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"To the dull mind all nature is leaden. To the illumined mind the whole world burns and sparkles with light." -- Ralph Waldo Emerson

 

ATOMIC STRUCTURE AND THE PERIODIC TABLE

On this page:

Concept Pages:

Physical Science "Key
                       Concepts" Home Page


Section Review Questions
Chapter Review Questions
 

Chemical Symbols
 
  • An abbreviation for the name of an element:  C, O, He, Ag, Pb, etc.
  • 1, 2 or 3  letters:
  • If 1 – uppercase.
  • If 2 or 3 - first uppercase, second lowercase.
  • Some are derived from Latin.
    iron = ferrum
Matter and Atoms
• The Greeks reasoned that there was a smallest particle of nature, the "atom."

• They were right, (the atom is the smallest part of an element that has the properties of that element)

• but now that which we call an atom is known to be made of even smaller particles.
Parts of Atoms

Protons....

Neutron....

   + Positive electromagnetic charge.

  n Neutral - no electromagnetic charge.
 

These two particles make up:

The    Nucleus....

    +  Positive electromagnetic charge.
It is surrounded by:

    Electrons....

   -   Negative electromagnetic charge.
   

• Mass is 1/1800 that of proton.

 

The NEUTRAL atom (NO electromagnetic charge - n ) is..................

  

  a balanced atom 

  # protons = # electrons

Atomic Number

• Number of protons in the nucleus define the element.
If the number of protons is changed, then it is a different element.

Let me say that again: the number of protons is the thing that identifies the element!

Models of the Atom
Commonly pictured as :      The Planetary Model.   
 
  • Developed by Danish Physicist Niels Bohr in 1913.
  • Electrons look like planets orbiting a sun, (the nucleus),

    but with their orbits in spherical paths all around the nucleus, not in a plane.
Current Model :
• The Electron Cloud model.
• Developed by 1926.
• Electrons move so fast, they resemble a cloud.
• Electrons look like a sphere with the nucleus, not really visible, at the center.

Refinement of the Electron Cloud Model

• Primarily not spherical.

• Electrons found to be in "probable" locations.
Heisenberg Uncertainty Principle:

Electrons' location and velocity cannot be determined at the same time.

 
Energy Levels and Electrons  - "Atomic Orbitals," "Electron Configuration"

Links:

Orbital Central

Wikipedia
ChemicalElements.com
  • Electrons occupy different energy levels, or "shells."
  • Some of these shells are spherical.
  • Some of the shells are axial.
  • Shells closer to the nucleus are less energetic than those further away.
  • Shells hold specific maximum numbers of electrons:
    •
     
    A simplified table:
    Energy Level Max # Electrons

    1

    2

    2

    8

    3

    8

    4

    8

     
    Atomic Mass

    • The approximate mass of a proton or a neutron:

    =   1 atomic mass unit - 1 amu - (1 u in text).
    • Based on carbon 12,
        with 6 protons,
          6 neutrons,
                and the negligible mass of its 6 electrons.
    Mass Number
    • Sum of # of protons and # of neutrons.
    Isotopes
    • The number of neutrons is sometimes different from the norm for that element.

     
    An Isotope of an element:
    • IS that element, because of the # of protons,
    But
    • Has a different number of neutrons than most atoms of that element.
    Such as:

    C12 - 6 protons, 6 neutrons

    C14 - 6 protons, 8 neutrons
    And:

    B10 - 5 protons, 5 neutrons

    B11 - 5 protons, 6 neutrons

    Average Atomic Mass
    What is usually meant when we say

    Atomic Mass.

    Average of all the isotopes of a particular element.

    So, for instance:

     
    Carbon is 12.01

    • Because of the existence of some C14,
       but mostly of C12

    Boron is 10.81
     

    •  Because of the existence of some B10,
       but mostly of B11

    The Periodic Table of the Elements

    From the Los Alamos National Laboratory  (Copyright)
    Periodic Table
    Links:

     

    Los Alamos National Laboratory:


    		   Wikipedia  POPSCI.com

    ChemicalElements has a menu of links on the left side that will explain certain things like 'Groups' - Chemical Elements.com - Online Periodic Table of the Elements

     

    ---We could simply LIST the elements---

     
    • But in science we like to organize things to make them MUCH easier to find, to understand, to use...
    In the Late 1800s:
    • Dimitri Mendeleev
    • Russian chemist.

    Upon arranging elements:
    1. According to mass,

      2. He discovered patterns,

        3. Or periodicities.
     

    This became a "periodic table"

      for example,

    •   The calendar is a "periodic table of days":
          the periods are the weeks, (    containng all the days)
          the groups are the days (    e.g., column 1 is all Sundays)
     

    Has since been refined to the modern version:
    Based on:

        - Atomic number

        - Properties (Physical and Chemical)

    Groups, or Families:

    Alkali Metals             IA (1) Other Metals (14)
    Alkali Earth Metals   IIA (2) Nonmetals (15)
    Transition Metals  IIIB - IIB (3-12) Halogens       VIIA 
    Rare Earth Metals (13) Noble Gases   VIIIA (O, 18)
    Link:
    ChemicalElements.com (click on the group names in the menu on the left)    		  

    • The vertical columns are each a group.

    • Numbered 1 - 18 from left to right.

    • Members of a group share many properties, or traits.

    • Mostly because members of a group tend to have the same number of electrons in their outer shell.
    For Example:
    • Group 17 (or VIIA - halogens),

    with 7 electrons in their outer shell,
    tend to form compounds with group1,
    which have only 1 electron in their outer shell.
    • Group 18, (noble, or inert, gases),

    with 8 electrons in their outer shell, tends to form no compounds with any group.

    (The exception to electron #:  Helium, with 2 e-, but its 1 shell is full!)
     Periods
    • The horizontal rows are each a period.
    • Numbered 1 - 7, top to bottom.
    • Members of a period have the same number of electron energy levels.
     

    For Example:
    • Na and Cl have 3 electron energy levels,
        though Na has only 1 electron there,
        and Cl has 7 electrons there.
    Other Traits of Elements
    Metals • Shiny
    • Good conductors
    •  Solids at room temperature                    
    Nonmetals •  Gases or brittle solids at room temp
                          •  Poor conductors
    Metaloids •  Have some properties of both Metals and Nonmetals

     
    Transition Elements •  Groups 3 - 12 AND

    •  Periods 4, 5, and 6

    •  Have primarily metal properties

     
    Identifying New Elements
    • Heavier elements that may have existed in the distant past (according to current theory, a fraction of a second after the "Big Bang") or
    • have been produced in countless Supernova explosions throughout the rest of the history of the Universe.

     
    •  but can now only be discovered by combining 2 or more smaller elements.

    • This can only be done in a device called a particle accelerator, which "shoots" particles like atoms at each other at extraordinary speeds.

    • At these high energies, previously unknown heavy elements may be formed.

    • Most of these elements exist in the accelerator for only nanoseconds, then break down into smaller elements again. (they may exist naturally in a supernova explosion - you don't want to be there to see it!)

    Updated 11/02/2007