Elements make up the periodic table.

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Elements make up the periodic table.

• Section 1.2D

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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

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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

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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

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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.

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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.

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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

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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

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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.

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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

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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

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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

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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

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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)