The Structure of Atoms

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					 The Structure of Atoms

     Thanks to those 7
scientists (and many more)
  what do we know about
       atoms today?!
             Structure of atoms

 Atoms can’t be broken into smaller pieces,
  BUT they are made of smaller pieces!
 Those smaller pieces all on their own don’t
  act like the element the atom is from.
 Atom: the smallest particle of an element
  with the chemical properties of that element.
             Two areas of an Atom

 Nucleus: made up of:
  Protons(+ positive), mass number = 1
  Neutrons (0 neutral), mass number = 1

  Make up the mass of the atom



                         +
                    0        0
                         +
 Electrons (- negative)
  Around   the nucleus
  Tiny, mass number = 0

  Lots of space between the nucleus and the
   electrons.

                      -
           Subatomic Particles

 Protons, neutrons and electrons
            Subatomic Particles

Subatomic   Charge         Location         Mass
Particle
proton      positive (+)   nucleus          1 amu
neutron     neutral (0)    nucleus          1 amu
electron    negative (-)   around nucleus   ~1/2000 amu
             Defining an Atom

 Nuclei (plural of nucleus) made of protons
  and neutrons
 Number of Protons (+) = number of
  electrons (-)
   Atoms are neutral!

 # protons tells us what kind of element an
  atom is!
           Holding it all together

 Nuclear forces hold protons and neutrons
  together
 The positive force of the nucleus holds the
  electrons near the nucleus.
   Positive and negative attract.
 Mass number = protons + neutrons
 Everything heavy in an atom
  Electrons   aren’t heavy at all!
         Atomic Number
      (= number of protons)   6
      Element Symbol
                              C
Element Name
                        Carbon
Average atomic mass     12.011
Protons   Neutrons Mass     Electrons Element
                   number
                -




        +
    0       0
        +




-
Protons   Neutrons Mass     Electrons Element
                   number

2         2       4         2        Helium
                -




            +
        +
            0
    0
        0
            +




-                   -
                                -

    -




                        +               -
        0
                +
                        0
            0               +
                0
                        +
            +
                    0




-                                   -
                -

                                        -

        -




                        +
                                +               -
                0                   +
                        +
-           0                   0
                    0               +
                            0
            0                   +
                    +
                            0




    -                                       -
                    -

                                                            -

        -

                                +
                                            0
                    0                               0
                                +
            +                               +                       -
                    0                               +
                                    +
-           0                               0
                        0                               +
                                    0
                0                               +
                            +
                                        0                               -
                                                +



    -                                                           -

                        -                                   -
                        -

                                                                -

            -

-                                   +
                0                               0
                        0                               0
                                    +
                +                               +                       -
                        0                               +
                                        +
    -               0                           0
                            0                               +
                                        0
                    0                               +
                                +
                                            0               +
                                                                            -
                                                    +



        -                                                           -

                            -                                   -
                    -

                                            -

        -



                    0
                            +
            +                       +               -
                    0                   +
                            +
-           0                       0
                        0               +
                                0
                0                   +
                        +
                                0




    -                                           -

                                        -
Protons   Neutrons Mass     Electron Element
                   number   s

2         2       4         2       Helium
3         3       6         3       Lithium
5         5       10        5       Boron
7         7       14        7       Nitrogen
10        10      20        10      Neon
11        11      22        11      Sodium
8         8       16        8       Oxygen
            Which element…?

 Has 20 protons?
            Which element…?

 Has 15 protons?
            Which element…?

 Has 17 protons?
            Which element…?

 Has 53 protons?
            Which element…?

 Has 79 protons?
            Which element…?

 Has 40 electrons?
             Which element…?

 Has 77 electrons?
            Which element…?

 Has 50 electrons?
             Which element…?

 Has 118 electrons?
         Atomic Number
      (= number of protons)   6
      Element Symbol
                              C
Element Name
                        Carbon
Average atomic mass     12.011
         Protons: defining an atom


 Atomic number: Atoms of different elements
 have different numbers of protons.
         Trends in Atomic Numbers

 Atomic numbers increase to the right and
  down the Periodic Table of the Elements.
 Check it out.
Isotopes
            Average atomic mass
            -                                   -




 6                          +
                                    +                   -



C
                    0                       +
                            +
                                    0
                        0
                                            0
                                0
                                    +
                        +
12.01                           0




        -                                           -
                                        -
 But why is the atomic mass (on the periodic
 table) different from the mass number
 (protons + neutrons)?
  Carbon atomic mass = 12.011 amu

  Mass number = 12 amu
                        Isotopes

 Atoms of the same element can have different numbers
    of neutrons.
   Because these atoms have the same number of
    protons, they are the same element, and acts the same
   More or fewer neutrons only changes the mass of the
    atom!
   Isotopes are atoms of the same element with different
    masses because of different numbers of neutrons
   Identified by mass number
             Naming Isotopes

 Mass number (A): the total number of
  protons and neutrons in the nucleus of an
  isotope
 Hyphen Notation:
   Element-Mass number

   Hydrogen-3
 Nuclear Symbol

    mass _ number
  atomic _ number   Symbol
  A
  Z   X
               Nuclear symbols

 Helium-4: 4 is the mass number
  The  total number of protons plus neutrons
 This helium isotope can also be written:
   4He
   2

 4   is the mass number, 2 is the number of
    protons
 Write the nuclear symbol for Carbon-13
   13C
   6
               Nuclear symbols

 Helium-4: 4 is the mass number
  The  total number of protons plus
   neutrons
 This helium isotope can also be written:
      4
      2   He
 4  is the mass number, 2 is the number of
   protons (from the periodic table)
         Isotope Notation

       Mass
                27
      number

      Atomic
      number
                13   Al
• Al-27
• Aluminum-27
                -




        +
    0       0
        +




-
            -




0       0
    +
            -




        +
    0
        +




-
                                -

    -




                        +               -
        0
                +
                        0
            0               +
                0
                        +
            +
                    0




-                                   -
                            -

    -




                    +               -
        0
                +
                    0
            0           +
                0
                    +
            +




-                               -
                -

                                        -

        -




                        +
                                +               -
                0                   +
                        +
-           0                   0
                    0               +
                            0
            0                   +
                    +
                            0




    -                                       -
                -

                                        -

        -




                        +
                                +               -
                0                   +
                        +
-           0                   0
                    0               +
                            0
            0                   +
                    +




    -                                       -
        -                               -




                            +
-                                   +           -
                    0
                            +
            +                       0
                        0
                                0
                0                   +
                        +
                                0




    -                                       -
                                -

    -




                        +               -
        0
                +
                        0
            0               +
                0
                        +
            +
                    0




-                                   -
                            -

    -




                    +               -
        0
                +
                    0
            0           +
                0
                    +
            +




-                               -
                -

                                        -

        -




                        +
                                +               -
                0                   +
                        +
-           0                   0
                    0               +
                            0
            0                   +
                    +
                            0




    -                                       -
                -

                                        -

        -




                        +
                                +               -
                0                   +
                        +
-           0                   0
                    0               +
                            0
            0                   +
                    +




    -                                       -
           Practice naming Isotopes
 The notation Sn-117 represents an isotope of
  the element ____________.
 Its mass number is ________.
 Since its atomic number is __________,
  the atom contains
   _________ protons,

   _________ electrons and

   _________ neutrons.
 Cesium-133 is an isotope whose mass
  number is _________.
 Its atomic number is ________.
 The atom contains _______ protons,
 ________ electrons and
 ________ neutrons.
 An isotope contains 27 protons and 39
  neutrons. The isotope is an atom of the
  element ____________.
 Its atomic number is _________.
 This atom has _______ electrons.
 Its mass number is __________.
         Applications of Isotopes

 Over time (a long time!) one isotope can lose
 neutrons and turn into another.
Measure the % of C-14 to calculate age
 What objects have been dated using carbon-
 14 isotopes?
Shroud of Turin
The Giant Periodic Table Project

              6

           C
         Carbon
         12.011
     The Giant Periodic Table Project

 Be neat
 Be bold! We need to be able to read this
  from anywhere in the room!
 Be creative, but not cluttered.
 Be accurate.
 Atomic mass to TWO digits (Ex: 12.01) is
  ideal.
           Calculating your grade



 Let’s imagine that      Your averages for
 your grade in biology    each of the
 was based on the         categories are:
 following:
                           Tests: 79%
  40% Tests
  30% Labs
                           Labs: 88%

  20% Homework            Homework: 65%
  10% Class work          Class work: 90%
                 Now you try:



 Let’s imagine that      Your averages for
 your grade in biology    each of the
 was based on the         categories are:
 following:
                           Tests: 90%
  40% Tests
  30% Labs
                           Labs: 70%

  20% Homework            Homework: 85%
  10% Class work          Class work: 95%
           Mixtures of Isotopes

 In nature, elements occur as a mixture of
  isotopes.
 We use the weighted average of the isotope
  masses – average atomic mass
 On the periodic table, the average atomic
  mass is below the element name.
 Check it out.
             Example: Chlorine

 In nature, chlorine exists as:
  75.77%chlorine-35
  24.23% chlorine-37

(35  75.77)  (37  24.23)
          100
            35.453
 In nature, the element lithium has isotopes
  in the following natural abundance:
   7.5% lithium-6

   92.5% lithium-7

 Calculate the average atomic mass.
                           Mass spectrum of copper
relative number of



                     100
                      80        69.09
       atoms




                      60
                      40                              30.91
                      20
                       0
                                  63                   65
                                        mass number
 Copper has two naturally occurring isotopes.
 They are present in the following percents:
          63
  69.09% Cu
         29
                         63
                          Cu


           65
  30.91    Cu
           29
 

  Calculate    the average atomic mass.
Calculate the average atomic mass of Ne

                              Mass spectrum of neon
   relative number of



                        100      91
                         80
          atoms




                         60
                         40
                         20                           9
                                            0.3
                          0
                                 20          21       22
                                        mass number
 So what if someone gives us the mass of a
  sample of an element?
 How do we figure out how many atoms we
  have?
 We use…
 THE MOLE
                  The mole

 Mole: The SI unit for amount of substance
 Contains as many particles as there are
  atoms in 12 grams of carbon-12
 There are 6.022x1023 atoms in 12 grams of
  carbon-12
 Avogadro’s Number = 6.023x1023
                Molar Mass

 The mole: the amount of a substance that
  contains one Avogadro’s number (that is,
  6.022x1023) of particles.
 Molar mass is the mass of one mole of a
  pure substance (units: g/mol)
           Find the molar mass of…

 Oxygen
        Find the molar mass of…

 Phosphorus
           Find the molar mass of…

 Sodium
         Find the molar mass of…

 Gold

				
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