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Elements make up the periodic table.

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Elements make up the periodic table. Section 1.2D Elements can be organized by similarities. Elements can be organized by the masses of their atoms. – PowerPoint PPT presentation

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Title: Elements make up the periodic table.


1
Elements make up the periodic table.
  • Section 1.2D

2
Elements can be organized by similarities.
  • Elements can be organized by the masses of their
    atoms.
  • Not all the atoms of an element have the same
    atomic mass elements have isotopes
  • Atomic mass of an element is the average mass of
    all the elements isotopes

3
Mendeleevs Periodic Table
  • 1800s several scientists tried to organize the
    elements based on their properties
  • 1860s Russian chemist Dmitri Mendeleev thought
    of how he could organize elements based on their
    physical and chemical properties
  • Arranged cards with the element, its atomic mass,
    and properties

4
Mendeleevs Periodic Table
  • Chart rows and columns
  • Rows elements showing similar chemical
    properties arranged rows so the atomic masses
    increased as you move down
  • Periodic Table shows a periodic, or repeating,
    pattern of properties of the elements
  • Mendeleevs Notebook

5
Predicting New Elements
  • Mendeleev left some empty spaces where no known
    elements fit the pattern.
  • He predicted that new elements that would
    complete the chart would eventually be
    discovered.
  • Many chemists found it hard to accept this, but
    six years later gallium was discovered and fit in
    the blank after aluminum
  • In the next 20 years, 2 other elements Mendeleev
    predicted were discovered.

6
The periodic table organizes the atoms of the
elements by properties and atomic number.
  • Modern periodic table differs from Mendeleevs
  • Elements with similar properties are found in
    columns, not rows.
  • The elements are not arranged by atomic mass but
    by atomic number.

7
Reading the Periodic Table
  • Each square of the periodic table gives
    particular information of the atoms of an
    element.
  • The number at the top of the square - atomic
    number the number of protons in the nucleus of
    an atom of that element
  • Chemical symbol an abbreviation for the
    elements name, which is written below the symbol
  • The number below the name atomic mass avg.
    atomic mass of all the isotopes of the element

8
Reading the Periodic Table
  • Color of the symbol the physical state of the
    element at room temp. (not always these colors)
  • White gas
  • Blue liquid
  • Black solid
  • The background colors of the squares indicate
    whether the element is a metal, nonmetal, or
    metalloid

9
Groups and Periods
  • Group elements in a vertical column of the
    periodic table that show similarities in their
    chemical and physical properties
  • Sometimes a group is called a family of elements,
    because these elements seem to be related.

10
Groups and Periods
  • Group 17 the halogen group
  • Tend to combine easily with many other elements
    and compounds, especially with the elements in
    Groups 1 and 2
  • Have some similarities, but their physical
    properties are not the same (ex. Flourine and
    chlorine are gases, bromine is a liquid, and
    iodine and astatine are solids at room temp.)
    related but not identical

11
Groups and Periods
  • Period each horizontal row on the periodic
    table
  • Properties of elements change in a predictable
    way from one end of a period to the other
  • Ex. Period 3 goes from metals to metalloids to
    nonmetals

12
Trends in the Periodic Table
  • An elements position in the table can give
    information about the element.
  • Atoms form ions by gaining or losing electrons
  • Atoms of elements on the left side of the table
    form positive ions easily (lose electrons)
  • Group 1 atoms lose and electron to form ions with
    one positive charge (1) and atoms in Group 2 can
    lose two electrons to form ions with a charge of
    2
  • Atoms of elements in Group 18 normally do not
    form ions
  • Atoms of elements in Group 17 often gain one
    electron to form a negative ion (1-) and atoms in
    Group 16 can gain two electrons to form a 2_ ion
  • Atoms of Groups 3 to 12 form positive ions, but
    the charge can vary

13
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14
Trends of the Periodic Table
  • Atomic size increases as you move down a group
    (column) and decreases as you move left to right
    across a period

15
Trends in the Periodic Table
  • Density generally increases from the top of a
    group to the bottom, but within a period, the
    elements at the far left and far right sides of
    the table are the least dense, and the elements
    in the middle are the most dense (osmium (Os) has
    the highest known density and is located at the
    center of the table)
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