Pearson Prentice Hall Physical Science: Concepts in Action

1
Pearson Prentice Hall Physical Science Concepts
in Action

• Chapter 5
• The Periodic Table

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5.1 Organizing the Elements

• Objectives
• 1. Explain how Mendeleev organized the periodic
  table
• 2. Describe the evidence that helped verify the
  usefulness of Mendeleevs table

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Mendeleevs Organization

• Mendeleev arranged the elements in order of
  increasing mass
• Elements with similar properties were in the same
  column by using this arrangement
• Definition a periodic table is an arrangement of
  elements in columns based on a set of properties
  that repeat from row to row

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Evidence for the Mendeleev Table

• Mendeleev used his organization of the table to
  predict where undiscovered elements would fit
• He deliberately left spaces or gaps in the table
  for these elements
• As new elements were discovered, Mendeleevs
  prediction proved to be correct
• The close match between the predictions and the
  actual properties of new elements showed how
  useful his periodic table could be

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5.2 The Modern Periodic Table

• Objectives
• 1. Describe how the modern periodic table is
  organized
• 2. Explain what atomic mass of an element depends
  on
• 3. Compare the categories that are used to
  classify elements on the periodic table
• 4. Distinguish how properties vary across a
  period in the periodic table
• http//www.webelements.com/index.html

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Organization of the Modern Periodic Table

• In the modern periodic table, elements are
  arranged by increasing atomic number
• Atomic number is the number of protons
• Each ROW of the table is a PERIOD
• Each COLUMN is a GROUP or FAMILY
• Properties of elements repeat predictably when
  atomic numbers are used to arrange elements in
  groups
• Definition periodic law is the predictable
  pattern of repeating properties in the periodic
  table

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Atomic Mass

• Atomic mass is a value that depends in the
  distribution of an elements isotopes in nature
  and the masses of those isotopes
• Definition an atomic mass unit (amu) is one
  twelfth the mass of a carbon-12 atom
• Mass is given in grams
• Scientists assigned 12 atomic mass units (amu) or
  12 g to the carbon-12 atom which has 6 protons
  and 6 neutrons
• Each proton and each neutron weighs one gram
• Electron mass is small and is ignored under this
  system

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• Definition an isotope of an element has a
  different number of neutrons in its nucleus
• Since mass is given by protons plus neutrons,
  isotopes of an element have different masses
• It is still the same the element, however,
  because the number of PROTONS remains unchanged
• The number of protons determines which element
  you have

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• Most elements exist as a mixture of two or more
  isotopes
• http//yteach.co.uk/page.php/resources/view_all?id
  atom_atomic_number_mass_nuclei_symbol_isotope_ele
  ctron_proton_t_page_8fromsearch
• Atomic mass is determined by the weighted average
  of all the isotopes
• The weighted average takes into account how often
  the isotope occurs by using percentages
• The more often an isotope occurs, the more it
  contributes to the final atomic mass calculation

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3 Categories to Classify Elements

• Elements are classified as metals, nonmetals and
  metalloids
• Metalloids are also called semiconductors
• Metals are good conductors, ductile (can be drawn
  into wires), malleable, shiny, solid (with the
  exception of mercury)
• Transition metals (flat part of the table) tend
  to form compounds with color
• Nonmetals are poor conductors, have low boiling
  points tend to be gases
• Metalloids or semiconductors have properties of
  both metals nonmetals

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How Properties Vary Across the Table

• Periods are the rows
• Across a period from left to right, the elements
  become less metallic and more nonmetallic

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5.3 Representative Groups

• Objectives
• 1. Explain why elements in a group have similar
  properties
• 2. Describe some properties of the Group A
  (representative) elements

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Similar Properties in a Group

• Definition a valence electron is an electron
  that is in the highest occupied energy level of
  an atom
• Valence electrons are the electrons in the outer
  shell
• Elements in a group have similar properties
  because they have the same number of valence
  electrons
• Elements seek to have complete outer shells with
  8 electrons
• Therefore, the number of valence electrons
  determines how reactive the element is

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Group A

• Group 1A are the alkali metals
• The reactivity of alkali metals increases from
  the top of Group 1A to the bottom
• Group 1A has one valence electron (charge is 1)
• Group 2a are the alkaline earth metals
• Differences in reactivity among the alkaline
  earth metals are shown by the ways they react
  with water calcium, strontium barium react
  easily
• These elements have 2 valence electrons (charge
  is 2)

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• Group 3A is the boron family
• Aluminum is in this family it is the most
  abundant METAL in earths crust
• Group 3A has 3 valence electrons (charge is 3)
• Group 4A is the carbon family
• The carbon family has 4 valence electrons
• Except for water, most of the compounds in your
  body contain carbon
• These elements are reactive and will either give
  up their 4 valence electrons or share 4 valence
  electrons with other elements (charge is either
  4 or -4)

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• The nitrogen family is Group 5A
• Group 5A has 5 valence electrons which it can
  give up (charge 5)
• Group 5A can also take in 3 additional electrons
  from other elements which make a charge of -3
• This group is a mixture one metal plus nonmetals
  metalloids
• The oxygen family is Group 6A
• It has both nonmetals metalloids
• Oxygen is most abundant ELEMENT in the earths
  crust
• These elements have 6 valence electrons
• They seek to acquire 2 more electrons and the
  family charge is -2 for these elements

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• Group 7A are the halogens
• halo means salt gen comes from genesis
  which means beginning or formation
• Halogens are salt formers
• They readily react with metals
• Their 7 valence electrons means they seek one
  additional electron, giving their family a charge
  of -1

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• Group 8A are the noble gases
• The nobles are colorless, odorless and unreactive
  because they have 8 valence electrons in their
  outer shell
• Since their outer shell is complete their charge
  is 0
• The nobles are also called the zero elements