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CHEMICAL FOUNDATIONS_ ELEMENTS AND ATOMS

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					CHEMICAL FOUNDATIONS:
 ELEMENTS, ATOMS AND
        IONS


 Chapter 4
  ANCIENT GREEKS’ VIEW
       OF MATTER
About 400 B.C. , Aristotle thought all matter
  was made of four “elements” :
• earth
• air
• fire
• water
  ANCIENT GREEKS’ VIEW
       OF MATTER
At about the same time another Greek
 philosopher, Democritus, said that matter
 was made of tiny, indivisible particles called
 atoms.
Atomos is the Greek word for indivisible.
 The Early History of Chemistry
- Before 16th Century
  Alchemy: Attempts (scientific or otherwise) to
  change cheap metals into gold--mercury, sulfur,
  & antimony were discovered.
- 17th Century
  Robert Boyle: First “chemist” to perform
  quantitative experiments. Father of modern
  chemistry--gave the modern definition to an
  element.
       The Early History of
      Chemistry (continued)
- 18th Century
 George Stahl: Phlogiston flows out of a burning
 material.
 Joseph Priestley: Discovers oxygen gas,
 “dephlogisticated air.”
Law of Conservation of Mass

 - Discovered by Antoine Lavoisier

 - Mass is neither created nor destroyed

 - Combustion involves oxygen, not
   phlogiston
 Other Fundamental Chemical Laws

Law of Definite Proportion (Law of
Constant Composition)

- A given compound always contains exactly
  the same proportion of elements by mass.

- Carbon tetrachloride is always 1 atom
  carbon per 4 atoms chlorine.
 Figure 4.1: John
Dalton (1766-1844)
  Dalton’s Atomic Theory (1808)

1 Each element is made up of tiny particles
  called atoms.
2 The atoms of a given element are identical;
  the atoms of different elements are
  different in some fundamental way or
  ways.
      Dalton’s Atomic Theory
                (continued)

3 Chemical compounds are formed when
  atoms combine with each other. A given
  compound always has the same relative
  numbers and types of atoms.
4 Chemical reactions involve reorganization
  of the atoms - changes in the way they are
  bound together. The atoms themselves are
  not changed in a chemical reaction.
         Dalton’s Atomic Theory
Atoms are indivisible in a chemical process.
   all atoms present at beginning are present at
    the end
   atoms are not created or destroyed, just
    rearranged
   atoms of one element cannot change into
    atoms of another element
     cannot turn Lead into Gold by a chemical
       reaction
     CHEMICAL ELEMENT
• a substance that cannot be further
  decomposed into simpler substances by
  chemical or physical means.
• consists of atoms that all have the same
  atomic number.
• approximately 115 elements are known.
• 88 elements occur naturally.
• microscopic--single atom of an element.
• macroscopic--enough atoms to weigh on a
  balance.
Table 4.1: Distribution (Mass Percent) of the
 18 Most Abundant Elements in the Earth's
      Crust, Oceans, and Atmosphere
    CHEMICAL ELEMENTS
        (continued)
What two elements make up nearly 75 % of
  the solid earth?
oxygen--49.2 % & silicon--25.7%

What element is found in atmosphere, crust,
  and oceans of the earth?
oxygen
Table 4.2: Abundance of elements in the
              human body
       Jons Jakob Berzelius
• developed the system of using letters to
  stand for elements instead of symbols like a
  crescent moon for Silver.
• 1st letter of symbol must be capitalized.
• 2nd letter (if there is one) is never
  capitalized.
• Symbols are often from Greek, Latin, or
  German.
Table 4.3: The names and symbols of the
         most common elements
        Chemical Symbols
Symbols commonly missed.
• A -- Al, Ar, As, Au, & Ag.
• B -- Ba, Bi, B, Br, & Be.
• C -- C, Ca, Cd, Cl, Cr, Co, Cs, & Cu.
• M -- Mg, Mn, & Mo.
• S -- S, Sb, Si, Sr, & Sn.
• Latin -- Fe, Au, Ag, Sb, Pb, Na, K, Hg, &
  Cu.
• German -- W
      Chemical Compound
• can be broken down into simpler substances
  by chemical means.
• has a definite composition.
• energy changes accompany the formation of
  a compound.
• Examples: CO, CO2,, NO, N2O, NO2, N2O3,
  N2O5, SO2, SO3, As2S3, & As2S5.
Figure 4.16: (a) Sodium chloride (table salt) can
 be decomposed to the elements sodium metal
              and chlorine gas (b)
   The Chemists’ Shorthand:
          Formulas
Chemical Formula:
  Symbols = types of atoms
  Subscripts = relative numbers of atoms
                     CO2
Structural Formula:
   Individual bonds are shown by lines.
                  O=C=O
       Chemical Formulas
How many atoms of each element are found in
the following compounds?

• Ba(NO3)2

• (NH4)2SO4

• Ca(C2H3O2)2

• Ca3(PO4)2
       Early Experiments to
      Characterize the Atom
- J. J. Thomson - postulated the existence of
  electrons using cathode ray tubes.
- William Thomson (Lord Kelvin) - proposed
  the “plum pudding” model of the atom.
- Ernest Rutherford - explained the nuclear
  atom, containing a dense nucleus with
  electrons traveling around the nucleus at a
  large distance.
Figure 4.7: Schematic of a cathode ray
                tube
      02_21




                          Applied
                          electric field   (+)




(-)



              Metal                                          (+)
              electrode
                                           (-)
                                                 Metal
                                                 electrode




Cathode ray tube like the one used by J. J. Thomson to
determine the charge and relative mass of the electron.
Figure 4.8: A CRT being used to display
           computer graphics
  Thomson’s Plum Pudding Model
Electrons suspended in a positively charged electric
   field
    must have positive charge to balance negative
      charge of electrons and make the atom neutral
mass of atom due to electrons
atom mostly “empty” space
    compared size of electron to size of atom
Figure 4.3: The
 plum pudding
    model
   02_23




                            Oil spray

Atomizer to
produce oil
                                                   X rays produce
droplets
                                                   charges on the
                                                   oil drops
                                        (+)

Microscope



           Electrically
           charged plates
                                        (-)




           Oil drop apparatus used by Milliken to determine
           the mass of the electron.
  Figure 4.4: Ernest
Rutherford (1871-1937)
Figure 4.5: Rutherford’s experiment on -
   particle bombardment of metal foil
            Rutherford’s Results
Over 98% of the  particles went straight through
About 2% of the  particles went through but were
 deflected by large angles
About 0.01% of the  particles bounced off the gold
 foil
Figure 4.6: (a) The results that the metal foil
 experiment would have yielded if the plum
pudding model had been correct; (b) Actual
                   results
  Rutherford’s Nuclear Model
The atom contains a tiny dense center called
  the nucleus
   the volume is about 1/10 trillionth the
     volume of the atom
The nucleus is essentially the entire mass of
  the atom
The nucleus is positively charged
   the amount of positive charge of the
     nucleus balances the negative charge of
     the electrons
The electrons move around in the empty space
  of the atom surrounding the nucleus
           The Modern Atom
The nucleus contains protons and neutrons
The nucleus is only about 10-13 cm in diameter
The electrons move outside the nucleus with an
 average distance of about 10-8 cm
  therefore the radius of the atom is about 105
    times larger than the radius of the nucleus
 Figure 4.9: A
 nuclear atom
viewed in cross
    section
    The Modern View of Atomic
           Structure
The atom contains:
- electrons: found in the electron shells, they have
  a negative charge. (J.J. Thomson)
- protons: found in the nucleus, they have a
  positive charge equal in magnitude to the
  electron’s negative charge.
- neutrons: found in the nucleus, virtually same
  mass as a proton but no charge. (James
  Chadwick)
The Mass and Charge of the
Electron, Proton, and Neutron

Particle   Mass (kg)         Charge
                       31
Electron   9.11  10           1

Proton     1.67  1027       1+
                       27
Neutron    1.67  10           0
           Subatomic Particles
Particle     Location   Mass #   Relative
                                 Mass
Proton       Nucleus       1      1836

Neutron      Nucleus       1      1839

Electron     Electron      0       1
             Shells
                   Isotopes
• Their discovery changed Dalton’s Atomic Theory
  to say: “All atoms of the same element contain the
  same number of protons and electrons, but atoms
  of a given element may have different numbers of
  neutrons.”
• Atomic number (Z) -- number of protons in the
  nucleus
• Mass number (A) -- sum of the number of protons
  and neutrons in the nucleus.
                    Isotopes

All isotopes of an element are chemically identical
   undergo the exact same chemical reactions
Isotopes of an element have different masses
Isotopes are identified by their mass numbers
   mass number = protons + neutrons
Figure 4.10: Two isotopes of sodium
       The Chemists’ Shorthand:
           Atomic Symbols

 Mass number 39
Atomic number 
               19 K    Element Symbol



   Isotopes are “top heavy” -- mass
   number is larger and on top.
 Determining # of Subatomic
          Particles

             A=Z+N
How many protons, neutrons, and electrons
are found in the three isotopes of carbon,
carbon-12, carbon-13, and carbon-14?

   6 protons, 6 electrons, and 6, 7, or 8 neutrons
             Periodic Table
Elements classified by:
   - properties
   - atomic number

Groups (vertical)
  1A = alkali metals
  2A = alkaline earth metals
  7A = halogens
  8A = noble gases

Periods (horizontal)
          The Modern Periodic Table
Main Group = Representative Elements
   “A”    columns
Transition Elements
   all   metals
Bottom rows = Inner Transition Elements = Rare
 Earth Elements
   metals
   really   belong in Period 6 & 7
 Important Groups - Halogens
                            Bromine = Br2
Group 7A = Halogens             brown liquid that
very reactive nonmetals          has lots of brown
react with metals to form        vapor over it
ionic compounds                 Only other liquid
                                 element at room
Fluorine = F2                    conditions is the
    pale yellow gas             metal Hg
Chlorine = Cl2              Iodine = I2
    pale green gas             lustrous, purple
                                 solid
    Important Groups
Noble Metals (Coinage Metals)
Ag, Au, Pt
all solids at room temperature
least reactive metals
found in nature uncombined with
other atoms
               Noble Gases
• appear in nature in the uncombined state.
• all colorless gases at room temperature
• very non-reactive, practically inert eight electrons
  in outer shell (octet) except helium which has two
  (duet).
• monatomic gases (single atom molecules)
• six noble gases are:
  He                       Kr
  Ne                       Xe
  Ar                       Rn
 Figure 4.13:
  Argon gas
 consists of a
 collection of
separate argon
    atoms
Figure 4.14: Gaseous nitrogen and oxygen
  contain diatomic (two-atom) molecules
 Diatomic Elemental Molecules
Elements that exist as diatomic (two atom) molecules

  Remember: Count HOFBrINCl
        H2
        O2
        F2
        Br2
        I2
        N2
        Cl2
                02_29                                                                                                    Noble
                     Alkaline                                                                                            gases
                   1 earth metals                                                                            Halogens     18
                  1A                                                                                                      8A

                   1                                                                                                       2
                   H    2                                                                    13   14   15    16    17     He
                        2A                                                                   3A   4A   5A    6A    7A

                   3    4                                                                    5    6    7     8     9      10
                  Li    Be                                                                   B    C    N     O     F      Ne

                   11   12    3        4    5     6        7     8    9     10    11    12   13   14   15    16    17     18
                  Na    Mg                              Transition metals                    Al   Si   P     S     Cl     Ar
Alkali metals




                   19   20   21        22   23    24      25    26    27    28    29    30   31   32   33    34    35     36
                   K    Ca   Sc        Ti   V     Cr      Mn    Fe    Co    Ni    Cu    Zn   Ga   Ge   As    Se    Br     Kr

                   37   38   39        40   41    42      43    44    45    46    47    48   49   50   51    52    53     54
                  Rb    Sr   Y      Zr      Nb    Mo      Tc    Ru    Rh    Pd    Ag    Cd   In   Sn   Sb    Te    I      Xe

                   55   56   57        72   73    74      75    76    77    78    79    80   81   82   83    84    85     86
                  Cs    Ba   La*    Hf      Ta    W       Re    Os    Ir    Pt    Au    Hg   Tl   Pb   Bi    Po    At     Rn

                   87   88   89     104     105   106     107   108   109   110   111
                  Fr    Ra   Ac†    Unq Unp Unh Uns Uno Une Uun Uuu


                                            58    59      60    61    62    63    64    65   66   67   68    69    70     71
                         *Lanthanides       Ce    Pr      Nd    Pm    Sm    Eu    Gd    Tb   Dy   Ho   Er    Tm    Yb     Lu

                         † Actinides        90    91      92    93    94    95    96    97   98   99   100   101   102    103
                                            Th    Pa      U     Np    Pu    Am    Cm    Bk   Cf   Es   Fm    Md    No     Lr




                             Periodic Table of the Elements
  The Modern Periodic Table
Elements with similar chemical and physical
  properties are in the same column
Columns are called Groups or Families
Rows are called Periods
Each period shows the pattern of properties
  repeated in the next period
Why does the periodic table have 7 periods?


 There are 7 electron shells.

Why does the periodic table have 8 groups?

 Eight electrons is the maximum for an
 outer electron shell.
Stair step or zig-zag line separating metals
from nonmetals.
              Allotropes
• different forms of the same element
• the different physical properties arise from
  the different arrangements of the atoms in
  the solid
• the three allotropes of carbon are:
  diamond               buckminsterfullerene
  graphite
Figure 4.18a: The three solid elemental
      (allotropes) forms of carbon
Figure 4.18b: The three
     solid elemental
  (allotropes) forms of
          carbon
    Figure 4.18c: The three solid elemental
          (allotropes) forms of carbon




(c) Buckminsterfullerene
 Physical Properties of Metals
Metals are:
1. efficient conductors of heat and electricity.
2. malleable (Can be hammered into thin
  sheets).
3. ductile (Can be pulled into wires).
4. lustrous (shiny).
Examples are: Na, Cu, Au, Ag, & Fe.
      Physical Properties of
           Nonmetals
Nonmetals are:
1. nonconductors of heat and electricity
  (insulators).
2. not malleable, but are brittle.
3. not ductile.
4. dull and without a luster.
Examples are: H, He, N, O, S, & P.
              Metalloids
• substances with the properties of both
  metals and nonmetals.
• also called semimetals
• Lie along the zigzag line between metals
  and nonmetals
• The six metalloids are:
  B, Si, Ge, As, Sb, and Te.
    Electrical Nature of Matter


Most common pure substances are very poor
 conductors of electricity
  with the exception of metals and graphite
  Water is a very poor electrical conductor
      Electrical Nature of Matter
Some substances dissolve in water to form a
  solution that conducts well - these are called
  electrolytes.

When dissolved in water, electrolyte compounds
 break up into component ions.
       Solution Conductivity
In order for a substance to conduct electricity,
  it must:
• contain ions.
• ions must be free to move (mobile).

Ions become mobile when the substance is:
• dissolved in water.
• melted (fused).
Figure 4.20: (a) Pure water does not conduct a
 current; (b) Water containing a dissolved salt
               conducts electricity
                   Ions
Ion: an atom or group of atoms with a net
  positive or negative charge.
Ions are never formed by changing the
  number of protons!

Cation: A positive ion
                 Mg2+, NH4+

Anion: A negative ion
                Cl, SO42
       The Chemists’ Shorthand:
           Atomic Symbols

 Mass number 39    1+  Ion charge

Atomic number 
               19 K  Element Symbol
       Atomic Structures of Ions

Metals form cations
For each positive charge the ion has 1 less
 electron than the neutral atom
  Na = 11 e-, Na+ = 10 e-
  Ca = 20 e-, Ca+2 = 18 e-
                   A=Z+N
              z    # protons # electrons # neutrons
35        0
17   Cl
              17      17         17          18

35    1-
17   Cl       17      17         18          18
Figure 4.12: The elements classified as
         metals and nonmetals
 NONMETALS

NONMETAL + n e- ------> Xn-
      where n = 8 - Group #
C + 4 e- ---> C4- C4- carbide
N + 3 e- ---> N3- N3- nitride
O + 2 e- ---> O2- O2- oxide
F + e- ---> F1- F- fluoride
      METALS
M ---> Mn+ + n e-
where n = periodic group
Na ---> Na+ + e-
Mg ---> Mg2+ + 2 e-
Al ---> Al3+ + 3 e-
Transition metals --> M2+ or M3+
                        are common
       Atomic Structures of Ions
Cations are named the same as the metal
     sodium     Na  Na+ + 1e-        sodium ion
     calcium Ca  Ca+2 + 2e-          calcium ion
The charge on a cation can be determined from the
 Group number on the Periodic Table for Groups
 IA, IIA, IIIA
   Group   1A  +1, Group 2A  +2, (Al, Ga, In)  +3
PREDICTING ION CHARGES


 In general
 metals (Mg) lose electrons ---> cations
 nonmetals (F) gain electrons ---> anions
Charges on Common Ions
                -4 -3 -2 -1
+1

 +2            +3
          Chemical Bonds
- the forces that hold two or more atoms
   together to form a compound.
- the two types of chemical bonds are:
       1. Ionic bonds.      metal & nonmetal
            NaCl KI
       2. Covalent bonds. two nonmetals
            H2O CH4
          Chemical Bonds
            (continued)
Ionic Bonding: Force of attraction
  between oppositely charged ions.
- Chemical compounds must have a net
  charge of zero.
  1. Both cations and anions must be present.
  2. The number of cations and anions must
     be such that the net charge is zero.
Writing Formulas for Ionic
       Compounds
                  Charge must
                  equal zero for
                  each compound.
   1        1-
Na Cl             1+ & 1- = 0
   2   1
Ca F    2
                  2+ & 2- = 0
  3    2-
Al S
  2     3
                  6+ & 6- = 0
COMPOUNDS FORMED
    FROM IONS
          CATION + ANION --->
          COMPOUND


          Na+ + Cl- --> NaCl

          A neutral compound
           requires equal
           number of (+)
               and (-) charges.
Figure 4.21a: The
  arrangement of
sodium ions (Na+)
 and chloride ions
  (Cl-) in the ionic
compound sodium
      chloride.
IONIC COMPOUNDS
ammonium chloride,
NH4Cl
NH4+


  Cl-
Some Ionic Compounds
        calcium fluoride

Ca2+ + 2 F- ---> CaF2
Name = calcium fluoride
Mg2+ + 2 NO3- ----> Mg(NO3)2
magnesium nitrate
3Fe2+ + 2PO43- ----> Fe3(PO4)2
iron(II) phosphate or ferrous
  phosphate

				
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