Atomic structure by YcZNzQ2v

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									S.MORRIS 2006
Where did it all begin?
   The word “atom”
    comes from the
 Greek word “atomos”
     which means
      indivisible.
   The idea that all
 matter is made up of
    atoms was first
   proposed by the
  Greek philosopher
 Democritus in the 5th
     century B.C.
         HISTORY OF THE ATOM

460 BC   Democritus develops the idea of atoms



              he pounded up materials in his pestle and

              mortar until he had reduced them to smaller

              and smaller particles which he called



                      ATOMA
                  (greek for indivisible)
       HISTORY OF THE ATOM

1803   John Dalton



            suggested that all matter was made up of

            tiny spheres that were able to bounce around

            with perfect elasticity and called them



                     ATOMS
   Dalton’s Atomic Theory (1808)
1. Elements are composed of extremely small particles
   called atoms.
2. All atoms of a given element are identical.
  The atoms of one element are different from those of
any other element

3. Atoms of different elements can combine in simple
   whole number ratios to form compounds.

 4. Chemical reactions only involve the rearrangement of
    atoms. Atoms are not created or destroyed in chemical
    reactions.
                                                         2.1
16 X   +   8Y   8 X2Y


                        2.1
   Law of Definite Proportions
• The ratio of mass of elements in a
  compound is always the same

• Every Water molecule will contain 16g of
  oxygen and 2 g of hydrogen
2




    2.1
       HISTORY OF THE ATOM

1898   Joseph John Thompson



           found that atoms could sometimes eject a far

           smaller negative particle which he called an




                 ELECTRON
         HISTORY OF THE ATOM
1890
Thompson develops the idea that an atom was made up of

electrons scattered unevenly within an elastic sphere surrounded

by a soup of positive charge to balance the electron's charge

                             like plums surrounded by pudding.



                                 PLUM PUDDING
                                       MODEL
        HISTORY OF THE ATOM

1910             Ernest Rutherford
 1910



           oversaw Geiger and Marsden carrying out his
           famous experiment.

           they fired Helium nuclei at a piece of gold foil
           which was only a few atoms thick.

           they found that although most of them passed
           through. About 1 in 10,000 hit
           (1908 Nobel Prize in Chemistry)




                                  particle velocity ~ 1.4 x 107 m/s
                                 (~5% speed of light)

1. atoms positive charge is concentrated in the nucleus
2. proton (p) has opposite (+) charge of electron
3. mass of p is 1840 x mass of e- (1.67 x 10-24 g)
                                                               2.2
                        Rutherford’s Model of
                        the Atom




    atomic radius ~ 100 pm = 1 x 10-10 m
nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m




                                             2.2
         HISTORY OF THE ATOM

                                                 gold foil
                      helium nuclei




                                                helium nuclei


They found that while most of the helium nuclei passed
through the foil, a small number were deflected and, to their
surprise, some helium nuclei bounced straight back.
         HISTORY OF THE ATOM


Rutherford’s new evidence allowed him to propose a more
detailed model with a central nucleus.


He suggested that the positive charge was all in a central
nucleus. With this holding the electrons in place by electrical
attraction



However, this was not the end of the story.
       HISTORY OF THE ATOM

1913   Niels Bohr


              studied under Rutherford at the Victoria
              University in Manchester.

              Bohr refined Rutherford's idea by adding
              that the electrons were in orbits. Rather
              like planets orbiting the sun. With each
              orbit only able to contain a set number of
              electrons.
Chadwick’s Experiment (1932)
               H atoms - 1 p; He atoms - 2 p
               mass He/mass H should = 2
               measured mass He/mass H = 4



         + 9Be         1n   + 12C + energy
neutron (n) is neutral (charge = 0)
n mass ~ p mass = 1.67 x 10-24 g
                                               2.2
         Subatomic Particles

                Mass         Charge      Charge
  Particle
                 (g)       (Coulombs)    (units)

Electron (e-) 9.1 x 10-28 -1.6 x 10-19    -1

Proton (p)   1.67 x 10-24 +1.6 x 10-19    +1

Neutron (n) 1.67 x 10-24       0           0


       mass p = mass n = 1840 x mass e-
                                                   2.2
Bohr’s Atom

                        electrons in orbits




              nucleus
                     Atoms
• # of protons &
  neutrons
• The basic unit of
  Matter
• The smallest particle
  of an element that
  retains the properties
  of that element.
            HELIUM ATOM
                                             Shell
proton




                      +
                          N
                                      -
                          +
           -          N




electron                                  neutron

What do these particles consist of?
    ATOMIC STRUCTURE
       All About Atoms

Particle    Charge       Mass

Proton     + charge      1amu

Neutron    No charge     1 amu

electron   - charge      1/1836
     ATOMIC STRUCTURE


            2

He
                Atomic number
                 Represents the number of
                 protons in an atom
                 Never changes
                 P+ equal to the number of e-

            4    Mass Number
                  the number of protons and
                  neutrons in an atom
                  Neutrons equal
                  mass # - atomic #

number of electrons = number of protons
Ions
Charged particles due to the loss or gain of electrons

2) Atoms that are called cations lose e- thus
becoming positive


                  11 protons                      11 protons
        Na        11 electrons            Na+     10 electrons


1) Atoms that are called anions gain e- thus become
negative


                  17 protons                      17 protons
         Cl       17 electrons            Cl-     18 electrons
                                                                 2.5
               Isotopes
• Atoms with the same atomic number but
  different mass number
• Atoms having the same number of protons
  but different numbers of neutrons

• Average Atomic Mass of an element is the
  weighted average of an element’s
  naturally occurring isotopes
2.3
       Do You Understand Isotopes?
              Isotope Maker

How many protons, neutrons, and electrons are in 14
                                                  6   C?
     6 protons, 8 (14 - 6) neutrons, 6 electrons


How many protons, neutrons, and electrons are in 11
                                                  6   C?
     6 protons, 5 (11 - 6) neutrons, 6 electrons


                                                       2.3
Atomic number (Z) = number of protons in nucleus
 Mass number (A) = number of protons + number of neutrons
                   = atomic number (Z) + number of neutrons
# OF NEUTRONS = mass number – atomic number


             Mass Number      A
                              ZX
                                       Element Symbol
            Atomic Number


                1           2            3
                1H          1H   (D)     1H   (T)
                    235            238
                     92   U         92   U

                                                          2.3
     Bohr Model of the Atom
• Electrons travel around the nucleus in one
  of several orbits/shells/ nrg levels
• Principal energy level is designated by a
  quantum number (n)
• Quantum number is the same as period on
  the periodic table
                     2.4




      Noble Gas
         Halogen
          Group
           Period
Alkali Earth Metal
     Alkali Metal
          ATOMIC STRUCTURE

 Electrons are arranged in Energy Levels or

 Shells around the nucleus of an atom.


• first shell            maximum of 2 electrons

• second shell           maximum of 8 electrons


• third shell             max of 18 electrons


• fourth shell             max of 32 electrons
           ATOMIC STRUCTURE

There are two ways to represent the atomic

structure of an element or compound;


           1. Electronic Configuration



          2. Electron dot diagrams
     ELECTRONIC CONFIGURATION

With electronic configuration elements are represented

numerically by the number of electrons in their shells

and number of shells. For example;


 Nitrogen            configuration = 2 , 5




                                             N
  2 in 1st shell                        14

  5 in 2nd shell
                                        7
          2   +    5 = 7
          ELECTRONIC CONFIGURATION

Write the electronic configuration for the following
elements;

     20            11                    8
a)        Ca      b)    Na          c) 16O
     40                23


  2,8,8,2               2,8,1                 2,6

                   14
d)
     17
      Cl          e)        Si      f)
                                         5
                                             B
     35                28                11

     2,8,7                  2,8,4             2,3
                Valence
• Valence shell is outermost occupied
  energy level and is the same as the period
  number in the periodic table

• Valence electrons are the electrons in the
  outer energy level of an atom
        DOT & CROSS DIAGRAMS

With Dot & Cross diagrams elements and compounds

are represented by Dots or Crosses to show electrons,

and circles to show the shells. For example;
                              X




                                               N
Nitrogen             X X      N     X X            7



                                                   14
                              XX
        DOT & CROSS DIAGRAMS

Draw the Dot & Cross diagrams for the following
elements;
           8                17
                                       X
    a) O            b)  Cl 35 X                X
          16                           X
        X                        X           X
              X
            X              X X X Cl X X            X
  X         O   X
                                 X           X
            X                          X         X
      X       X                X
                                      X
                     SUMMARY
1. The Atomic Number of an atom = number of
     protons in the nucleus.

2. The Atomic Mass of an atom = number of
     Protons + Neutrons in the nucleus.

3.   The number of Protons = Number of Electrons.

4.   Electrons orbit the nucleus in shells.


5.   Each shell can only carry a set number of electrons.

								
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