Atomic Structure by kASYpW

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									        4.2
THE STRUCTURE OF AN
       ATOM
Atomic Structure
• Atoms are composed of 2 regions:
 • Nucleus: center of atom that contains mass
   of atom
 • Electron cloud: region that surrounds
   nucleus that contains most of space in atom

                                    Nucleus
             Electron
             Cloud
What’s in the Nucleus?
• Nucleus contains 2 of 3 subatomic
particles:
 • Protons: subatomic particle w/ 1+ charge (p+)
   • Rutherford - 1911
 • Neutrons: subatomic particle w/ no charge
  (no)
  • James Chadwick - 1932
What’s in the Electron Cloud?
• The 3rd subatomic particle resides
outside nucleus in electron cloud
 • Electron: subatomic particle w/ 1- charge
  (e-) and virtually no mass
    • JJ Thomson - 1897
How do these particles interact?
• Protons and neutrons live compacted in tiny
 nucleus
  • most atom’s mass
• electrons small and reside outside nucleus
  • small mass (2000 e- = 1 p+ or no)
  • occupy large volume of space outside nucleus




     Atoms
How do the subatomic particles balance
each other?
• In atoms:
 • protons = electrons
   • If 20 protons are present in atom then 20
     electrons balance overall charge of atom—atoms
     are neutral
 • The neutrons have no charge; therefore they
  do not need to (and often times don’t) equal
  protons or electrons
How do we know the number of
subatomic particles in an atom?
 • Atomic #: indicates # of protons in
  atom
  • Ex: Hydrogen’s atomic # is 1
    • hydrogen has 1 proton
  • Ex: Carbon’s atomic # is 6
    • carbon has 6 protons
 **Number of protons identifies element
      similar to how your fingerprint ID’s you.
   Ex. 2 protons = He, 29 protons = Cu
                   ALWAYS!!
How do we know the number of
subatomic particles in an atom?
• Mass number: number of protons and
neutrons in nucleus (p+ + no)
 • Ex: hydrogen can have a mass # of 3.
  Since it has 1 proton it must have 2 neutrons

 • # of neutrons = mass # - atomic #
What are Isotopes?
• Atoms of same element with different #
of neutrons
• Same atomic #
• Different mass # (b/c neutrons are
  different)
    • Ex. Carbon 12, Carbon 13, and Carbon 14 all
      naturally occurring isotopes of Carbon.
    • Each has 6 p+ and 6 e-, but each has
      different # of neutrons (therefore,
      different mass#)
Determining the number of protons and
neutrons
 • Li has mass # of 7 and atomic # of 3
   • Protons = 3 (same as atomic #)
   • Neutrons= 7-3 = 4 (mass # - atomic #)


 • Ne has a mass # of 20 and an atomic # of 10
   • Protons = 10
   • Neutrons = 20 - 10= 10
What about the electrons?
• electrons are equal to protons
 • So e- = p+ = atomic #
• Ex: He has mass # of 4 and atomic # of 2
 • p+ = 2
 • no = 2
 • e- = 2




Basic Atomic Structure 1:57
Determine the number of subatomic
particles in the following:
• Chlorine has a mass # of 35 and an
atomic # of 17
 • p+ = 17, no = 18,   e- = 17

• Potassium has a mass # of 39 and an
atomic # of 19
 • P+ = 19,       no = 20        e- = 19
Candy Atoms
• Atom #1 - mass # of 5 and an atomic # of 3.


• Atom #2 – 5 protons and 7 neutrons.


• Atom #3 – Atomic # of 7 and 8 neutrons.
Candy Atoms
• Atom #4 – mass # 18 and 9 electrons


• Atom #5 – build your own candy atom using the candies
 that you have. You should be able to accurately
 determine:
 • Atomic #
 • Mass #
 • # of protons, neutrons, and electrons
4.3 Modern Atomic
     Theory
Bohr Model of the Atom
• Agreed with Rutherford
 • Small nucleus w/ lots of
  space


• Devised planetary model
 • trying to show why e-
   were not sucked into p+ in
   nucleus of atom.
 • e- in specific energy levels
Misconceptions from the Bohr Model
• Bohr model good for diagramming atoms
 and energy levels
• e-   do NOT move like planets in
  predictable orbits
• Mathematics determine probable
  location of e-
Energy Levels
• Possible energies e- can have
• Like floors in hotel
 • Floor nearest nucleus - ground floor
The Electron Hotel
• Levels nearer nucleus have lower energy
 (ground floor of hotel)

• Electrons fill energy levels from inside -
 outside. (ground floor - top floor of
 Electron Hotel)
Electron distribution in an Atom   Energy
                                   Level
                          3d        3
                 3p
           3s
  ENERGY




                 2p                 2
           2s



                                     1
           1s
                NUCLEUS
Energy Levels
• Can’t stand “in between”
  steps in hotel stairwell
• e-’s can’t exist “in
  between” energy levels
 • Must absorb energy to
   move up energy levels
 • Must lose to move down
Evidence of Energy Levels
• Energy gains & loses can be measured
• As e- drop orbitals, energy released in
 form of light/heat
 • Like in fireworks (2:34)
  Electron Cloud Model
• Electrons travel around
  nucleus in random orbits.
• cannot predict location at any
  given moment.
• fast, appear to form “cloud”
  around nucleus.
 • Ex. - Airplane propeller
Atomic Orbitals
• Rooms in “Electron Hotel”
  • Region of space where e- likely located
  • Each orbital can have 2 e- max
• Denser region = higher probability

             Energy Levels, Orbitals, and Electrons


         Energy        Number of     Maximum number of
           Level        Orbitals          electrons
        (floors in   (hotel rooms)      (occupants)
          hotel)
            1             1                   2

            2             4                   8

            3             9                   18

            4             16                  32
Electron Configuration
• Arrangement of e-’s (occupants) in orbitals
  (rooms)
• Each orbitals holds 2 e-’s max (1 double
  bed)
 • Stable when e-’s in orbitals w/ least energy
    • Ground state
    • i.e. Lithium (atomic # = 3) has 1st 2 e-’s in the
      1st energy level (fills up 1 room w/ double bed)
    • 3rd e- goes to 2nd energy level
Electron Configuration
• If Lithium absorbs
enough energy, 3rd e-
jumps energy levels
 • Excited state
 • Less stable (like gymnast
   on beam)
 • Eventually releases
   energy (often as light)
 • Returns to ground state
How exactly are the particles
arranged?
• Bohr Model of the atom:
Electrons move in orbits at fixed distances from the nucleus (planetary
  model)
                                                        All of the
                                                        protons and
                                                        the neutrons
      The 3rd ring
      can hold up
      to 18 e-                                           The 1st ring can
         The 4th ring                                    hold up to 2 e-
         and any after                               The 2nd ring can
         can hold up to                              hold up to 8 e-
         32 e-
What does carbon look like?
   Mass # = 12            atomic # = 6


                                  6 p and 6 n live
                                  in the nucleus




   p+ = 6        no = 6         e- = 6
Drawing Atoms
• Draw the following atoms in your notes:
• 1. Beryllium has an atomic # of 4 and a mass # of 9
Beryllium Atom
Drawing Atoms
• 2. Sodium has an atomic # of 11 and a mass # of 23
Sodium Atom

								
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