Lecture Notes:  Chemistry 111                                                        Week 2, Fall, 2004

Review:    Atomic Composition:

            Atomic Number = # Protons:  The number of protons/atom defines the atom and is called the atomic #.

            Electrons

            Neutrons

            Isotopes

 

Discovering the existence of isotopes:

            The Mass Spectrometer: In a mass spectrometer, charged particles are passed through a magnetic field.  The path of the stream of particles will be bent by the magnetic field depending on the mass and charge of the particles.  When naturally occurring samples of most elements  are charged and passed through a mass spectrometer, the spectrum indicates more than one form of the element.  These are isotopes of the element:  the number of protons is the same but the number of neutrons/atom differs for each isotope giving each isotope a slightly different mass.

           

 

                       

 

 

 

Isotopes=  Atoms with the same atomic number (# protons) and different numbers of neutrons.

 

Define symbolism to represent a particular atom of an isotope:

            A       charge                                         A= Mass number = (# protons +  # neutrons)

               X

            Z                                                             Z= atomic number

 

            Examples:

            Symbol                         64Cu                                         20Ne

            # protons                                 _29____                                    10

            # neutrons                               _35____                                    10

            # electrons                              _29____                                  _10___

            Charge of particle                  __0____                                      0

            Atomic number(Z)                  _29____                                  _10___

            Mass number(A)                    _64____                                  _20___

            Name of the element             copper                                   neon

 

The Modern Periodic Table:  Atoms are arranged by atomic number(the number of protons) which

is the identifying characteristic of an atom.

 

Elements:   What is the form of Naturally occurring elements?

a.       Some elements exist as DIATOMIC units in nature when not combined with other elements.  Learn the ones that exist as diatomic molecules in the elementary state:  I, Br, Cl, F, O, N, H

“I Bring Clay For Our New House” or the # 7 memory device(start with nitrogen, atomic

number 7)

b.      Most other elements are considered as MONATOMIC units in nature when not combined with other elements.

Examples:  Samples of He and Ne gases 

      Solid aluminum as Al atoms bound to each other in a metal solid

c.       Some exist as POLYATOMIC units

Sulfur can form S8 units, Carbon can form large units such as the “Bucky-Ball units, C60

           

Compounds:  Elements combine to form COMPOUNDS.   The different types of compounds: 

                        A.  Ionic compounds

                        B.  Molecular compounds

                        C.  Network Solids

 

A.  Ionic Compounds:  pages 57-62 in Chapter 2 of Chang

What are  “ions” and how are they formed? 

               Cations are positively charged particles formed when an atom loses one or more  electrons.

 

                                               

           

 

  Anions are negatively charged particles formed when an atom gains one or more electrons.

                                   

                                               

 

Ionic Compounds form when cations and anions attract each other:

            Ions attract each other to form a crystalline lattice of oppositely charged particles.

 

 

 

                                   

 

 

 

 

 

 

The crystalline material on the right is an ionic compound that is thought to be composed of oppositely charged ions which can be depicted as the structures on the left.  Notice that the ions are attracted to each other; each “red” anion is equally attracted to a number of “grey” cations and not to just  any specific cation.  The formula of an ionic compound gives the RATIO in which the ions are found in the compound.

Properties of Ionic Compounds

            High melting and boiling points, brittle, many are water-soluble

 

Solutions of ionic compounds with water:  The solid breaks apart into its cations and anions which move freely surrounded by water molecules.  A material that breaks down completely (~100%) into its ions in water is said to be a STRONG ELECTROLYTE.   In your Project 1 Lab you test the conductivity of water solutions of several ionic compounds.  Water solution of soluble ionic compounds conduct electricity

 

 

Recognizing Ionic Compounds (Are often called Salts):  Composed of metallic element that has reacted with a non-metallic element to from cations and anions which then attract  each other to form ionic  compounds.  In this example the metallic element sodium (Na) atoms give up electrons to become positive sodium ions (Na+) and non-metallic chlorine(Cl) atoms take electrons to become negative chloride ions (Cl-).  The oppositely charged ions then attract each other to form a crystalline lattice.

                                    *                                                          

Nature of Ionic compounds:  Know the physical properties of Ionic compounds:

                        High melting points, high boiling points, high Heats of Fusion/Melting (the heat needed to

melt a sample of material), high Heats of Vaporization/Evaporation (the heat needed to

evaporate a sample of material, many are water soluble (See p. 119).

                       

 

NOMENCLATURE:  Predicting simple binary ionic compound composition

1.      Check the name of the compound,

a.       An “ide” ending indicates (usually) a binary compound (a compound composed of only TWO elements.)  Example is sodium chloride which is composed of only sodium ions and chloride ions.

b.      An “ate” or “ite” ending for ionic compounds indicates that the compound involves one of the polyatomic ions containing oxygen.      

2.   Determine the formula and charge of the ions.

            3.   Write the formula using the general information and ratios.

            4.   Write the name:  Ion from the metal + Ion from the non-metal with “ide” ending

                        Cation     anion             compound                                name

                        Ba 2+         Cl 1-             ________                    ________________

Practice for Binary Ionic Compounds:

            Write the formula for:    MgCl2              Al2O3                    KI

 

Recognizing more complicated Ionic Compounds:  Check the ending    

            First-                Are you naming a Compound?

            Second-           Is it an Ionic Compound?

            Third-               Is it a Binary Ionic Compound? (Does the name end in“ide”?)

            Fourth-             If not, does the name end in  “ate” or “ite”?   If so, it is a more complicated ionic

compound and involves a Polyatomic ion

            ** Learn polyatomic ions (p60)

                        Example:   Write the formula for   sodium sulfate

 

Recognizing Hydrates:  Hydrates are solids in which water molecules have been caught in the crystal structure as the solid formed.  Formulas for hydrates indicate the water that is present in the ionic crystal in the following way.

                                                CaSO4 .5 H2O

 

 

 

 

B.  Molecular Compounds:  Composed of two or more non-metals that react to form an compound, a new material   

            Consider properties of Molecular Compounds: [Check Project 1 in lab]

                        Melting points?

                        Boiling points?

                        Heat of fusion(melting)? The heat needed to change solid--> liquid

                        Heat of vaporization(evaporation)? The heat needed  liquid--> gas

           

 

Formulas for  molecular compounds:  The name describes  the molecular unit.

Example of some simple molecules:

 

                                   

                                                                                    *

            Formulas for molecular compounds:

                        1.  Molecular compounds are composed of two or more non-metals.

2.  Binary molecular compounds. Names end in “ide”  :         Example:   carbon dioxide

Binary=  made of only two elements:  Example: 

                                                carbon dioxide  and  carbon monoxide

                        3.  Prefixes are used to relate the number of atoms in a molecule.                                                                                             Example:  carbon dioxide CO2 and       carbon monoxide         CO

             

                        Molecular formulas show the atoms that make the molecular unit.  An empirical formula

just shows the ratio of atoms in the molecular unit.        

 

            Molecular Formulas can be shown in several common forms:

Structural Formulas:

                       

            The Molecular Formula:  Shows the atoms that compose the molecular unit, the molecule

           

            The Structural Formula:  Shows how the atoms connect and the bonds that exist between atoms..

                                   

 

            3-D Formulas:

                        “Ball and stick” models

                                   

 

                        “Space-filling” models

                                   

           

In addition, for organic molecules, a “ Line Structure” model can be used.  The key to

understanding these formulas is:

1.      For atoms other than C or H, the symbol is shown in the line structure.

2.      At the end of each line and at the point where segments of line meet, there is a C atom.

3.      Each carbon must make four bonds.  When no other atom is indicated, H atoms are bonded.

                                           =    C5H8

 

Naming Acids:

            Our beginning definition of an acid will be a material that yields H+ ions when dissolved in water.  Therefore, we know that the first part of the acid will be the hydrogen with an oxidation number of +1.  The remainder of the acid will form one of the anions in water.  Let us divide the acids into TWO types”

Binary acids and Oxyacids.

            Binary Acids = two elements of which one is hydrogen.  The anion then must be a monatomic

anion and the ratio for the formula depends on the charge of the ions.

    For example:  HCl,   HBr,   H2S 

How do we name Binary Acids?

1.      The name of a binary acid begins with “hydro”.

2.      Name the anion and change the ending to “ic”:

Cl- = chloride ion  becomes  chloric

3.      Add the word “acid”.   Therefore, HCl is hydrochloric acid,

HBr is hydrobromic acid, H2S  is hydrosulfuric acid.

 

            Oxyacid = hydrogen and a polyatomic ion with oxygen.  For example:  H2SO4, H3PO4, HClO3

How do we name Oxycids?

1.      Name the anion and change the ending to “ic”, if the anion ends in “ate” or  to “our”, if the anion ends in “ite”, change the ending to “ous”.:

SO42- becomes “sulfuric”.;   SO32-  becomes “sulfurous”

2.   Add the word “acid”.  H2SO4= sulfuric acid,   H3PO4= phosphoric acid,

                                                HClO3 =” chloric acid

Nomenclature for Hydrates:

            Hydrates are compounds that have a specific number of water molecules trapped in the crystalline

lattice caught there as the material cooled slowly.

 

Name the compound using the appropriate rules above.  Express the nature of the

hydrate by adding  “bihydrate”,  pentahydrate, etc to the end of the name.

            Sr(NO3)2 . 4 H2O   =  strontium nitrate tetrahydrate

 

 

 

Types of energy:

            Kinetic energy

            Thermal energy

            Potential energy

            Chemical energy

            Electrical energy

 

Conservation of Energy:  Energy is neither created nor destroyed.  It may be transferred from one body to another or transformed from one form to another.

 

 

Preview for Week 3:

HOW MUCH MATERIAL IS IN A SAMPLE?  Quantitative Chemistry: The Mole

 

Mole = the number of particles in exactly 12.00 grams of isotope carbon-12

             which is 6.02 x 1023 atoms of carbon.

 

So our working definition of  MOLE is 6.02 x 1023 particles of a material

            Connecting the microscopic to the macroscopic:  THE MOLE

    How Many?

            1 mole = ____________________ (Avogadro’s number)

            1 mole carbon atoms= _____________atoms of C

            1 mole potassium atoms = ______________atoms of K

            1 mole hydrogen atoms = ____________ atoms of H

            1 mole of hydrogen molecules (H2)= _____________ H2 molecules

            1 mole of couples= _______________ couples and ______________ people.

            1 mole of water (H2O) molecules = ___________________ molecules(H2O)

                                                                  = ___________________ atoms of hydrogen

                                                                  = ___________________  atoms of oxygen

           

0.30 mole of carbon=  _______________carbon atoms

 

            Example :  Consider a sample of 4.5 moles of carbon dioxide?

a.       The formula of carbon dioxide is ___________

b.      The number of molecules in 4.5 moles of carbon dioxide is ___________

c.       The number of carbon atoms in 4.5 moles of carbon dioxide is ___________

d.      The number of oxygen atoms in 4.5 moles of carbon dioxide is _____________

e.       The total number of atoms in 4.5 moles of carbon dioxide is ________________

 

How Heavy?

Molar Mass = the mass of one mole of a material.  

The Molar Mass of each element is found under the symbol on the Periodic Table and represents the mass of one mole of the naturally occurring element.   It is determined by considering the mass and % of each isotope in a naturally occurring sample of the element.   Molar Mass of a Natural Sample of an Element (sometimes called Average Atomic Weight or Average Molar Mass) is determined as follows:

             

Average Molar Mass (element) = (fraction 1 x Molar Mass of Isotope #1) + (fraction 2 x Molar mass of

 Isotope #2 + ....  for each of the different isotopes)

     Example:  Molar Mass Average for Iron:

                        Iron has four isotopes:

                                    5.82 %  is iron-54   with mass of 53.940 g/mol

                                    91.66% is iron-56   with mass  of 55.935 g/mol

                                    2.19%   is iron-57   with mass of 56.935 g/mol

                                    .33%     is iron-58   with mass of 57.933 g/mol

Therefore:         Molar mass of naturally occurring iron(Fe) is

Molar Mass = (0.0582(53.940) + (0.9166)(55.935) + (0.0219)(56.935) + (0.0033)(57.933)

 

The Molar Mass of each element in a naturally occurring sample is found on the periodic table.

 

Molar mass = the mass of 1 mole of the material.

            Molar mass of:

                        1 mole hydrogen atoms = ___________________

                        1 mole calcium atoms = ____________

                        1 mole water

                                    2 moles hydrogen atoms ______

                                    1 mole oxygen atoms_______

                                    Therefore, Molar Mass of H2O= _______

                        1 mole hydrogen molecules, H2  _____________