Make your own free website on


Chemical Formulas and Bonding

I  Ionic Bonding
    A.  Ionic Bonds and Ionic Compounds
        1.  based on static electrical attraction
        2.  positively charged ions (metals, cations) attract negatively charged ions (nonmetals, anions)
        3.   forms ionic compounds
        4.  compounds electrically neutral ( - = +)
        5.  ions in an ionic compound have specific arrangement
        6.  properties
              a.  high melting point
              b.  brittle
              c.  dissolves in water
              d.  molten state or liquid state - good conductor of electricity
    B.  The octet rule
        1.  states that atoms tend to gain, lose, or share electrons in order to acquire a
             full set of valence electrons (8 electrons)
        2.  exception hydrogen and helium - 2 electrons
        3.  ionic bonds provides the element involved with a full set
        4.  octet represents a more stable configuration for the elements
    C.  Lewis dot diagrams
        1.  bonding involves valence electrons
        2.  represented by dots around the element's symbol
        3.  electrons are displayed alone or in pairs
        4.  used to demonstrate the changes that occur during chemical reactions
    D.  types of ions
        1.  monatomic cations
              a.  one atom
              b.  name same as the element
              c. transition elements - more than one ion add Roman numeral to name -   
                       Fe 2+   Iron (II)   
                       Fe 3+   Iron (III)
        2.  monatomic anions
              a.  mostly nonmetals
              b.  name uses suffix
              c.  oxygen becomes oxide
        3.  polyatomic ions
              a.  contains more than one atom
              b.  atoms covalently bonded
              c.  reacts as a single unit 
    E.  binary ionic compounds
        1.  simple combination of cation and anion
        2.  involves only two elements
        3.  compound name
              a.  first cation then the anion
              b.  lacks important information: ratio
        4.  ratio
              a.  included in an empirical formula 
              b.  represented by subscripts
              c. indicates the number of ions needed to produce a neutral compound 
1  Ca 2+  needs Cl 1-  to equal zero
                  1.  neutral compound
                  2.  empirical formula --> Ca1Cl2
                  3.  subscript 1 is assumed -->  CaCl2
        5.  works the same with polyatomic ion
              a.  requires parentheses if more than one polyatomic ion is needed
Mg 2+  needs 2  NO31-
              c.  Mg(NO3)2

II  Covalent Bonding
    A.  molecules and their formulas
        1.  formed by a shared pair of electrons between two atoms
        2.  compound called a molecule
        3.  consist of two atoms (O2) or millions (DNA)
        4.  properties vary widely
        5.  represented by a molecular formula
              a.  exact number of each atom in the molecule
              b.  also have empirical formula (simplest ratio)
              c.  C6H12O6 --> CH2O
        6.  structural formula
              a.  several compounds may have the molecular formula
              b.  differentiated by their structural formulas
                  1.  depicts which atoms are bonded to each other
                  2.  Lewis structures uses Lewis dot diagrams
                  3.  dots between atoms are shared
                  4.  O :: O
         7.  multiple bonds
              a.  single bond:  2 shared electrons   
                                       H : H  or  H - H
              b.  double bond:  4 shared electrons
                                       O :: O  or O=O
               c.  triple bond:  6 shared electrons
                                       N ::: N  or  N = N
    B.  exceptions
        1.  less than the octet  -- B only six electrons
        2.  more than the octet -- S or P
        3.  odd number of electrons -- N
    C.  properties of covalent bonds
1.  polar
              a.  unequal sharing of electrons
              b.  difference in the elements' electronegativity values
              c.  higher value element gains a higher electron density - partial negative charge
              d.  lower value gains a lower density - partial positive charge
2.  nonpolar
              a.  nearly equal sharing of electrons
              b.  similar or equal electronegativity values
        3.  nonpolar bonds - electronegativity values   <    .4
             polar bonds          -                                         .4 to 2.0
             ionic bonds           -                                         
>  2.0

III  Naming Chemical Compounds
    A.  naming ionic compounds
        1.  cations named first then the anion
        2.  if the cation can have more than one charge - a Roman numeral must be used   
              a.  remember:  net charge for the compound must be 0                                     
              b.  Cu(NO3)
              c. NO3  has a 1- charge, therefore (NO3)
2   = 2- 
              d.  Cu  must be 2+  to have net charge of 0
              e.  copper (II) nitrate
    B.  hydrates
        1.  ionic compounds that absorb water   CuSO4. 5 H2O
        2.  without water called anhydrous   CuSO4
        3.  properties are different
        4.  important to indicate the degree of hydration
        5.  Copper (II) sulfate pentahydrate
              a.  prefix used to indicate degree of hydration
              b.  penta - 5
    C.  naming molecular compounds
        1.  similar to ionic compounds
        2.  includes prefixes to indicate the number of atoms of each element
        3.  mono is not used for the first element - carbon dioxide
        4.  some are known by common names - water rather than dihydrogen monoxide
    D.  acids
        1.  substances that dissolves in water to produce H+ ions
        2.  name derived from the anion
        3.  if anion ends with ide
              a.  acid name begins with hydro
              b.  suffix changed from
ide to ic   
              c.  end with
              d.  HCl  -
hydrochloric acid
        4.  if anion does not end with ide
              a.  drop hydro
              b.  HNO3  - nitric acid