Atomic History and Structure

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Atomic History and Structure

• Chapter 4

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Early Theories of The Atom
DemocritusDemocritus (b. c. 460 BC d. c. 370 BC)
postulated the existence of invisible atoms,
characterized only by quantitative properties
size, shape, and motion. Imagine these atoms as
indivisible spheres, the smallest pieces of an
element that still behave like the entire chunk
of matter.

Thomson
Rutherford
Dalton
The PLUM PUDDING MODEL
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Rutherfords Experiment

• Visit this website and click on the tutorial for
  Section 3.2 Rutherford Experiment Play and
  watch through all 5 parts
• Visit this website and see what Rutherfords
  Experiment looked like.

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What is an ATOM?

• Atom- the smallest particle of an element that
  retains the properties of that element
• Subatomic particles
• Protons Positive charge, found in the nucleus
  and have a mass of 1 amu. ( Identify)
• Neutrons- No charge, found in the nucleus, and
  have a mass of 1 amu ( Isotopes)
• Electrons- Negative charge, found in the energy
  levels outside of the nucleus, have relatively no
  mass ( Ions)

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By the Numbers

• Atomic number
• This determines the elements position in the
  periodic table ( Identifies the atom)
• In atoms not ions
• Atomic protons of electron
• Mass number-
• Mass number protons neutrons
• Why are electrons not included in the mass of an
  atom?
• You will not look to the periodic table to
  determine the mass number, the number on the
  periodic table is an average.

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Isotopes-

• An Isotope is the same element (at.) with a
  different number of neutrons.
• When naming an isotope you write name of the of
  the element, dash, then write the mass number
• Example Carbon-14

Symbol of element
Atomic number from periodic table
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More about the mass

• Knowing the mass number you can determine the
  number of neutrons in a specific atom
• of neutrons mass number - of protons
• atomic mass unit (amu)- the mass of the carbon
  atom.

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Isotopic Notation

• Isotope notation
• Example 1
• Carbon-14 C
• Carbon-12 C
• Determine the number of protons, electrons and
  neutrons in an isotope.
• Examples H H H
• What number is different?

Check your work!
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Calculating Atomic Mass

• Atomic mass- weighted average mass of the
  isotopes of that element.
• This is the decimal number on the periodic table.
• To determine the atomic mass you must know what
  percent of each isotope of the element is found
  in nature and then it can be calculated.
• Example For Chlorine
• 25 is chlorine-37
• 75 is chlorine 35
• What is the average atomic mass of chlorine?

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To Calculate

• 25 is chlorine-37
• 75 is chlorine-35
• Take mass 37 x .25 ans A
• Take mass 35 x .75 ans B
• Add ansA ansB Average Atomic mass for
  Chlorine

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Ions-a charged particle

• An atom that has either gained or lost an
  electron. Electrons are lost and gained to make
  ions
• When they are gained (-Neg) ions (anion)
• When they are lost ( Pos) ions (cations)

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Ion Examples

• Example
• What is the charge of an ion that has 11 protons
  and 10 electrons. Write the isotope notation for
  this atom.
• Tell the number of P, E and N in the following
  ions.

p7 n8 e10
p12 n12 e10
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History of Periodic Table

• Dmitri Mendeleev listed the elements in several
  vertical columns in order of increasing atomic
  MASS. He left blanks in the table for elements
  that were not discovered yet.
• Henry Mosley Arranged elements on the periodic
  table in order of increasing atomic NUMBER.

http//www.chemheritage.org/EducationalServices/ch
emach/ppt/lm04.html
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Arrangement of Periodic Table

• Periodic law the properties of elements are
  periodic functions of their atomic number
• Periods horizontal rows 7 correspond to
  energy levels
• Groups/Families vertical columns group A
  Roman numerals correspond to the number of
  valence electrons
• Group I Alkali metals, Group II Alkaline
  earth metals, Group VII Halogens, Group VIII
  Noble gases

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Metals, Nonmetals, and Metalloids

• Metals everything to the left of the stairstep
  including aluminum does not include hydrogen
• Properties Have luster (shiny), good conductors
  of heat and electricity, malleable ( able to be
  pounded into sheets), ductile (able to be pulled
  into a wire), tend to lose electrons in chemical
  reactions, most are solids
• Transition metals middle block over to
  stairstep
• Inner transition metals bottom 2 rows
  sometimes called lanthanide series and
  actinide series

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Metals, Nonmetals, and Metalloids

• Nonmetals everything to the right of the
  stairstep includes hydrogen
• Properties Dull, poor conductors, brittle, tend
  to gain or share electrons in chemical reactions,
  most are gases
• Metalloids either side of the stairstep does
  not include aluminum

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Periodic Table colored to show metals, nonmetals,
and metalloids
http//hyperphysics.phy-astr.gsu.edu/hbase/pertab/
pertab.html
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Answers to practice problems

• Example
• Isotopes of Hydrogen

The mass number differs due to the difference in
neutrons!
Back to isotopic notation