The Atom

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• Unit
• The Atom
• and
• The Periodic Table

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Evolution of the Structure of an Atom
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Daltons Atomic Theory

• All elements are composed of indivisible
• particles called atoms
• Atoms of the same element are identical. The
  atoms of any one element are different from those
  of any other element.
• Atoms of different elements can physically mix
  together or chemically combine with one another
  in simple whole number ratios to form
  compounds.(law of definite composition)
• Chemical rxns occur when atoms are separated,
  joined, or rearranged. Atoms of one element,
  however, are never changed into atoms of another
  element as a result of a chemical reaction.(law
  of conservation of mass)

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J.J. Thomson

• discovered the electron
• plum pudding model

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Rutherford

• discovered the nucleus
• Proposed electrons surround the nucleus in a cloud

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The Atom Today

• The atom is the smallest particle of an element
  that retains the properties of that element
• Atoms can only be seen with proper
  instrumentation
• Daltons Atomic Theory wasnt completely correct
• Atoms can be broken down into subatomic particles
• Atoms of the same element are not identical

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Properties of Subatomic Particles
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Distinguishing Between Atoms
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Atomic Number

• Number of protons in the nucleus of an atom
• Identifies the element
• Elements are listed on periodic table according
  to atomic number

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Atomic Number
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Atomic Number
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Atomic Number

• atoms are electrically neutral
• protons electrons

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Mass Number

• total number of protons and neutrons in an atom
• It is not found on the periodic table but can be
  estimated

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Shorthand Notation
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Fill in the following table
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Isotopes

• Atoms that have the same number of protons but
  different numbers of neutrons
• Differ in their mass number

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Isotopes

• the existence of isotopes was not predicted by
  Dalton, who said atoms of the same element are
  the same

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Isotopes

• identified by their mass , write the name of
  the element then a hyphen with the mass number

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Isotopes
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Uses of Isotopes

• C-14 archeological carbon dating
• Am-241 smoke alarms
• I-131 treating thyroid disorder
• Co 60 cancer treatment

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Atomic Mass (atomic weight)

• weighted average mass of the atoms in naturally
  occurring samples of the element

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Atomic Mass

• reflects the mass and the relative abundance of
  isotopes as they occur in nature

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Atomic Mass

• To calculate the atomic mass of an element
  multiply the atomic mass of each isotope of the
  element by its relative abundance, then add the
  results
• atomic mass mass1relabd.1 mass2rel.abd.2...

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1. Calculate the abundance of fictitious
element Nv2. If the mass of 293Nv is 293.15 amu
(red)and that of 295Nv is 295.15 amu
(blue), what is the atomic mass of Nv? .
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Periodic Table

• _______________ was the first person to find a
  way to list elements in order of increasing
  atomic mass

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Periodic Table

• He constructed the first periodic table in 1869,
  an arrangement of the elements according to
  similarities in their properties.

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Mendeleevs Periodic Table
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Periodic Table

• In 1913, ______ determined the atomic number of
  atoms and arranged the modern periodic table
  according to atomic number .

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Modern Periodic Table
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Modern Periodic Table

• Each element is identified by its symbol placed
  in a square

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Modern Periodic Table

• The horizontal rows of the periodic table are
  called _____
• There are ___

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Modern Periodic Table
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Modern Periodic Table

• Each vertical column is called a ____ or ____
• There are ____.

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Modern Periodic Table
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Periodic Table

• A periodic law means that physical and chemical
  properties of elements are functions of their
  atomic numbers
• Elements in the same group on the periodic table
  have similar properties

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Modern Periodic Table

• Group A elements are called the representative
  elements because they have a wide range of
  chemical and physical properties
• Name the groups in Group A

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Modern Periodic Table

• Group B elements are called the ______________
• The inner transition elements are the ______ and
  _____

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Modern Periodic Table
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Modern Periodic Table

• The representative elements can be divided into
  three broad classes Metals, Nonmetals, and
  Metalloids
• What are some characteristics of each?

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Modern Periodic Table
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Niels Bohr

• credited for a model of the atom that states that
  electrons are at specific distances from the
  nucleus of an atom

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Bohr Models
Energy Level 1 2 3 4
ELECTRONS        
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Bohr Models

• Exception Outermost energy level can only hold
  up to 8e-
• You need to be able to diagram Bohr models for
  1-36 excluding transition elements

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Bohr Models

• Do you notice any trends with the group or
  period of the periodic table?

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Bohr Models

• Trends
• Group numbers (1-8A) predict valence electrons
  (electrons in the outmost level).
• 2. The period tells you how many energy levels
  you have in the atom.

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