Chemistry 1364
General Chemistry I

Chapter 2 - Atoms, Molecules, and Ions

Atomic Theory of Matter

n     Democritus

n    Greek philosopher

n    First to propose finite divisions of matter

n    Was not the ‘common’ belief, so fell into disfavor

n     John Dalton

n    English schoolteacher

n    Proposed 4 postulates of atomic behavior which are the cornerstone for atomic theory

Dalton’s Postulates

n    Element - extremely small particles - atoms.

n    All atoms of an element are identical; atoms of different elements are different.

n    Atoms of one type are NOT changed into atoms of another type by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

n    Compounds - formed by combining atoms of more than 1 element, and always have the same number and type of atoms.

n    Elements - 1 type of atom.

n    Au, Na, Fe, etc...

n    Compound - 2 or more types of atoms combined chemically.

n    H2O, CO2, NaClO4, etc...

n    Mixture - no interaction of atoms in elements/compounds.

n    Sea water, coffee, iced tea, etc…

n     Law of conservation of mass

n    Mass the same at the end as the beginning.

n     Law of constant composition

n    Compound will always have the same ratio of elements

n     Law of multiple proportions

n    2 or more compounds from elements, then the masses of elements will be small whole number ratios.

n    Physics - Like charges repel each other; unlike charges attract.

n    Cathode rays

n    invisible, but can cause materials to fluoresce.

n    can 'bend' the rays w/magnetic or electric field.

n   Amount of bending can be used to determine the charge to mass (e/m) ratio.

n     Thompson

n     e/m = 1.76 x 108 coulomb / g

n    If charge or mass could be determined, the other could using the e/m ratio.

n     Millikan Oil Drop Experiment

n    Attempt to determine the charge on an electron.

n    Charge = 1.60 x 10-19 C

n    Mass = 9.10 x 10-28 g

n    (1.60 x 10-19 / 9.10 x 10-28) = 1.76 x 108

n     Radioactivity

n     X-rays

n    Not affected by magnetic fields

n    Form of energy

n    Becquerel - link to phosphorescence

n     Rutherford - 3 types

n    a - He nucleus (2+)

n    b - fast electrons (-)

n    g - similar to X-rays

n    Dalton – indivisible sphere

n    Thompson – Plum Pudding model

n    Banana nut muffin model

n    Nuclear atom

n    Rutherford/Geiger/Marsden experiment

n   scattering of a particles

n   some straight back!

n    later found protons and neutrons in the nucleus

Modern View

n     Electron charge = -1.602 x 10-19 couloumb

n     Proton charge = +1.602 x 10-19 couloumb

n    charges equal magnitude but opposite sign

n    refer relative as +1 or -1

n     Nucleus very small 

n    10-4 D vs atom at 1-5D

n    1 D = 10-10 m

n    Masses for atoms is extremely small

n    Largest atomic mass about 4 x 10-22 g!

n    Need an ‘atomic’ scale for masses

n    Atomic Mass Units

n     amu

n    Relative to the mass of a carbon atom

n    More later…..

n    Element defined by # of protons in the nucleus

n    # protons called the atomic number (Z)

n    isotopes - different # of neutrons

n    protons + neutrons = mass number (A)

n    indicate specific isotope by mass # and symbol - 12C, 16O, etc.

n    nuclide - atom of a specific isotope.

Problems 1, 3, 5, 11-17 odd

Periodic Table

n    Triads

n    early grouping of elements based on similar chemical and physical properties

n    Elements arranged

n    increasing atomic number

n    grouped w/similar properties in columns

n    Defines 'shape' of periodic table

n    More later….

n    Column - Family  or group.

n    IA - alkali metals

n    IIA - alkaline earth metals

n    VIA - chalcogens

n    VIIA - halogens

n    VIIIA - noble gases

n    North American labeling convention

Molecules and Ions

n    Molecules

n    Distinct packages of atoms bound together (covalent bonds)

n    can be same element or different elements (O2, HCl,C12H22O11,...)

n   Diatomic elements

n    must be neutral (no charge)

n    nonmetal/nonmetal

n     Formulas

n    molecular - what and how much

n    empirical - what in smallest whole number ratio

n    structural - what is hooked to what

n     Ions - charged particles

n    cations (+) and anions (-)

n    show charge by superscript following symbol (Na+, Al3+, S2-, Cl-, ...)

Types of Ions

n     monatomic - single atom gains/loses electrons

n    use periodic table to predict charge on monatomic ion.

n     polyatomic - groups of atoms (similar to molecules) w/charge.

n    Typically nonmetals with other metals

n    some polyatomic ions will consist of metals/nonmetals (CrO42-) of only metals (Hg22+)

Ionic compounds

n     held together by difference in charges

n     metal/nonmetal

n     no molecules - use empirical formulas.

n     Write formula by insuring the same number of + and - charges.

Problems 19, 21, 25, 29-37 odd


n     cations

n    element + ion  (Na+ - sodium ion) for A and Group 2B metallic ions (representative)

n    element + (charge in roman numerals) + ion for variable charge

n    Transition elements and heavier representatives

n    Fe2+ - iron(II) ion

n    Fe3+ - iron(III) ion

n     Table 2-4 lists the common cations

n    Learn BOTH formula and charge!

n     anions

n    drop end and replace with -ide

n    chlorine 6 chloride

n    sulfur 6 sulfide ...

n    polyatomic (oxy) anions

n    when two are formed, the one with more oxygens -ate; fewer -ite

n    NO3- - nitrate; NO2- - nitrite

n    more than 2 - use prefix per- (more, -ate) and hypo- (less, -ite)

n    look at the chlorine series

n    anions

n    polyatomic oxy anions with hydrogen

n   use hydrogen or bi-

n    CO32- - carbonate; HCO3- - hydrogen carbonate or bicarbonate

n    Table 2.5

n    Learn BOTH formula and charge!

n    Compound - name of cation with name of anion

n    NaCl - sodium chloride

n    CaCO3 - calcium carbonate

n    FeSO4 - iron (II) sulfate

n    Acids

n    binary - hydrostemic acid

n   HCl - hydrochloric acid

n   H2S - hydrosulfic acid

n    oxo-

n   -ate 6 -ic

n   -ite 6 ous

n   ClO4- - perchlorate; HClO4 - perchloric acid

n     Binary molecular compounds

n    use prefixes to indicate # of each type of atom

n    Table 2.6

n    last element ending changed to -ide

n    CO2 - carbon dioxide

n    N2O5 - dinitrogen, pentoxide

n     Common names

n    H2O - water; NH3 - ammonia

n    others…

Problems 39 - 49 odd