Atoms_ Elements_ Compounds_ and Mixtures by pptfiles

VIEWS: 7 PAGES: 9

									Atoms, Elements,
Compounds, and
    Mixtures
             Structure of the Atom
 Atoms are the smallest particles    All atoms share the same basic
  into which matter can be divided     structure. Over the years,
  and still maintain its               scientists have designed many
  characteristics.                     different models for this structure.
 Atoms are the building blocks of    Each one was the best model at
  the universe. There are 92           the time, but as new evidence was
  different kinds of atoms that        discovered, the models were
  occur naturally.                     revised.
 These building blocks can be        Scientists will probably revise the
  joined together to create all of     current model as more evidence
  the different kinds of matter we     becomes available.
  can observe.



                                 ?
 What’s inside of an
 atom?
                 Early Atomic Models
                                                                       “Atoms are
 The Greek scientist Democritus was                                   indivisible.”
the first person to say that all matter is                             - Democritus
made of atoms, but he also said that
atoms are indivisible.
                 Atoms of an
                 element are alike.    In the early 1800’s, the English scientist John
                                      Dalton developed his Atomic Theory of Matter.
                                      It said four things: (1) All matter is made of
        Different elements            atoms. (2) Atoms of an element are alike. (3)
        have different
        atoms.                        Atoms of different elements are different. (4)
                                      Atoms of different elements join together to
    +          =                      make compounds.                          Positively-
                                                                                 charged matrix
Atoms join to make compounds.     - John
Dalton
                                                                                  Negatively-
In the late 1800’s, J. J. Thomson                                                charged
                                                                                  electron
discovered that atoms were made of
smaller particles. He discovered the                                              - J. J.
                                                                                  Thomson
electron and devised the “chocolate-chip
cookie” model of the atom.
                  Recent Atomic Models                         Protons are in the
                                                               nucleus.
   In the early 1900’s, scientists                                 - Rutherford
  discovered the positively-charged proton.
  In 1911, Rutherford discovered the
  nucleus of the atom, where protons are
  located. Atoms are mostly empty space.

                                  Niels Bohr changed Rutherford’s model in
Electrons orbit
the nucleus.                     1913. Bohr said that electrons move around
 - Niels Bohr                    the nucleus in fixed energy levels. Electrons
                                 can move from one energy level to another.
                                 Bohr’s model has been called the “solar
                                 system” model of the atom.
                                                              Negative electron cloud
    The current model of atomic
   structure is called the “electron cloud”                    Neutral neutrons are
   model. Electrons move within an                             in nucleus with
                                                               positive protons.
   energy level in an ever-changing path,
                                                                - electron cloud
   not a fixed orbit. Neutrons bond with                       model
   protons in the nucleus.
           Atomic Number and Mass
                   Number
 All atoms of an element have the  Atoms of the same element may
  same number of protons, and         have different numbers of
  different elements have different   neutrons. Atoms with extra or
  numbers of protons in their         missing neutrons are called
  atoms.                              isotopes.
 The atomic number of an atom is  An atom’s mass number is the
  the number of protons it has. If    number of protons plus neutrons.
  the atom is neutral, the atomic    Different isotopes of an element
  number is also the number of        have different mass numbers.
  electrons.                                        Mass number of this
 Atomic number of                                  neutral atom is 14. This is
 this neutral atom =                               the sum of the protons plus
 6. This means                                     neutrons. Since there are
 that it has 6 protons                             6 protons, there must be 14
 and 6 electrons.                                  - 6 = 8 neutrons.
                                                   (protons are blue, electrons
                                                   are yellow, and neutrons
                                                   are green)
                             Elements
 An element is matter that is         At room temperature, most
  made of only one kind of atom.        elements are solids, although a
  All of the atoms of an element        few are liquids and some are
  are alike. There are 92               gases.
  naturally occurring elements.        Chemical symbols are
 Elements can be identified by         abbreviations for the names of
  their properties. Some                elements. You can also use a
  properties are color, texture,        chemical symbol to represent one
  density, malleability, ductility,     atom of an element. Chemical
  ability to dissolve in water, and     symbols are the same all over the
  ability to conduct heat or            world, no matter what language is
  electricity.                          spoken.


                             Na
                                                Chemical symbol for the
   Chemical symbol for the                      element Chlorine, used
   element Sodium, used in                      in bleach and water
   sodium vapor lamps.                          treatment.



                             Cl
                              Compounds
 The atoms of most elements are            Compounds are separated into two
  very reactive. They chemically             groups, depending on how their
  join together with atoms of other          atoms are joined: (1) Molecular
  elements to form compounds.                compounds are made of atoms that
 The properties of compounds are            share electrons. (2) Ionic compounds
  different than the properties of           are made of atoms that gain or lose
  the elements that make the                 electrons.
  compound.                                 Chemical formulas represent
 When elements join to make                 compounds. They show the kind
  compounds, they always join in             and number of atoms in the
                                                                         H is symbol for
  the same proportion. H2O is
  water, not HO or H3O ! O is symbol for
                                             compound.
                                               N is symbol
                                               for Nitrogen
                                                                NH3      Hydrogen


   H is symbol
   for Hydrogen
                     H2O      Oxygen

                              No subscript
                                               No subscript
                                               means one                  Subscript 3
                                               Nitrogen                   means there are
Subscript 2                   means one                                   3 Hydrogen
                                               atoms
means that there              Oxygen atom                                 atoms
are 2 Hydrogen
atoms

                    Water                                     Ammonia
                   molecule                                   Molecule
                             Mixtures
 Mixtures are made when there
  are at least two different kinds of
  atoms that are in the same
                                                       This coffee is a
  place but are not chemically                         mixture.
  combined.
 A mixture can be made with any
  proportion of ingredients, but a
  compound must be made in
  only one certain way.                 This cake is
                                        a mixture.
 Components of a mixture keep
  their own properties, but those
  of a compound do not.
 Components of a mixture are
  not chemically combined, so
  they can be separated by                                 This basket of fruit
                                                           is also a mixture.
  physical means like filtering or
  evaporation.
                       Types of Mixtures
 A homogeneous mixture is the
  same throughout. All parts of the
  mixture have the same proportion
  of ingredients.                                               This cookie is
 A heterogeneous mixture is                                    heterogeneous.

  different in different parts.
  Different regions of this kind of
  mixture have different proportions         Soft drinks are
  of the ingredients.                        homogeneous
                                             mixtures.
 An alloy is a homogeneous mixture
  of metals.                        The crayons in the         The alloy these keys are
                                        pail make a            made of is a homogeneous
                                        heterogeneous          mixture.
                                        mixture.


                                                                           The milk is
                                                                           homogeneous.
   The gelatin mold is a
   heterogeneous
   mixture.

								
To top