Unit IV. Ionic Bonding 

reading Assignment 1: KTU & Read Ch. 7.1-7.2, Section questions 1-21

 

A. Atoms/Ions

  1. Atoms are electrically neutral- equal number of electrons and protons

  2. Ion- atoms which have either gained or lost electrons- contain a net charge due to imbalance between protons and electrons

    a. cation- electrically positive ion- due to a loss of electrons

    b. anion- electrically negative ion- due to a gain of electrons

 

review:  Quick Check for Understanding on atoms and ions

practice:: Finding the number of subatomic particles

 

  3. Valence shell- Highest energy level occupied by electrons

    a. Valence electrons- electrons in the valence shell

      1. Elements in the same groups usually have the same number of valence electrons

      2. The group number for representative elements is the same as the number valence electrons

   

    b. Electron dot structures or Lewis-Dot structures (G.N. Lewis)

      Lewis, G.N., The Atom and the Molecule, Journal of the American Chemical Society, 1916.

      -describes the valence electrons in an atom utilizing dots and symbols (x can be used to represent valence electrons

      especially when representing those involved in chemical bonds)

     -how to draw electron-dot structures

 

    c. Octet Rule- Atoms have a tendency to gain/lose electrons and achieve electron configurations of the noble gases

        First proposed by Irving Langmuir, 1919. The structure of atoms and the octet theory of valence, PNAS, 1919.

 

    d. Stable ion configurations- addition or subtraction of electrons from orbitals that yield electron configurations of the noble 

       gases.- pseudo-noble gas configurations

       Isoelectric species- atoms/ions that have similar electron configurations

 

    e. Oxidation Number- net charge of the stable ion

      -identifying oxidation states

 

Periodic Variations of Oxidation Numbers

1.

The maximum positive oxidation number for any representative element is equal to the group number, from +1 (Alkali metals) to +7 (Halogens). Noble Gases have an oxidation number of 0

2.

Metallic elements usually exhibit only positive oxidation numbers due to low Zeff values

3.

The most negative oxidation number for any representative element is equal to the group number minus eight.

4.

Negative oxidation numbers are commonly limited to nonmetals. Semi-metals are negative only when these elements are combined with less electronegative elements.

5.

Elements commonly exhibit positive oxidation numbers only when combined with more electronegative elements.

6.

With the exception of Carbon, Nitrogen, Oxygen, and Mercury, each representative element that exhibits multiple oxidation numbers in its compounds commonly have oxidation numbers that are either all even or all odd.

 

Assignment 1: Ions & oxidation states worksheet.

B. Compounds 

  1. Compound- a pure substance that is composed of two or more elements that are chemically bonded   

 

Tutorial: Introduction to Chemical Bonding.

 

  2. Law of Definite Proportions- All samples of the same compound contain the same elements in the same proportion by mass.

      Coined by Joseph Proust

     -John Dalton used this as a foundation to his Atomic Theory  

 

Calculating Percent Mass

Percent Mass   =Mass of the element  x 100%

             Mass of the sample

 

practice: Practice Problems involving percent mass calculations

 

    a. Law of Multiple Proportions.  When two elements reacts to form more than one compound, the ratios of the element's masses

       can be reduced to a small whole number. 

      Molecules- a group of atoms that are chemically bonded which act as an individual unit

      Typically formed from covalent bonds-

 

  3. Ionic Bond- a chemical bond that occurs by a transfer of electrons and the resulting electrostatic attraction between 

     the charged particles (ions)  

    a. Due to larger differences in electronegativities (metal/nonmetal)  

      -Electronegativity is the pull on electrons involved in a covalent bond. Derived by Linus Pauling (narrative)

   

 

Explanation: Bond types based on Electronegativities

 

    b. Ionic Compounds- Compounds formed from ionic bonds  

      Characteristics:  

      1. Brittle Crystalline Solids  

sdg

      2. High melting points- smaller ions produce higher melting points  

      3. Conduct electricity in the molten state (barring no decomposition)

      4. Dissolve in high-polarity solvents (H2O) which results in conduction of electricity- electrolyte  

      5. Lattice Energy- the energy associated with bonded ions in a crystal  

 

Calculating Lattice Energy

Lattice Energy    =  k   (qc  qa) 

                            d

q is the charge of the cation or anion  

d is the S of the ion radii (table of ionic radii)

 

      Lattice Energy is the energy needed to vaporize the ions in a compound.  This is basically related to the amount of energy

      that is released when the ions come together forming the compound.  

      Correlation of Melting Points and Lattice Energy of Sodium halide salts

 

      Special Note:  Forming ionic compounds is typically an exothermic process (releasing energy) because the ions are more

      stable in the crystal than being separated.

      ** As lattice energy increases → Solubility decreases & melting point increases **  

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Resource: Lattice energy can be indirectly calculated using the Born-Haber Cycle

Table:  Solubilities of Ionic Compounds. Print this off. 

 

Reading Assignment 2: KTU & Read Ch. 9.1 & 9.2: Questions 1, 2, 6-8, 10-15, 22, 24 & 26

 

    4.Chemical formula- shows that kinds and numbers of atoms in a compound  

      a. Empirical formula- shows the simplest whole-number ration of atoms in a molecule  

      b. Molecular formula- shows the actual ratio of elements in a molecule  

      c. Formula Unit- lowest whole-number ratio of ions in an ionic compound  

 

    5. Percent Ionic Character (Pauling)- Based on electronegativities differences (De.n.) between cations and anions

 

Percent Ionic Character of a Single Chemical Bond
D e.n 0.1 0.2 0.3 04 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2
% I.C 0.5 1 2 4 6 9 12 15 19 22 26 30 34 39 43 47 51 55 59 63 67 70 74 77 79 82 84 88 89 91 92 95

     

 a. Allen Factor (Leland C. Allen- Princeton)- used to predict Percent Ionic character  

 

Calculating Allen Factor

A.F.  =      D e.n. / S e.n. 

 

         -high Allen Factors predict ionic compounds  ( A.F. > 0.4)

         -low Allen Factors predict covalent molecules (A.F. < 0.4)  

 

          b. Modified Allen Factor equation- Using Allen Factor to calculate percent ionic character 

             Percent Ion character =  Allen Factor  x  1.3  x 100%  

 

    6. Writing & Naming Ionic Compounds-  

       a. Naming Cations

         1. Cations formed from metals have the same name as the metal

           -single atom ions with or without multiple oxidative states are called monatomic ions

         2. Cations that express multiple oxidation states (typically the transition metals) are named using

           a. -ic/-ous- archaic scheme used to differentiate between an elements ions with only 2 oxidation states  

           b. Roman Numeral Nomenclature- the Roman numeral is used that corresponds to the oxidation state

           c. Cations formed from nonmetal atoms have names that end in -ium

             Ions that are created from groups of covalently bonded atoms are called polyatomic ions

             - Here are some of the  Common Polyatomic Ions

 

 

Table:  Listing common Ion Names.  Print this out.

Assignment 2:   Naming Ionic Compounds worksheet .

     

      b. Naming Anions

        1. Monatomic anion name endings are changed to -ide.

           NOTE: There are some polyatomic anions that also end in -ide, so don't confuse them.

        2. Polyatomic anions containing oxygen atoms are called oxyanions and have name endings of -ite or -ate

           NOTE: -ate anions have 1 more oxygen atom than -ite anions

           -some groups of anions need prefixes to differentiate between anions. (Ex. chlorates & chlorites)

        3. Polyatomic anions that are made from adding an H+ to an oxyanion have the prefix hydrogen- or bi-

 

      c. Rules for Writing & Naming Ionic Compounds

        1. Cations are always written first  

        2. The sum of the oxidation numbers must equal zero- Electrically neutral species  

           i. Use subscripts in order to get the correct proportion of atoms.

           ii. The criss-cross method (oxidation #s to subscripts) works if you remember to reduce when necessary.

       3. Name the compound using correct naming scheme for the cation and anion

           Binary compounds- Composed of two different types of elements (metal/nonmetal)  

           Ternary compounds- Composed of more than two types of elements (compounds containing polyatomic ions)

           NOTE: A polyatomic anion name ending does not change

 

      c. Naming Acids

          Acid- A compound which donates H+ ions in an aqueous solution. The hydrogen functions as the cation in the

                   formula.

        1. binary acid- hydrogen is bonded to a single non-metal and dissolved in water.

          -To name these:

            a. use the prefix hydro-

            b. followed by the root of the non-metal

            c. end with the suffix -ic acid.

            

                Ex.      HCl(aq) -- hydrochloric acid,         HBr(aq) -- hydrobromic acid,          HF(aq) --  hydrofluoric acid, 

                          

                            HI(aq) --  hydroiodic acid,           H2Se(aq)  -- hydroselenic acid

 

         2. Ternary acids- hydrogen is bonded to a polyatomic acid and dissolved in water

            -To name these: 

                a. DO NOT use the hydro- prefix

                b. use the root of the polyatomic ion

                c. change -ate endings to -ic acid  or -ite ending to -ous acid

 

                Ex.      HNO3(aq) -- nitric acid                HNO2(aq) -- nitrous acid        HClO4(aq) -- perchloric acid

                       

                           HClO3(aq) --  chloric acid            HClO2(aq) -- chlorous acid    HClO(aq)   -- hypochlorous acid

 

Flowcharts: 

     Naming Cations,  Naming Anions,  Naming compounds w/ acids,  Naming Compounds. Good resources

 

Practice: Naming Ionic Compounds Games

 

assignment 3: Ch 15. Writing & naming ionic compounds worksheet

Review:  Chemical Bonding Quiz:

Assignment 4  : Ch. 15 Review Questions: p432; 23, 26, 28, 29, 32, 34, 37, 44, & 56

Special Links:

Rules of Thumb and Misconceptions for bonding