Chapter Two:

Atoms, Molecules & Ions

• Atomic Theory & Structure
• Isotopes, Numbers & Masses
• Periodic Table
• Molecules, Ions, Compounds & Formulas
• Naming Species

Atomic Theory and Structure

• What is the smallest piece of matter possible?
• Democritus called the smallest particles "atomos"
• Dalton's atomic
• elements are composed of small particles -- atoms
• all atoms of an element are identical
• atoms are not created or destroyed chemically
• compounds formed by chemical combination of two
  or more elements
• a given compound has same relative number &
  type of atoms (law of constant composition)
• atoms retain character during chemical rxns. only
  undergo rearrangement (conservation of matter)
• Law of Multiple Proportions
  If two elements, A & B, form more than one compound, the masses of B that can combine with a given mass of A are in a ratio of small whole numbers

Subatomic Particles

-J.J. Thompson determined charge:mass ratio of e-, 1897
-Robert Millikan measured charge of e-, 1909
-Thompson developed "plum pudding" model of atom
-Rutherford developed "nuclear" model of atom

• Atomic Number
• number of protons in an atom
• defines an element
• shown as the symbol subscript 6C
• Mass Number
• total number of protons plus neutrons
• will vary between isotopes
• shown as the symbol superscript 12C
• Isotopes
• elements which have the same atomic number
  but different mass numbers

¹²C6 ¹³C6 ¹⁴C6 are isotopes

• Periodic Table
• Allow for organization of elements
• Allows for grouping of elements in terms of
  physical and chemical characteristics
• Metals, Non-metals & Metalloids
• Group 1A Alkali Metals
• Group 2A Alkaline Earth Metals
• Group 6A Chalcogens
• Group 7A Halogens
• Group 8A Nobel Gases
• B Groups Transition Metals
  

Know these !!

• Molecules and Molecular Compounds
• Molecule
• the smallest particle of a compound that can be
  identified as that compound
• chemical combination of two or more atoms
• a pure substance
• Chemical Formula
• a symbol representation of a molecule/compound
• shows the type and ratio of atoms in a molecule
• type is given by symbol ratio is given by a subscript to right of symbol
  

Examples:

Molecule Ratio

H2O       2 : 1     heteroatomic

H2O2      2 : 2     heteroatomic

CO2             1 : 2           heteroatomic

CO        1 : 1     heteroatomic

O2             -        homoatomic

• Formulas
• Molecular Formulas
  Give the type and exact number of each type of atom
  

-Empirical Formulas
Give only the type and simplist ratio of atoms

Molecular Formula       Empirical Formula

H2O                                  H2O

H2O2                                 HO

C6H6                                 CH

C2H6                                 CH₃

Structural Formulas
Show which atoms are attached to which atoms

Ions & Ionic Compounds

• Some elements will either lose or gain one or more
  electrons to become charged species
• Metals

typically lose electrons, become +, cations

• Non-Metals

typically gain electrons, become -, anions

• Monatomic Ions
• made from a single element

Na ® Na⁺ + 1e^-

Cl + 1e^- ® Cl^-

Hints to Determine Ion Charges

• Hydrogen         +1
• Oxygen            - 2
• Group IA         +1
• Group IIA        +2
• Group VIA      - 2
• Group VIIA     - 1

• Polyatomic Ions -- "molecules" which have a net
  positive or negative charge
• CO3^2-   carbonate ion
• NH4⁺ ammonium ion
• OH^- hydroxide ion

• Prediction of Charges -- all species tend toward the
  most stable state
• Nobel gases are very stable

Elements add or lose electrons to "mimic" nobel gases

Ionic Compounds

• Oppositely charged ions form ionic compounds
• held together by ionic bonds due to the electrostatic attraction between the opposite charges
• Ionic compounds are always neutral species

Mg²⁺ and Cl^- form MgCl2 not MgCl or Mg2Cl

Naming Inorganic Compounds

• Names of Monatomic Ions

cations are named for the elements
Na⁺ is sodium ion Al⁺³ is aluminum ion
Fe⁺² is iron(II) ion Fe⁺³ is iron(III) ion
(ferrous ion) (ferric ion)
Cu⁺ is copper(I) ion Cu²⁺ is copper(II) ion
(cuprous ion) (cupric ion)

anions are named for the root name of the element with the ending -ide
O^-2 is oxide ion Cl^- is chloride ion
H^- is hydride ion N^-3 nitride ion

Naming Polyatomic Ions

• Know the names, charges and formulas of the important polyatomic ions
• NH4⁺ ammonium ion
• CO3^-2 carbonate ion
• SO4^-2 sulfate ion
• OH^- hydroxide ion
• NO3^- nitrate ion
• Polyatomic ions are treated as separate entities or units

Naming and formula rules are the same as for compounds with monatomic ions

Naming Binary Ionic Compounds

• Cations always named first
• Anions always named last
• NaCl sodium chloride
• BaCl2 barium chloride
• for cations which have more than one possible charge, the charge of the ion must be given in the name
• Fe2O3 iron(III) oxide
• FeO iron(II) oxide

Combinations must be neutral!

• Examples:
  
• 2 Na⁺ and 1 CO3^-2 is sodium carbonate
  Na2CO3
• 2 NH4⁺ and 1 S^-2 is ammonium sulfide
  (NH4)2S
• 1 Ba⁺² and 2 OH^- is barium hydroxide
  Ba(OH)2
• 3 Mg⁺² and 2 PO4^-3 is magnesium phosphate
  Mg3(PO4)2
• 1 Na⁺ , 1 H⁺ and 1 CO3^-2 is sodium hydrogen carbonate or sodium bicarbonate, NaHCO3

Acids

• A compound that produces hydrogen ions (H⁺) when dissolved in water
• tastes sour
• turns litmus red
• has a pH less than 7
• typically the formula begins with one or more H's
• HCl(aq) hydrochloric acid
• H2SO4(aq) sulfuric acid
• HC2H3O2(aq) acetic acid

Binary Acids

• Acids which contain H and another non-metallic element
• Naming -- to the root name of the non-metallic element:
• add the prefix hydro-
• add suffix -ic acid
• HF(aq) hydrofluoroic acid
• HBr(aq) hydrobromic acid
• HCl(aq) hydrochloric acid

Oxyacids

• Acids which contain H and O and another element (or H and a polyatomic anion containing O)
• Naming -- to the polyatomic ion name
• if the suffix is -ate, change it to -ic
• if the suffix is -ite, change it to -ous
• add acid to the end of the name
• HNO3 nitric acid HNO2 nitrous acid
• H2SO4 sufuric acid H2SO3 sulfurous acid

You must know polyatomic ion
names/charges

Binary Molecular Compounds

• Chemical combinations of non-metals and non-metals (no ions involved)
• The more metallic element is named first
• The second element (less metallic) is named with the ending -ide
• Because there are no ions to use to determine relative ratio of atoms we must indicate the number of each atom by a prefix
• N2O3 dinitrogen trioxide
• SO3 sulfur trioxide

Name the Following

• CaI2 calcium iodide
  
• Cu2O copper(I) oxide
  
• CuO copper(II) oxide
  
• Cl2O7 dichlorine heptoxide
  
• HClO3 chloric acid

Write Formulas for the Following:

• calcium hypochlorite Ca(ClO)₂
  
• Mg⁺² and ClO2^- Mg(ClO₂)₂
  
• carbon tetrachloride CCl₄
  
• NH4⁺ and SO₄^2- (NH₄)₂SO₄