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Section 1A
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Bonding II: Types of substances
1) Ionic compounds = continuous Ionic bonding between weak loser metal and strong gainer nonmetal ex: NaCl Sodium Chloride
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Honors: Traditional system for Ionic
Latin suffix with endings -ic (higher charge) or –ous (lower Charge) Ex: copper +1 OR +2 oxidation states Copper (I) oxide Copper (II) oxide Cu2O CuO Cuprous oxide cupric oxide Others: Ferrous / Ferric Fe = iron Stannous / Stannic Sn = tin plumbous / plumbic Pb = lead What is the formula for ferrous chloride? FeCl2
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Bonding II: Types of substances
1) Ionic compounds = continuous Ionic bonding between weak (loser) metal and strong (gainer) nonmetal 2) molecular compounds = covalent bonding inside molecules = IM forces between molecules between strong nonmetals ex: SO2 Sulfur (IV) oxide Organics – with Carbon ex: CH4 methane Acids – with H as the loser ex: HCl hydrogen chloride
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Organic molecular compounds (vs. inorganic)
- Based on chain of carbon with H and other nonmetals attached. Many molecular formulas can be reduced (simplified) to empirical (ratio) formulas Ex: glucose molecular formula: C6H12O6 empirical formula: CH2O 6:12:6 = 1:2:1 ratio 6
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Problem: What is the empirical formula for the molecular formula C6H8?
6:8 = 3:4 ratio 2 C3H4
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Hydrogen compounds Hydrogen sulfide Hydrogen sulfate Water
H+ forms molecular (covalent) compounds with other nonmetals. named like ionic compounds when in their pure state ex: HCl hydrogen chloride others: 1. H2S 2. H2SO4 3. H2O 4. H2O2 Hydrogen sulfide Hydrogen sulfate Water Hydrogen Peroxide H- in back are hydrides Ex: Metal hydrides KH potassium hydride [O2]2- polyatomic ion (Sodium peroxide = Na2O2)
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Acids: H+ compounds (aq) in water
Has properties of both ionic and molecular Made of molecules, but can break into ions in water Ex: HCl (g) → HCl (aq) = ( Separate H+ & Cl- ions ) H2O Hydrogen chloride Hydrochloric acid Unlike typical molecular compounds: acids are Gases and liquids that are soluble in water Solutions conduct electricity like ionic
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NaCl (aq) C6H12O6 (aq) HCl (aq) ?
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Acids w/ H in front Or COOH at end
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Bonding II: Types of substances
1) Ionic compounds = continuous Ionic bonding 2) molecular compounds = covalent bonding inside molecules Organic – with Carbon Acids – turn ionic in water 3) Network substances = continuous covalent bonding - C and Si Crystals - Elements that form 4 bonds (bonds in all directions)
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Network Solids: Molecular: Discrete Particles Ex: H2O | | |
Continuous covalent bonds Hard, very high melting points Elements which form 4 bonds Ex: diamond (C), Sand (SiO2) | | | --- C --- C --- C --- | | | | | | Weak forces Between molecules = Low MP
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Bonding II: Types of substances
1) Ionic compounds = continuous Ionic bonding 2) molecular compounds = covalent bonding inside molecules 3) Network substances = continuous covalent bonding 4) Metallic (pure and mixtures – alloys) continuous metallic bonds
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Learning Check: What are the four types of pure “substances”
How can bonding type be surmised from the chemical formula of a substance? What identifies a compound as organic? Is the formula H2O an empirical or molecular formula? What identifies a substance as an acid? How is it different from other molecular substances? What kind of bonding is in a network structure? How is it different from molecular structures?
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Section 1B
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Polarity in covalent (sharing) bonds
Bond Polarity: Balance of charge in bonding is due to the difference in pull on electrons (atoms don’t share equally) No polarity Polar bond Atoms of same element BrINClHOF’s Bond is nonpolar Atoms of different elements Electrons pulled toward stronger atom. Bond is “polar”
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Problems Same = nonpolar Different nonmetals Ionic, not covalent
Which contain molecules with polar covalent bonds? H2(g) HCl (g) CCl4(l) NaCl (s) Fe (s) Same = nonpolar Different nonmetals Ionic, not covalent Metallic bonds
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Electronegativity (pulling strength)
Ability of an atom to attract a pair of bonding electrons to itself Metals Weak Fr is Least Electro- Negative (“electro-positive”) Nonmetals Strong F is Most Electro- negative increasing decreasing
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some polarity in the bond Highest polarity is ionic bond
Bond “Character” Depends on difference in electronegativity between bonded atoms NaF HF OF F-F = 0 No polarity in the bond 4.0 – 2.1 = 1.9 high polarity in bond 4.0 – 3.5 = 0.5 some polarity in the bond 4.0 – 0.9 = 3.1 Highest polarity is ionic bond 100% covalent character Most ionic character Further apart = more polarity = more ionic character
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Bond “Character” NaF HF OF2 F-F 3.1 1.9 0.5 0.0
Difference in electronegativity between bonded atoms NaF HF OF F-F most polar fairly polar less polar no polarity Ionic character covalent character Ionic polar covalent nonpolar covalent
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Practice problems 2.1- 2.1 = 0.0 Strongest gainer With H 4.0- 2.1 =
1. Which bond is most polar? a. H-H b. H-F c. H-O d. H-I 2. Which substance has the greatest ionic character? a. C-Cl b. H-Cl c. Cl-Cl d. Na-Cl = 0.0 Strongest gainer With H = 1.9 1.4 0.6 (Greatest polarity) = 0.6 1.1 0.0 2.3 Only ionic compound!
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Section 1C
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Molecule Polarity Negative Positive Pole Pole Ex: H --- Cl
Due to symmetry of bonds, molecules can be polar or nonpolar A Polar molecule: Is called a Dipole” it has negative and positive poles (ends) Is Asymmetrical (not symmetrical) in molecule shape and not symmetrical in electron arrangement Electrons pulled toward stronger Cl end of molecule Dipoles are “sticky” Positive Pole Negative Pole Ex: H --- Cl molecules with different ends are Polar or “dipoles”
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Nonpolar Nonpolar Nonpolar Nonpolar = symmetrical, “balanced”
Polar = asymmetrical, “unbalanced” If it has a front, back, top or bottom its polar. If its symmetrical its Nonpolar Polar or nonpolar? Nonpolar Nonpolar Nonpolar
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Predicting Polarity (predicting shape)
Ne VSEPR Theory - used to predict the shape and polarity of molecules from Lewis electron dot structure (Valence Shell Electron Pair Repulsion) Four Electron pairs repel each other to the 4 corners of a tetrahedron arrangement Bonded atoms get arranged into different shapes Ex: H2O angular Tetrahedron Vesper Electron Pairs Act as Bonded atoms
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Polar shapes: asymmetrical charge shape and charge distribution
Linear Polar Ex: HF, HI, etc. Two different elements Angular (bent) polar Ex: H2O, OF2 x H x O F O F x I H x Angular Or straight? Why? (+) H --- I (--) (+) H --- O (--) | H (+)
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N H X H x Pyramid (Trigonal) Ex: NH3 Vesper electron pair
pushes other Atoms into a pyramid Shape!
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Nonpolar molecule shapes
Symmetrical shape and distribution of electron charge Look for C or Si in compounds Linear nonpolar Ex: BrINClHOF’s CO2, CS2 O=C=O All C’s electrons are in the bond No Vesper electron pair to push O x C Notice: nonpolar compounds usually contain C
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Tetrahedral molecules CH4 or CCl4
Structural formula Structural formula: each line = 2 electrons Notice: CX4
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Less common shapes: Trigonal Planer
Nonpolar BF3 Polar CH2O
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Learning check: Predict the shape of each molecule
and if it is Polar or Nonpolar: 1. O He 2. CCl N2 3. HCl OF2 4. H2O CH2F2 5. NF PCl3 6. CS NH4+
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Section 2A
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Intermolecular (“sticky”) forces
Called Vanderwaal’s forces (“IM” forces) Weak Physical force between adjacent molecules (ex: determines how high melting points will be) Affected by polarity (shape) of molecules (Negative pole attracted to positive pole) Allows molecular substances to exist as liquids and low melting point solids (instead of gases) Two types: dipole attractions and dispersion forces
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HF is more polar = stickier
Polar molecules (dipoles) are attracted to each other. Depends on extent of molecules polarity (ex: HCl vs. HF) Hydrogen bonds special type H bonded to small, strong atom: F, O, or N Found between molecules in HF, H2O, NH3 Accounts for higher than expected MP and BP “Dipole Attractions” HF is more polar = stickier H is a naked proton
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What kind of question is this:
Notice all have H bonded to another nonmetal Hydrogen bonding!
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Dispersion forces “Big and sticky force”
In large and Nonpolar molecules Random Dispersion of electrons creates temporary (+) and (-) poles Stronger in molecules with more electrons (larger) and as molecules get closer Ex: liquefaction of gases only at high pressure (molecules forced together) Ex: wax, dry ice (CO2(s)) “Big and sticky force” What explains the pattern of phases in group 17?
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Phase change / boiling point questions:
Usually relate to IM (sticky) forces Low temp = weak IM forces
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At STP, both at same temperature
46 At STP, fluorine is a gas and iodine is a solid. This observation can be explained by the fact that fluorine has (1) weaker intermolecular forces of attraction than iodine (2) stronger intermolecular forces of attraction than iodine (3) lower average kinetic energy than iodine (4) higher average kinetic energy than iodine gas = weaker IM forces F2 smaller than I2 Average Kinetic energy Ie. How fast molecules are moving = Temperature At STP, both at same temperature
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What IM forces are responsible?
Recall: Organics are mostly Nonpolar Acetone C3H6O Propane C3H8 Octane C8H18 Glycerol C3H4(OH)3
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IM force? Mostly dispersion forces Acetone C3H6O Acetone is the liquid in fingernail Polish remover that makes it dry quickly
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IM force? Mostly dispersion forces Propane C3H8 Propane is the gas used for heating many homes
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Glycerol is a viscous liquid used to make cake frosting creamy
IM force? some dispersion forces Notice the OH group? Hydrogen bonding! Glycerol C3H4(OH)3
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Octane is one of the liquids in gasoline
IM force? dispersion forces Octane C8H18
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Can you explain the trends?
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Practice problems: Which liquid contains the strongest intermolecular forces: He(l), Ne(l), Ar(l), Or Kr(l)? Why? 2. Which has the strongest Hydrogen bonds? H2, HF, HCl, or HBr? 3. Which is expected to have the lowest Boiling point? F2, Cl2, Br2, or I2? What two kind of bonds are found in a sample of H2O(l)?
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Boiling point questions: Usually relate to IM (sticky) forces
41 Based on intermolecular forces, which of these substances would have the highest boiling point? (1) He (3) CH4 (2) O2 (4) NH3 Polar / H-bonds = strongest IM forces, highest BP 23 Hydrogen bonding is a type of (1) strong covalent bond (2) weak ionic bond (3) strong intermolecular force (4) weak intermolecular force Oxymoron: Strongest of the weak forces!
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Each molecule listed below is formed by sharing electrons between atoms when the atoms within the molecule are bonded together. Molecule A: Cl2 Molecule B: CCl4 Molecule C: NH3 59 Explain why NH3 has stronger intermolecular forces of attraction than Cl2. [1] 60 Explain why CCl4 is classified as a nonpolar molecule [1] 61 Explain how the bonding in KCl is different from the bonding in A, B, and C [1]
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Section 2B
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Distinguishing between substances: Ionic compounds = Ionic bonding
molecular compounds = covalent bonding metallic – pure or alloys = metallic bonds Network substances = covalent bonding Based on properties: Melting or boiling point / phase Solubility in water Electrical conductivity
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Electrical conductivity
What is required to conduct electricity? Metals: yes as solid or liquid Ionic salts: no when solid, yes when (aq) in H2O or when fused (melted) into liquid Molecular – no, except acids when (aq) in water Requires particles which are: (1) charged AND (2) mobile Mobile electrons Mobile ions Mobile ions Electrolyte: substance that conducts electricity when dissolved in water Includes ionic salts and acids Ex: NaCl, HCl
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Metals w/ mobile electrons Molecular have Neutral molecules Ionic w/ mobile Ions when dissolved
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Ions in water Allow acids to Conduct electricity
Strong acids = lots of ions formed Weak acids = few ions formed
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Properties of solids Ionic molecular metallic network
Strong Weak Continuous strong Continuous intermolecular flexible continuous Ionic bonds forces metallic bonds covalent bonds Brittle solids soft solids malleable very hard High MP low MP MP varies extremely high MP Usually soluble not usually soluble NO NO In water in water solubility solubility Conductors: as (l) or (aq) Poor conductor good conductor poor conductor (mobile ions) (neutral particles) (mobile electrons) (nothing is mobile)
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Review problems What kind of Substance?
A white crystalline substance, conducts when dissolved in aqueous solution. A soft solid, melts at 75 0C. Nonconductor Silvery grey solid. Good electrical conductor Crystalline solid. Melts at 10000C. Nonconductor. White crystalline solid. Dissolves easily, but aqueous solution doesn’t conduct electricity
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Review problems: What kind of bond accounts for these properties? (Describe) White crystalline solid, melts at 7000C. Conducts electricity as a when fused (melted). A liquid, evaporates readily. A malleable solid. A sticky viscous liquid. Water’s high surface tension.
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Sample questions H with small e- gainer
High melting point = strong forces:
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Salts are soluble: ionic
Conducts e- when dissolved: ionic Strong bonds:
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Methane is CH4
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