are taken and the composition of each sample is given below. Is this material a pure substance? Slide 35 / 163 Yes Sample A Sample B No 45 % Cu, 12% Si, 43 % 34% Cu, 19% Si, 47 %

19 21 A certain material is found to vary in composition by mass. What kind of matter is this? Slide 36 / 163 A Element B Compound C Mixture D Pure Substance 21 A certain material is found to vary in composition by mass. What kind of matter is this? Slide 36 () / 163 A Element B Compound C Mixture C D Pure Substance [This object is a pull tab] 22 Which of the following is TRUE regarding a pure compound? Slide 37 / 163 A It will not obey the law of definite composition B It can be broken down into different elements C The amounts of each element by mass in the compound will not vary D It must contain the same equal mass % of each element in the compound

20 22 Which of the following is TRUE regarding a pure compound? Slide 37 () / 163 A It will not obey the law of definite composition B It can be broken down into different elements C The amounts of each element by mass in the C compound will not vary D It must contain the same equal mass % of each element in the compound [This object is a pull tab] Slide 38 / 163 Metals & Alloys Return to Table of Contents Introduction to Chemical Bonds Slide 39 / 163 A chemical bond is an attraction between atoms to form a compound that contain two or more atoms. The bond forms due to the electrostatic attraction between opposite charges. There are three basic types of bonds: metallic, ionic, and covalent.

21 Sea of Electrons Slide 40 / 163 Recall that metallic atoms lose electrons easily. In a metallic compound, valence electrons become delocalized. Instead of orbiting their specific nuclei, the electrons flow freely in a "sea of electrons" between the positively charged nuclei. Properties of Metals Slide 41 / 163 The free flow of electrons and strong electrostatic force between metallic atoms give metals some unique properties: They are good conductors of heat and electricity They have typically have high melting points They are shiny, malleable and ductile They are readily alloyed (able to form mixtures with other elements) click here for a tutorial on properties of metals Conduction Slide 42 / 163 Metals are good conductors of both heat and electricity because the electrons are delocalized and relatively free to move.

22 Melting Point Slide 43 / 163 Metals have a wide range of melting points but due to high Coulombic attraction between the sea of electrons and the metallic nuclei, these melting points are typically high. Metal Melting Point ( o C) Aluminum 660 Copper 1084 Lead Magnesium 650 Phosphorus 44 Potassium 63.3 Platium 1770 Silver 961 By comparison: Compound/Type MP ( o C) C4/molecule /molecule 0 diamond/covalent network solid NaCl/ionic compound RbBr/ionic compound Structural Properties Slide 44 / 163 Metals are malleable (able to be flatten into sheets) and ductile (able to be pulled into wires) because deforming the solid does not change the environment surrounding the metallic nuclei. The low electronegativity of these atoms allow the electrons to move in response to the change. Metals are shiny because the free flowing electrons are excited by interaction with photons, causing the electrons to vibrate and reflect the light. 23 Electrons are stationary in a metallic compound. Slide 45 / 163 True False

23 23 Electrons are stationary in a metallic compound. Slide 45 () / 163 True False False [This object is a pull tab] 24 Copper is often used to make wires. This is because... (you may select more than one response) Slide 46 / 163 A it is ductile B it has a high electronegativity C it is conductive D its is malleable 24 Copper is often used to make wires. This is because... (you may select more than one response) Slide 46 () / 163 A it is ductile B it has a high electronegativity C it is conductive D its is malleable A and C [This object is a pull tab]

24 25 Most metals are at room temperature. Slide 47 / 163 A gas B liquid C molten D solid 25 Most metals are at room temperature. Slide 47 () / 163 A gas B liquid C molten D solid D [This object is a pull tab] Alloys An alloy is a mixture of two or more metals, or a metal and another element. Slide 48 / 163 There exists three main variants of alloys: eterogeneous alloys Intermetallic alloys omogeneous/ Metal solution alloys

25 eterogeneous Alloys eterogeneous alloys lack a regular crystal structure throughout the solid. Solder (50% Pb and 50% Sn), used in fusing together different metal work pieces, is an example of a heterogeneous alloy. Slide 49 / 163 Intermetallic Alloys Slide 50 / 163 Intermetallic alloys: ave definite proportions of constituent elements ave a crystal structure that is different from any of the constituent metals Result in solids with properties often different from constituent metals Examples: MgZn 2 Na 5Zn 21 Cu 3Zn omogeneous Alloys Slide 51 / 163 omogeneous alloys are alloys with the same crystal lattice structure as one of the constituent elements. There are two types of homogeneous alloys: substitutional alloys and interstitial alloys.

26 Substitutional Alloys Slide 52 / 163 Examples: Brass - copper and zinc Bronze - copper and tin Substitutional alloys consist of atoms of similar sizes. The atoms of the base metal are replaced by atoms of the added element in the matrix. Interstitial Alloys Slide 53 / 163 Interstitial alloys occur when the added element is much smaller than the base metal. The smaller atoms occupy spaces between the base metal atoms in the crystal matrix. Example: Steel - iron and carbon Alloys containing more than 2 elements can be a combination of these types of alloys. Example: Stainless steel - iron, carbon, nickel and chromium 26 Sterling silver is composed of silver and copper. What type of alloy is this? Slide 54 / 163 A interstitial alloy B substitutional alloy C substitutional-institial alloy D it's not an alloy, its an ionic compound

27 26 Sterling silver is composed of silver and copper. What type of alloy is this? Slide 54 () / 163 A interstitial alloy B substitutional alloy C substitutional-institial alloy B D it's not an alloy, its an ionic compound [This object is a pull tab] 27 An alloy is formed using a transition metal and carbon. It retains the crystalline structure of the transition metal. What type of alloy is created? Slide 55 / 163 A etergeneous B omogeneous substitional C omogenous interstitial D Intermetallic 28 A homogenous alloy is formed by 3 elements. Which of the following categories of alloy might in fall into? Slide 56 / 163 A interstitial B substitutional C interstitial/substitutional D any of the above

28 Alloys Metals must be molten in order to be alloyed. Although this requires a large energy input, the resulting alloy has enhanced properties compared to its base metal(s). Slide 57 / 163 Alloys are created to increase strength and reduce malleability (ex. steel and brass) or resist corrosion (ex. stainless steel and sterling silver). Note that the electrical and thermal conductivity of alloys is usually lower than that of its base metal. 29 In general, alloys enhance the properties of metals. Which of the following is a true statement? Slide 58 / 163 A Alloys have increased malleability B Alloys have increased strength C Alloys have increase conductivity D Alloys have increased ductility 29 In general, alloys enhance the properties of metals. Which of the following is a true statement? Slide 58 () / 163 A Alloys have increased malleability B Alloys have increased strength C Alloys have increase conductivity B D Alloys have increased ductility [This object is a pull tab]

29 30 Which of the following would have the highest melting point? Slide 59 / 163 A steel B carbon C iron D they have the same melting point 30 Which of the following would have the highest melting point? Slide 59 () / 163 A steel B carbon C iron A D they have the same melting point [This object is a pull tab] Slide 60 / 163 Ionic Compounds Return to Table of Contents

30 Ionic Compounds Ionic compounds form crystal lattice structures of repeating patterns called unit cells. Unit cells are form in an arrangement that maximizes attractive forces between ions and minimizes repulsion. Slide 61 / 163 Some examples: simple cubic unit cell body-centered cubic unit cell face-centered orthorhombic unit cell click here to review ionic formulas and naming Properties of Ionic Compounds Slide 62 / 163 The strong electrostatic attraction between charges and their crystalline structure gives ionic compounds some unique properties: Conductive only when molten or dissolved in water (aqueous) igh melting points Brittle click here for a tutorial on properties of ionic compounds 31 Most ionic compounds are at room temperature. A gas Slide 63 / 163 B liquid C molten D solid

31 31 Most ionic compounds are at room temperature. A gas Slide 63 () / 163 B liquid C molten D solid D [This object is a pull tab] 32 The brittleness of ionic compounds can be attributed to... Slide 64 / 163 A the electrostatic attraction between the ions B the strength of the ionic bonds C the repeating pattern of its structure D its ability to conduct electricity 32 The brittleness of ionic compounds can be attributed to... Slide 64 () / 163 A the electrostatic attraction between the ions B the strength of the ionic bonds C the repeating pattern of its structure C D its ability to conduct electricity [This object is a pull tab]

32 33 The high melting point of ionic compounds can be attributed to... Slide 65 / 163 A the electrostatic attraction between the ions B their lack of malleability C the repeating pattern of its structure D its ability to conduct electricity 33 The high melting point of ionic compounds can be attributed to... Slide 65 () / 163 A the electrostatic attraction between the ions B their lack of malleability C the repeating pattern of its structure D its ability to conduct electricity A [This object is a pull tab] Slide 66 / 163

33 Ionic Bonding Slide 67 / 163 nce a positive and negative ion are formed, they will be attracted to each other via the electrostatic force. Neutral atom 1 valence electron Low Electronegativity + Cation F = k q1 q2 Neutral atom 7 valence electrons igh Electronegativity - Anion r 2 Ionic Bond Formation Slide 68 / 163 Ionic bonding occurs in a series of steps, most of which require energy but occur because they are coupled to the highly exothermic formation of the bond. Formation of LiF(s) from it's elements in their standard state. Li(s) + 1/2F 2(g) --> LiF(s) Event Reaction Energy Change Sublimation of Li(s) Li(s) --> Li(g) +180 kj/mol Ionization of Li(g) Li(g) --> Li+(g) + e kj/mol Breaking of existing F-F bond 1/2F2(g) --> F(g) +157 kj/mol Ionization of F(g) F(g) + e- --> F-(g) -328 kj/mol Bond formation Li+(g) + F-(g) --> LiF(s) kj/mol verall energy change = -505 kj/mol Notice that breaking bonds is endothermic (requires energy input) while making bonds is exothermic (releases energy) Ionic Bond Formation Slide 69 / 163 The thermochemical steps for ionic bond formation are often summarized in a Born-aber Cycle Diagram The energy released when the gaseous ions combine is known as the Lattice Energy f represents the overall energy change of the process.

34 Lattice Energy Slide 70 / 163 The magnitude of the lattice energy is influenced by the charge and size of the ions involved. The higher the charges, the greater the Coulombic attraction and the higher the lattice energy. Substance Charges Lattice Energy NaF(s) +1 and kj/mol Mg(s) +2 and kj/mol The smaller the ionic radii, the greater the coulombic attraction and the higher the lattice energy Substance Ionic radii Lattice Energy NaF(s) F- = 117 pm -923 kj/mol NaCl(s) Cl- = 167 pm -786 kj/mol 34 Which of the following would have the highest lattice energy? Slide 71 / 163 A Be B MgS C MgCl 2 D MgI 2 34 Which of the following would have the highest lattice energy? Slide 71 () / 163 A Be B MgS C MgCl 2 D MgI 2 A

35 35 Which of the following BEST explains why the lattice energy of CaS is lower than that of Mg? Slide 72 / 163 A Ca has lower ionic charges than Mg B The calcium ion has more shielding than the magnesium ion C The calcium ion has a smaller nuclear charge than magnesium ion D Ca has higher ionic charges than Mg 35 Which of the following BEST explains why the lattice energy of CaS is lower than that of Mg? Slide 72 () / 163 A Ca has lower ionic charges than Mg B The calcium ion has more shielding than the magnesium ion B C The calcium ion has a smaller nuclear charge than magnesium ion D Ca has higher ionic charges than Mg 36 Which of the following BEST explains why the lattice energy of MgF 2 is lower than that of Mg? Slide 73 / 163 A The oxide ion is smaller than the flouride ion B The charge of the cation is higher in Mg C The charge density of the anion is less in MgF 2 D The charge density of the anion is less in Mg

36 36 Which of the following BEST explains why the lattice energy of MgF 2 is lower than that of Mg? Slide 73 () / 163 A The oxide ion is smaller than the flouride ion B The charge of the cation is higher in Mg C C The charge density of the anion is less in MgF 2 D The charge density of the anion is less in Mg 37 Rank the following from lowest to highest melting point. Slide 74 / 163 A I < II < III B I < III < II C II < I < III D III < II < I I. NaBr II. LiBr III. LiF 37 Rank the following from lowest to highest melting point. Slide 74 () / 163 A I < II < III B I < III < II C II < I < III D III < II < I I. NaBr II. LiBr III. LiF D

37 Slide 75 / 163 Covalent Compounds Return to Table of Contents Types of Covalent Compounds Slide 76 / 163 There are two types of compounds created by the covalent bonding of atoms: Molecules - smaller compounds of a one or more elements bonded together, such as water ( 2) or oxygen gas ( 2) Covalent networks - larger compounds consisting of repeating elemental or molecular units all covalently bonded together, such as diamond (C n) or quartz [(Si 2) n] Properties of Covalent Network Compounds Like ionic and metallic substances, covalent network solids are giant molecules with many strong electrostatic attractions. This gives them some unique properties: Non-conductive - because they are made of non-metallic atoms, covalent network solids conduct little or no electricity Slide 77 / 163 ardness - because all atoms in the structure are bonded together, these materials tend to be very hard igh melting points - covalent bonds are strong and covalent networks have many bonds giving them high melting points

38 Diamond vs. Graphite Diamond and graphite are examples of covalent network solids composed of a single element, carbon. They are allotropes - different molecules made of the same element. Slide 78 / 163 Carbon atoms have 4 valence electrons. In diamonds, 4 covalent bonds are formed creating a very strong 3-dimensional shape. In graphite only 3 covalent bonds are formed, creating 2-dimensional sheets of carbon atoms. The fourth electron wanders freely over the surface of the sheet, allowing graphite to be somewhat conductive. Graphite is soft because the 2-D sheets are held together by weak intermolecular forces; very little force is required to break these interactions. Silicon Silicon is a covalent network solid and a semiconductor. Semiconductors allow us to control the flow of electricity through a circuit and provide the basis for modern electronics. Slide 79 / 163 Silicon form a 3-dimensional crystalline structure similar to diamond. It is a good thermal conductor and its ability to conduct electricity increases with temperature. Doping Impurities are introduced to silicon to alter its conductive behavior; this is referred to as doping. Slide 80 / 163 When an element with more valence electrons, such as phosphorus or arsenic, is added to silicon the additional electrons increase the semiconductor's electron carrier concentration. This makes the silicon an n-type (negative charge carrying) semiconductor. When an element with less valence electrons, such as boron or aluminum, is added to silicon the element accepts electrons from the silicon. This makes the silicon a p-type (positive charge carrying) semiconductor.

39 38 Diamonds are harder than graphite because... Slide 81 / 163 A they are made from different elements B they form different numbers of bonds C they are different types of compounds D they have different bond lengths 38 Diamonds are harder than graphite because... Slide 81 () / 163 A they are made from different elements B they form different numbers of bonds B C they are different types of compounds D they have different bond lengths 39 Covalent network solids do not conduct electricity. Slide 82 / 163 True False

40 39 Covalent network solids do not conduct electricity. Slide 82 () / 163 True False False 40 What effect would added gallium to silicon have? Slide 83 / 163 A reduce its conductivity B make it an n-type semiconductor C make it a p-type semiconductor D it would have no effect 40 What effect would added gallium to silicon have? Slide 83 () / 163 A reduce its conductivity B make it an n-type semiconductor C C make it a p-type semiconductor D it would have no effect

41 Properties of Molecular Compounds Since these substances are made up of lots of small molecules they behave differently than covalent network compounds. Slide 84 / 163 Non-conductive - because they are made of non-metallic atoms molecular compounds are excellent insulators Low melting points - molecules are small and held together by weak intermolecular forces (not bonds), these are easy to break giving molecular solids low melting and boiling points. weak inter-molecular forces between molecules 41 Butter melts on a hot day. What type of compound is it? Slide 85 / 163 A metallic B ionic C covalent network D molecular 41 Butter melts on a hot day. What type of compound is it? Slide 85 () / 163 A metallic B ionic C covalent network D D molecular

42 42 You are given a substance that has a high melting point and does not conduct electricity, even when you put it in water. What is it? Slide 86 / 163 A a metal B an ionic compound C a covalent network D a molecule 42 You are given a substance that has a high melting point and does not conduct electricity, even when you put it in water. What is it? Slide 86 () / 163 A a metal B an ionic compound C a covalent network D a molecule C 43 An unknown white powder is found to melt at 186oC. Identify the compound. Slide 87 / 163 A sugar B table salt C sodium bicarbonate D pewter

43 43 An unknown white powder is found to melt at 186oC. Identify the compound. Slide 87 () / 163 A sugar B table salt C sodium bicarbonate D pewter A Chemical Bonds Slide 88 / 163 ow ionic or covalent a bond is depends on the difference in electronegativity. The smaller the difference, the more likely electrons are "shared" and the bond is considered covalent, the greater the difference, the more likely electrons have been transferred and the atoms are ionized resulting in an ionic bond. Li Be B C N F Electronegativity Bond Li-F Be-F B-F C-F N-F - F-F Electronegativity Increasing Covalent Character Chemical Bonds While bond character (between ionic and covalent) is a spectrum, we can make a few simplifications... Slide 89 / 163 Ionic bonds occur when the difference in electronegativity between two atoms is 1.7 or greater. Na ---- F electronegativity = 3 If the difference of electronegativity is less than 1.7, it is a covalent bond. Neither atom takes electrons from the other; they share electrons. This type of bonding typically takes place between two nonmetals Cl electronegativity = 1.1 Click here to review naming covalent compounds

44 Slide 90 / 163 Slide 90 () / 163 Slide 91 / 163

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46 Covalent Bond Formation The sharing of electrons allows atoms to lower their potential energy by achieving a complete valence shell. Slide 93 / 163 Consider F 2 e- + e- + Click here to view an interactive [Ne] [Ne] Shared pair of electrons provides both fluorine atoms with a full valence shell (electrons are of opposite spin to minimize repulsions) Covalent Bond Formation Slide 94 / 163 The electronegativity difference between the atoms involved determines how equally the electrons are shared. Non-polar covalent bond - There is no difference in electronegativity so the electrons are shared equally. Polar covalent bond partially + -Cl partially - There is a significant difference in electronegativity between the atoms ( ) so the bond is polar, meaning opposite charges develop across the bond 47 Which of the following would be considered a polar covalent bond? Slide 95 / 163 A - B -S C Cl-Cl D C-S E C-

47 47 Which of the following would be considered a polar covalent bond? Slide 95 () / 163 A - B -S C Cl-Cl D C-S E C- E 48 Which of the following elements, if bonded to S would produce the most polar covalent bond? Slide 96 / 163 A B P C Cl D F E C 48 Which of the following elements, if bonded to S would produce the most polar covalent bond? Slide 96 () / 163 A B P C Cl D F E C D

48 Covalent Bond Strength The strength of a covalent bond is influenced by the radii of the atoms, the polarity of the bond, and by the # of electron pairs being shared. Slide 97 / 163 Effect of Atomic Radii Smaller atoms result in smaller distances between charges thereby increasing the Coulombic attractions Bond Atomic Radii Bond Enthalpy - = 53 pm 436 kj/mol Cl-Cl Cl = 79 pm 243 kj/mol Covalent Bond Strength Slide 98 / 163 Effect of Polarity The more polar the bond, the stronger the Coulombic attractions Bond EN difference Bond Enthalpy -Cl kj/mol -S kj/mol Note: The sizes are not a constant in this comparison, however, the projected enthalpy of an -Cl bond would be the average of an - and a Cl-Cl bond or 340 kj/mol. The observed enthalpy is much higher and is explained by the polarity of the bond. Covalent Bond Strength Slide 99 / 163 Effect of Multiple Shared Pairs Atoms often share more than one pair of electrons to realize a full valence shell. As we will learn later, these pairs do not all form the same kind of bonds but the net effect is to increase the Coulombic attractions between the nuclei. Bond # of shared pairs Bond Enthalpy kj/mol = kj/mol

49 49 As the number of bonds between a pair of atoms increases, the strength of the bond between the atoms: Slide 100 / 163 A increases B decreases C remains unchanged D varies, depending on the atoms 49 As the number of bonds between a pair of atoms increases, the strength of the bond between the atoms: Slide 100 () / 163 A increases B decreases C remains unchanged D varies, depending on the atoms A [This object is a pull tab] 50 Which of the following bonds would be expected to have the smallest bond enthalpy? Slide 101 / 163 A F-F B Cl-Cl C C-C D C-

50 50 Which of the following bonds would be expected to have the smallest bond enthalpy? Slide 101 () / 163 A F-F B Cl-Cl C C-C D C- B 51 Which of the following bonds would be expected to have the highest bond enthalpy? Slide 102 / 163 A F-F B - C C- D C- 51 Which of the following bonds would be expected to have the highest bond enthalpy? Slide 102 () / 163 A F-F B - C C- D C- B

51 Covalent Bond Length Slide 103 / 163 The length of a covalent bond is influenced by enthalpy of the bond. A high bond enthalpy is an indication of a strong coulombic attraction between nuclei, thereby indicating a small bond length between nuclei. Bond Enthalpy Length kj/mol 74 pm -Cl 431 kj/mol 127 pm C-C 347 kj/mol 154 pm C=C 611 kj/mol 121 pm Note: The C=C is longer than the - bond despite having the higher bond enthalpy due to the increased radii of the C atoms over the atoms in the - bond. 52 Which of the following would be expected to have the longest bond length? Slide 104 / 163 A - B -S C -Cl D -C 52 Which of the following would be expected to have the longest bond length? Slide 104 () / 163 A - B -S C -Cl D -C B

52 53 All else being equal, the more polar the bond, the shorter the bond length. Slide 105 / 163 True False 53 All else being equal, the more polar the bond, the shorter the bond length. Slide 105 () / 163 True False True 54 As the number of bonds between a pair of atoms increases, the distance between the atoms: Slide 106 / 163 A increases B decreases C remains unchanged D varies, depending on the atoms

53 54 As the number of bonds between a pair of atoms increases, the distance between the atoms: Slide 106 () / 163 A increases B decreases C remains unchanged D varies, depending on the B atoms [This object is a pull tab] Lewis Structures A proper Lewis structure distributes the valence electrons in the molecule so each atom has a full valence shell. Slide 107 / 163 Guidelines for writing Lewis structures Guideline ne: Determine the ordering of atoms in the molecule Typically, the least electronegative atom is the central atom. Cl CCl 4 Cl C Cl S 2 S Cl But not always... often it's the less abundant atom 2 N 3 N Lewis Structures Slide 108 / 163 Guidelines for writing Lewis structures Guideline Two: Determine the number of valence electrons in the molecule N 3 = 8 CCl 3 = 26 If the molecules is an ion, one must either subtract or add electrons to the valence electron count. N 3 - = = 24 N 4 + = 9-1 = 8

54 Lewis Structures Slide 109 / 163 Guidelines for writing Lewis structures Guideline Three: Form a single bond (2 shared electrons) between all elements and then distribute electrons such that all atoms have a full valence shell, saving the central atom for last. Example: 2 (8 ve) - - Example: C 2 (16 ve) - C - Notice needs only 2 electrons for a full valence shell. Notice that C does not have a full valence shell and therefore adjustments will need to be made to this structure Lewis Structures: ctet Rule The "ctet Rule" refers to the fact that a full valence shell for most elements is a full outer s and p orbital or 8 electrons. Some elements do not follow this as shown below. Slide 110 / 163 = 2 Be = 4 B = 6 In addition, elements in period 3 or below can have expanded octets or more than 8 valence electrons. Lewis Structures Slide 111 / 163 Guidelines for writing Lewis structures Guideline Four: If an atom is short of an octet, additional electrons must be shared between the nuclei forming pi bonds. - C - C Pi bonds Note: Pi bonds are formed from valence electrons in "p" orbitals.

55 Lewis Structures Slide 112 / 163 Guidelines for writing Lewis structures Guideline Five: If all atoms have a full valence shell but valence electrons remain, they are to be added to the central atom in pairs. F F S F 34 valence electrons F Extra pair of un-bonded electrons is added to central atom. 55 Diatomic Elements Students type their answers here Seven elements in the periodic table are always diatomic. In their elemental state, they are always seen as two atoms covalently bonded together. Slide 113 / 163 Which of these diatomic elements contains pi bonds? 2, 2, N 2, Cl 2, Br 2, I 2, F 2 N F Cl Br I 55 Diatomic Elements Students type their answers here Seven elements in the periodic table are always diatomic. In their elemental state, they are always seen as two atoms covalently bonded together. Slide 113 () / 163 Which of these diatomic elements contains pi bonds? 2, 2, N 2, Cl 2, Br 2, I 2, F N 2 2 and 2 N F Cl Br I [This object is a pull tab]

56 Practice C 4 Slide 114 / 163 I Elements Cl C Bonds & Electrons Practice C 4 Slide 114 () / 163 I Elements Cl C Bonds & Electrons C [This object is a pull tab] Practice N 2 Slide 115 / 163 I Elements Cl C N Bonds & Electrons

57 Practice N 2 Slide 115 () / 163 I Elements Cl C N Bonds & Electrons N N [This object is a pull tab] Practice C Slide 116 / 163 I Elements Cl C N Bonds & Electrons Practice C Slide 116 () / 163 I Elements Cl C N Bonds & Electrons C [*] Note: the 3rd bond in this structure is know as a coordinate covalent bond because both electrons are contributed from a single atom, the oxygen. [This object is a pull tab]

58 Practice S 4 2- Slide 117 / 163 I Elements Cl C N S For Ions + - Bonds & Electrons Practice S 4 2- Slide 117 () / 163 I Elements Cl C N S For Ions + - Bonds & Electrons [This object is a pull tab] Practice 3 + Slide 118 / 163 I Elements Cl C N S For Ions + - Bonds & Electrons

59 Practice 3 + Slide 118 () / 163 I Elements Cl C N S For Ions + - Bonds & Electrons + [This object is a pull tab] Practice SF 6 Slide 119 / 163 F Elements I Cl C N S Bonds & Electrons Practice SF 6 Slide 119 () / 163 F Elements I Cl C N S Bonds & Electrons [This object is a pull tab]

60 Practice XeF 4 Slide 120 / 163 F Elements Xe I Cl C N S Bonds & Electrons Practice XeF 4 Slide 120 () / 163 F Elements Xe I Cl C N S Bonds & Electrons [This object is a pull tab] 56 Which of the following elements is not diatomic in its elemental state? Slide 121 / 163 A Br 2 B S 2 C I 2 D 2

61 56 Which of the following elements is not diatomic in its elemental state? Slide 121 () / 163 A Br 2 B S 2 C I 2 D 2 B [This object is a pull tab] 57 Which of the following is the correct Lewis Structure for 2? Slide 122 / 163 A B C D 57 Which of the following is the correct Lewis Structure for 2? Slide 122 () / 163 A B C D D [This object is a pull tab]

62 58 Which of the following is the correct Lewis Structure for P 3? Slide 123 / 163 A B C D P P P P 58 Which of the following is the correct Lewis Structure for P 3? Slide 123 () / 163 A P B C D P P P B [This object is a pull tab] 59 Which of the following is the correct Lewis Structure for C 2 6? A C C B C C Slide 124 / 163 C C C D C C

63 59 Which of the following is the correct Lewis Structure for C 2 6? A C C B C C B Slide 124 () / 163 C C C D [This object is a pull tab] C C 60 Which of the following molecules would have 10 valence electrons in the Lewis structure? Slide 125 / 163 A N 4+ B CN- C 2 D N 2-60 Which of the following molecules would have 10 valence electrons in the Lewis structure? Slide 125 () / 163 A N 4+ B CN- C 2 D N 2- B

64 61 ow many valence electrons can be used in the Lewis stru for N +? Slide 126 / ow many valence electrons can be used in the Lewis stru for N +? Slide 126 () / Which of the following molecules has a central atom with an expanded octet? Slide 127 / 163 A S 2 B SCl 2 C PF 3 D XeF 2

65 62 Which of the following molecules has a central atom with an expanded octet? Slide 127 () / 163 A S 2 B SCl 2 C PF 3 D XeF 2 D 63 Which of the following molecules would require pi bonds in the Lewis structure? Slide 128 / 163 A I only B II only I. N 3 - II. C 3 2- III. CN C III only D I, II, and III 63 Which of the following molecules would require pi bonds in the Lewis structure? Slide 128 () / 163 A I only B II only I. N 3 - II. C 3 2- III. CN C III only D I, II, and III D

66 64 ow many unbounded pairs of electrons are on the central atom in Cl 3-? Slide 129 / ow many unbounded pairs of electrons are on the central atom in Cl 3-? Slide 129 () / Which of the following molecules would have a Lewis structure most similar to C 2? Slide 130 / 163 A S 2 B CS 2 C N 2 - D C 3 2-

67 65 Which of the following molecules would have a Lewis structure most similar to C 2? Slide 130 () / 163 A S 2 B CS 2 C N 2 - D C 3 2- B 66 Below is a skeleton for the Lewis structure for alphaketoglutarate, a Kreb's cycle intermediate. After finishing the lewis structure, how many pi bonds are needed to complete the structure? Slide 131 / 163 C - C - C - C - C 66 Below is a skeleton for the Lewis structure for alphaketoglutarate, a Kreb's cycle intermediate. After finishing the lewis structure, how many pi bonds are needed to complete the structure? Slide 131 () / 163 C - C - C - C - C 3

68 67 Which of the following would contain the largest number of pi bonds? Slide 132 / 163 A C 4 B C 3 2- C C 2 2 D SF 6 67 Which of the following would contain the largest number of pi bonds? Slide 132 () / 163 A C 4 2- B C 3 C C 2 2 D SF 6 C 68 Which of the following is the correct Lewis structure for the ammonium ion? Slide 133 / 163 A B N + N C N D N

69 68 Which of the following is the correct Lewis structure for the ammonium ion? Slide 133 () / 163 A B N N + B C N D N [This object is a pull tab] Resonance Structures Slide 134 / 163 When pi bonds can be formed in more than one location, the electrons are thought to be shared across all of the possible locations. This is shown by writing resonance structures. N ne pi bond is needed but could be formed from electrons shared by any of three oxygens. Resonance structures N N N Resonance Structures Slide 135 / 163 The bonds involved in resonance are equivalent in strength and in length. In essence, the pi bond electrons are shared across all of the bonds in which we find resonance. N N N EQUALS N Pi bond electrons shared across all three bonds.

70 Practice S 3 Slide 136 / 163 I Elements Cl C N S Bonds & Electrons Practice S 3 Slide 136 () / 163 I Elements Cl C N S Bonds & Electrons [This object is a pull tab] Practice N 3 - Slide 137 / 163 I Elements Cl C N S For Ions + - Bonds & Electrons

71 Practice N 3 - Slide 137 () / 163 I Elements Cl C N S For Ions + - Bonds & Electrons [This object is a pull tab] 69 Which of the following show the correct Lewis structure for 3? A Slide 138 / 163 B C D Both A & C 69 Which of the following show the correct Lewis structure for 3? A Slide 138 () / 163 B C D D Both A & C [This object is a pull tab]

72 70 Which of the following molecules demonstrate resonance structures? Slide 139 / 163 A I only B II only I. N 2 - II. C 3C- (both attached to C) III. C 3C 2 C III only D I and II only 70 Which of the following molecules demonstrate resonance structures? Slide 139 () / 163 A I only B II only C III only D I and II only I. N - 2 II. C 3C- (both attached to C) III. C 3C 2 D 71 ow many resonance structures would be needed to represent S 3? Slide 140 / 163

73 71 ow many resonance structures would be needed to represent S 3? Slide 140 () / All bonds that demonstrate resonance are equal in length but not in strength. Slide 141 / 163 True False 72 All bonds that demonstrate resonance are equal in length but not in strength. Slide 141 () / 163 True False False

74 73 The C- bonds in the carbonate ion (C 3 2- ) would consist of A 3 single bonds Slide 142 / 163 B 2 single bonds of longer length and 1 double bond of shorter length C 3 double bonds D 3 bonds equal in length but shorter than a single bond 73 The C- bonds in the carbonate ion (C 3 2- ) would consist of A 3 single bonds Slide 142 () / 163 B 2 single bonds of longer length and 1 double bond of shorter length C 3 double bonds D 3 bonds equal in length but shorter than a single bond D 74 Which of the following require no resonance structures to represent? Slide 143 / 163 A N + B S 2 C C 3C (both attached to C) D N 3-

75 74 Which of the following require no resonance structures to represent? Slide 143 () / 163 A N + B S 2 C C 3C (both attached to C) D N 3- A Formal Charge Slide 144 / 163 The formal charge tells us how the electrons are distributed within a molecule. For example, depending on how the electrons are shared, some atoms may have more electrons than others resulting in a semicharged state for that atom. Formal Charge = # of valence electrons - # of electrons atom possesses within the lewis structure. P FC for P: 5-4= +1 (count each bond as one) FC for each : 6-7= -1 (count each bond as one) Note: The charges must add to the charge of the molecule. So for P P atom x +1 = atoms x -1 = = -3 Formal Charge Slide 145 / 163 The best Lewis structure will have the formal charge = 0 on each atom. owever, if the molecule carries a charge, the more electronegative atoms should carry a charge as they have the greater attraction for electrons. [ - ] -1 FC on = 6-7 = -1 FC on = 1-1 = 0 Each bond is counted as one in a formal charge calculation as each atom forming part of the bond contributes just one electron to that bond. The oxygen is more electronegative so it makes sense that it carries the negative charge.

76 Formal Charge Slide 146 / 163 Example: Below are two possible Lewis structures for the phosphate ion, P Which Lewis structure is considered to more closely represent the actual molecule based on formal charge calculations? P P Structure 1 Structure 2 (exhibits resonance) Structure 2 is superior because the formal charges on each atom = 0 whereas in structure 1, the P carries a +1 charge and each oxygen carries a -1 charge slide for answer 75 What is the formal charge on the S atom in the molecule depicted below? Slide 147 / What is the formal charge on the S atom in the molecule depicted below? Slide 147 () / 163 2

77 76 What is the formal charge on the atom in the molecule depicted below? Slide 148 / What is the formal charge on the atom in the molecule depicted below? Slide 148 () / What is the formal charge on the indicated N atom in the molecule below? Slide 149 / 163 N N N Note: When multiple resonance structures can be written, the structure with the formal charges closest to zero is most stable.

78 77 What is the formal charge on the indicated N atom in the molecule below? Slide 149 () / 163 N N N -2 Note: When multiple resonance structures can be written, the structure with the formal charges closest to zero is most stable. Bond rder The bond order refers to the number of bonds between two atoms in a molecule. It is calculated by adding up the bonds attached to the atom divided by the number of atoms attached to that atom. The higher the bond order, the stronger and shorter the bond. Slide 150 / 163 N Bond order of N- bonds = 4/3 = 1.33 N N Bond order of N-N bond = 3/1 = 3 78 Which of the following contains bonds of the lowest order? Slide 151 / 163 A N 2 B S 2 C S 3 D CF 4

79 78 Which of the following contains bonds of the lowest order? Slide 151 () / 163 A N 2 B S 2 C S 3 D CF 4 D 79 Which of the following would have a bond order of 1.5? Slide 152 / 163 A C 3 2- B N 2 - C C 2 D CS 2 79 Which of the following would have a bond order of 1.5? Slide 152 () / 163 A C 2-3 B N - 2 C C 2 D CS 2 B