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  • Audio 0:00:20.125734
  • Homework issue
    • Electron configurations
      • There are differences sometimes in the order of writing them.
      • You get five or six freebies
        • If you’ve checked the electron configuration and it says you’re wrong, it may be the way the website works.
  • Audio 0:02:01.735946
  • Real world is complicated
    • He isn’t going to tell us anything that is wrong but everything we’re learning is a really watered-down, simplified version of the truth

Energetics of Ionic Bond Formation: Using NaCl as an Example

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    • Where we left off The ionization energy of the metal is endothermic.
  • The electron affinity of the nonmetal is exothermic.
  • Generally, the ionization energy of the metal is larger than the electron affinity of the nonmetal; therefore, the formation of the ionic compound should be endothermic.
  • But the heat of formation of most ionic compounds is exothermic and generally large.

Crystal Lattice and Lattice Energy of NaCl

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    • Part of the energy formula in the previous slide does not add up because it does not account for the lattice shape of the compound
  • Lattice energy
    • The extra stability that accompanies the formation of the crystal lattice is measured as the lattice energy.
      • Audio 0:07:54.475155
    • It is the energy released when the solid crystal forms from separate ions in the gas state.
      • Always exothermic
    • Lattice energy is measured directly but is calculated from knowledge of other processes.
    • It depends directly on the size of charges and inversely on distance between ions.
    • (Coulomb’s law)
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    • The most stable lattice is a very difficult calculation

Ionic Bonding Model versus Reality

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  • implies that the positions of the ions in the crystal lattice are critical to the stability of the structure.
  • predicts that moving ions out of position should therefore be difficult, and ionic solids should be hard.
    • Ionic solids are relatively hard compared to most molecular solids.
      • If you’ve ever touched a crystal, this is obvious
  • implies that if the ions are displaced from their position in the crystal lattice, repulsive forces should occur.
    • this predicts that the crystal will become unstable and break apart. Theory predicts that ionic solids will be brittle.
      • If you strike a crystal with a hammer, it will shatter because it becomes unstable
        • The same is not true for metals
      • Ionic solids are brittle. When struck, they shatter.
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  • implies that, in the ionic solid, the ions are locked in position and cannot move around.
  • predicts that ionic solids should not conduct electricity.
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    • To conduct electricity, a material must have charged particles that are able to flow through the material.
    • Ionic solids do not conduct electricity.
  • implies that, in the liquid state or when dissolved in water, the ions will have the ability to move around. predicts that both a liquid ionic compound and an ionic compound dissolved in water should conduct electricity.
    • Ionic compounds conduct electricity in the liquid state or when dissolved in water.

Conductivity of NaCl

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  • In NaCl(s), the ions are stuck in position and not able to move to the charged rods.
  • In NaCl(aq), the ions are separated and are able to move to the charged rods.

Ionic Bonding and the Crystal Lattice

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  • The extra energy that is released comes from the formation of a structure in which every cation is surrounded by anions and vice versa.
    • This structure is called a crystal lattice.
  • The crystal lattice is held together by the electrostatic attraction of the cations for all the surrounding anions.
    • Electrostatic attraction is a nondirectional force.
      • Therefore, there is no ionic molecule.
        • The chemical formula is an empirical formula, simply giving the ratio of ions based on charge balance.
  • The crystal lattice maximizes the attractions between cations and anions leading to the most stable arrangement

Ionic Compounds

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  • Ionic compounds are composed of cations (metals) and anions (nonmetals) bound together by ionic bonds.
    • Examples of ionic compounds:
      • NaBr, Al2(CO3)3, CaHPO4, and MgSO4
  • The basic unit of an ionic compound is the formula unit, the smallest, electrically neutral collection of ions.
    • Example:
      • The ionic compound table salt, with the formula unit NaCl, is composed of Na+ and Cl+ions in a one-to-one ratio.
  • Summarizing Ionic Compound Formulas
    • Ionic compounds always contain positive and negative ions.
    • In a chemical formula, the sum of the charges of the positive ions (cations) must equal the sum of the charges of the negative ions (anions).
    • The formula of an ionic compound reflects the smallest whole-number ratio of ions.

Nomenclature: Naming Compounds

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  • Organic compounds: predominantly carbon Usually plus H, O, N, S
  • Inorganic compounds: everything else

  • Ionic Compounds: Cation followed by anion +-ide ## Naming Ionic Compounds

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  • Ionic compounds can be categorized into two types, depending on the metal in the compound.
  • The first type contains a metal whose charge is invariant from one compound to another.
  • Whenever the metal in this first type of compound forms an ion, the ion always has the same charge.
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  • Metals with invariant charges
  • common nonmetal anions

Naming Binary Ionic Compounds of Type I Cations

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  • Binary compounds contain only two different elements. The names of binary ionic compounds take the following form:
  • For example, the name for KCl consists of the name of the cation, potassium, followed by the base name of the anion, chlor, with the ending -ide.
    • KCl is potassium chloride.
      • We know potasium is +1, we know Cl is -1, so we don’t have to write it
  • The name for CaO consists of the name of the cation, calcium, followed by the base name of the anion, ox, with the ending -ide.
    • CaO is calcium oxide.

Chemical Nomenclature

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  • Ionic Compounds
    • often a metal + nonmetal
    • anion (nonmetal), add “ide” to element name

Clicker 1

  • Write the formula for calcium nitride
    • Ca_3N_2

Lewis Structure Model: Representing a Substance’s Valence Electrons

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  • The Lewis Model:
    • Valence electrons are represented as dots.
  • Lewis electron-dot structures (Lewis structures) depict the structural formula with its valence electrons.
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  • Lewis structures focus on valence electrons because chemical bonding involves the transfer or sharing of valence electrons between two or more atoms.

Octet Rule: A Guideline for Molecule Formation

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  • When atoms bond, they tend to gain, lose, or share electrons to give a noble gas–like configuration.
    • ns2np6
  • Nonmetals: period 2 elements must obey the octet rule (i.e., eight valence electrons around each atom in the molecule).
  • Exceptions to the octet rule: Expanded octets
    • (Sometimes octet rule doesn’t work)
    • Audio 0:29:09.248458
    • They involve the nonmetal elements located in period 3 and below.
    • Nonmetals (period 3 on down in the periodic table) follow the octet rule when they are not the center atom.
      • The center atom is the atom in the molecule that the other elements individually bond (attach) to.
    • When they are the center atom, they can accommodate more than eight electrons.
  • Using empty valence d orbitals that are predicted by quantum theory

Multivalent Metals: Naming Type II Ionic Compounds

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  • The metals in this category tend to have multiple charges (i.e., multivalent cations):
  • Their charge cannot be predicted as in the case of most representative elements and must be noted in their name.
  • Transition and inner transition metals
    • Iron (Fe) forms a 2+ cation in some of its compounds and a 3+ cation in others.
      • FeSO4: Here iron is a +2 cation (Fe2+).
      • Fe2(SO4)3: Here iron is a +3 cation (Fe3+).
  • Many of the p-block metals
    • Not all p-block metals are multivalent.
    • Some main-group metals, such as Pb, Tl, and Sn, form more than one type of cation.

Type II Cation

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Naming Type II Binary Ionic Compounds— Example: CrBr3

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  • To name CrBr_3, cation + total anion charge = 0
    • Cr charge + 3(Br+charge) = 0
    • Since each Br has a –1 charge, then
      • Cr charge + 3(–1) = 0
      • Cr charge + (–3) = 0
      • Cr = +3
    • Hence, the cation Cr3+ is called chromium(III), and Br^- is called bromide.
  • The name for CrBr3 is chromium(III) bromide.

Polyatomic Ions

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Oxyanions

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  • Most polyatomic ions are oxyanions, anions containing oxygen and another element.
  • Noticethatwhenaseriesofoxyanionscontainsdifferent numbers of oxygen atoms, the oxyanions are named according to the number of oxygen atoms in the ion.
  • Iftherearetwoionsintheseries,
    • the one with more oxygen atoms has the ending -ate; and +the one with fewer has the ending -ite.
  • Forexample,
    • NO3+is nitrate SO_4^2+ is sulfate
    • NO2+is nitrite SO_3^2+ is sulfite
  • If there are more than two ions in the series, then the prefixes hypo-, meaning less than, and per-, meaning more than, are used.

Naming Ionic Compounds Containing Polyatomic Ions

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  • Ionic compounds that contain a polyatomic ion rather than a simple anion (e.g., Cl–) are named in the same manner as binary ionic compounds, except that the name of the polyatomic ion used.
    • For example, NaNO2 is named according to
      • its cation, Na+, sodium; and
      • its polyatomic anion, NO2–, nitrite.
    • Hence, NaNO2 is sodium nitrite.

Common Polyatomic Ions

    • You should memorize this

Chemical Nomenclature

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  • Ionic Compounds/Polyatomic Anion
  • BaSO4 barium sulfate
  • KMnO4 potassium permanganate Mg(OH)2 magnesium hydroxide
  • KNO3 potassium nitrate
  • (NH4)3PO4 ammonium phosphate

Clicker 2

  • Copper(II) phosphate’s formula
    • Cu_3(PO_4)2

Hydrated Ionic Compounds

  • Audio 0:44:52.355986
  • Hydrates are ionic compounds containing a specific number of water molecules associated with each formula unit.
  • Some ionic compounds have multiple hydrates

Hydrates

  • Common hydrate prefixes
    • hemi = 1⁄2
    • mono = 1
    • di = 2
    • tri=3
    • tetra = 4
    • penta = 5
    • hexa = 6
    • hepta = 7
    • octa = 8
  • Other common hydrated ionic compounds and their names are as follows:
    • CaSO4 +1⁄2H2O is called calcium sulfate hemihydrate.
    • BaCl2 +6H2O is called barium chloride hexahydrate.
    • CuSO4 +6H2O is called copper sulfate hexahydrate.

Vocab

Term Definition
lattice energy the extra stability that accompanies the formation of the crystal lattice
ionic solid properties relatively hard and brittle and don’t conduct electricity
crystal lattice structre in which every cation is surrounded by anions and vice versa
binary compounds compounds containing only two different elements
formula unit empirical formulla of any ionic compound which is the lowest whole number ratio of ions
oxyanions anions containing oxygen and another element
acetate formula C_2H_3O_2^-
carbonate CO_3^2-
hydrogen carbonate HCO_3^-
hydroxide OH^-
nitrite NO_2^-
chromate CrO_4^2-
dichromate Cr_2O_7^2-
phosphate PO_4^3-
hydrogen phosphate HPO_4^2-
dihydrogen phosphate H_2PO_4^-
ammonium NH_4^+
hypochlorite ClO^-
chlorite ClO_2^-
chlorate ClO_3^-
perchlorate ClO_4^-
permanganate MnO_4^-
sulfite SO_3^2-
hydrogen sulfite HSO_3^-
sulfate SO_4^2-
hydrogen sulfate HSO_4^-
cyanide CN^-
peroxide O_2^2-
hydrates ionic compounds containing a specific number of water molecules associated with each formula unit