Docstoc

Elements_ Atoms _ Intro to Atomic Structure

Document Sample
Elements_ Atoms _ Intro to Atomic Structure Powered By Docstoc
					1
   Over 112 known, of which 88 are found in
    nature
    ◦ others are man-made (synthetic)
   Each element has a unique symbol
   The symbol of an element may be one letter
    or two
    ◦ if two letters, the second is lower case
   Names come from various sources
    ◦ Latin, Greek or German word describing a
      property
    ◦ Person
    ◦ place

                                                 2
1. Elements are composed of atoms

2. All atoms of a given element are
identical

3. Atoms of a given element are different
from those of any other element



                                            3
4. Atoms of one element combine with
atoms of other elements to form
compounds.
    ◦ Law of Constant Composition
        all samples of a compound contain
         the same proportions (by mass) of
         the elements




                                             4
5. 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


                                           5
   a compound is a distinct substance that is
    composed of atoms of two or more
    elements

   The formula tells the types of atoms and
    the number of each type in the cmpd

   the number of atoms of each element is
    written to the right of the element as a
    subscript
    ◦ if there is only one atom, the 1 subscript
      is not written

                                                   6
   Each molecule of a compound that has
    been implicated in the formation of
    acid rain contains one atom of sulfur
    and three atoms of oxygen

   SO3




                                            7
 Eachmolecule of a certain
 compound contains two atoms of
 nitrogen and five atoms of oxygen

 N2O5




                                     8
 Eachmolecule of glucose, a type
 of sugar, contains six atoms of
 carbon, twelve atoms of hydrogen
 and six atoms of oxygen

 C6H12O6




                                    9
   J.J. Thomson investigated a beam
    called a cathode ray

   he determined that the ray was made
    of tiny negatively charged particles we
    call electrons

   his measurements led him to conclude
    that these electrons were smaller than
    a hydrogen atom

                                              10
   if electrons are smaller than atoms,
    they must be pieces of atoms

   if atoms have pieces, they must be
    breakable

   Thomson also found that atoms of
    different elements all produced these
    same electrons
 Tiny,   negatively charged particle

 Verylight compared to mass of
 atom
 ◦ 1/1836th the mass of a H atom

 Move very rapidly within the atom
 ◦ Located in the electron cloud
                                        12
   Discovered a positively charges mass
    (nucleus) in the atom

   Most 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
                                                 13
 The atom contains a tiny dense center
 called the nucleus

 The nucleus is essentially the entire mass
 of the atom

 Thenucleus is positively charged
  the amount of positive charge of the
  nucleus balances the negative charge of
  the electrons

 Theelectrons move around in the empty
 space of the atom surrounding the
 nucleus
                                               14
   The nucleus was found to be
    composed of two kinds of particles

   Some of these particles are called
    protons
    ◦ charge = +1
    ◦ mass is about the same as a hydrogen
      atom


                                             15
   Since protons and electrons have the
    same amount of charge, for the atom
    to be neutral there must be equal
    numbers of protons and electrons

   The other particle is called a neutron
    ◦ Discovered by James Chadwick
    ◦ has no charge
    ◦ has a mass slightly more than a
      proton
                            17




   We know atoms are composed of three
    main pieces - protons, neutrons and
    electrons

   The nucleus contains protons and
    neutrons

   The electrons move outside the
    nucleus (in the electron cloud)

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:54
posted:1/28/2013
language:simple
pages:17