ATOMIC STRUCTURE

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CHAPTER 4.4-4.6

• ATOMIC STRUCTURE
• and the PERIODIC TABLE

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Distinguishing Between Atoms

• Atomic Number
• Unique for each element.
• Equal to the number of protons in the nucleus of
  an atom of that element.
• The number of protons must equal the number of
  electrons.

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Distinguishing Between Atoms

• Mass Number
• Mass is concentrated in the nucleus
• Depends on the number of protons and neutrons.

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Distinguishing Between Atoms

• Determining atomic composition from mass number
  and atomic number
• Number of protons number of electrons Atomic
  number
• Number of neutrons mass number number of
  protons.

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Distinguishing Between Atoms

• Representing atomic composition using atomic
  number and mass number

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Distinguishing Between Atoms

• Elements can also be represented using name and
  mass number
• Carbon - 12

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Distinguishing Between Atoms
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Distinguishing Between Atoms
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Distinguishing Between Atoms

• Isotopes
• Equal number of protons and electrons.
• Different number of neutrons
• Different mass number
• Chemically alike

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Distinguishing Between Atoms

• Atomic Mass
• Mass of proton or neutron is small (1.67 x
  10-24 g)
• Mass of electron is negligible in comparison
  (9.11 x 10-28 g)
• The mass of even the largest atom is incredibly
  small

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Distinguishing Between Atoms

• Compare relative mass using a reference isotope
  as a standard
• Isotope C-12 assigned a mass of 12 amu
• Atomic mass unit (amu) defined as one-twelfth the
  mass of carbon-12

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Distinguishing Between Atoms

• If atomic mass is determined by the number of
  protons and electrons, why isnt the mass of an
  element a whole number?
• Most elements occur as a mixture of two or more
  isotopes.

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Isotopes of hydrogen

• Hydrogen 1 (protium 99.98)
• Hydrogen 2 (deuterium 0.0156)
• Hydrogen 3 (tritium trace quantities)

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Protium

• 1 proton
• 1 electron
• 0 neutrons

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Deuterium

• 1 proton, 1electron, 1neutron
• D2O heavy water
• Concentrated with neutrons during slow
  electrolysis of water
• Greater density and higher boiling point then H2O
• Not radioactive

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Tritium

• 1 proton, 1 electron, 2 neutrons
• Formed continuously in upper atmosphere in
  nuclear reactions by cosmic rays
• Compounds can be labeled with D or T by comparing
  the location of the heavy Hydrogen

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Distinguishing Between Atoms

• The atomic mass of an element is a weighted
  average mass of the atoms in a naturally
  occurring sample of the element.

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Distinguishing Between Atoms

• You can calculate the atomic mass if you know
  three values
• The number of stable isotopes of the element.
• The mass of each isotope.
• The natural percent abundance of each isotope.

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Distinguishing Between Atoms

• Chlorine, symbol Cl, has two isotopes
• Cl-35 (34.97) abundance 75.77
• Cl-37 (36.97) abundance 24.23
• Calculate the atomic mass of chlorine

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Mass Defect missing mass?

• Masses of particles that make up an atom are
  added, the sum is always larger than the actual
  mass of the atom.
• The missing mass is the matter converted into
  energy when the nucleus was formed from its
  component protons and neutrons.

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Mass Defect

• Calculate the mass defect of a chlorine-35 atom.
• The actual mass of chlorine-35 is 5.81 x 10-23
  grams
• e 9.11 x 10-28 g
• p 1.67 x 10-24 g
• n 1.67 x 10-24 g

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The Periodic Table

• Dmitri Mendeleev (1834-1907)
• Russian chemist
• Listed elements in columns in order of increasing
  atomic mass.
• Arranged columns so that elements with similar
  properties were side by side.

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The Periodic Table

• Medeleev left blank spaces where there were no
  known elements with the appropriate properties or
  mass.
• Predicted the properties of the missing elements.

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The Periodic Table

• Henry Mosely (1887-1915)
• British Physicist
• Determined the atomic number of the atoms of the
  elements.
• Arranged elements in table by atomic number
  instead of mass.

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The Modern Periodic Table

• Each horizontal row is a period
• Seven periods
• From 2 to 32 elements in a period
• Properties of the elements change as you move
  across a period.
• This pattern repeats from period to period
• The Periodic Law

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The Modern Periodic Table

• Each column is a group or family
• Elements in a group have similar physical and
  chemical properties.
• Groups are identified by a number and the letter
  A or B
• Group A are the representative elements
• Group A can be divided into three broad classes

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The Modern Periodic Table

• Metals
• High electrical conductivity
• High luster when clean
• Ductile
• malleable

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The Modern Periodic Table

• Metals
• Alkali metals
• Alkaline earth metals
• Transition metals
• Inner transition metals

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The Modern Periodic Table

• Non-Metals
• poor electrical conductivity
• Non-lustrous

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The Modern Periodic Table

• Non-Metals
• halogens
• Noble gases

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The Modern Periodic Table

• Metalloids
• Elements with properties that are intermediate
  between those of metals and non-metals.