The Periodic Table and the Atom

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The Periodic Table and the Atom

• Section 17.3

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SC Standards Covered

• Standard PS-2.3
• Explain the trends of the periodic table based
  on the elements valence electrons and atomic
  numbers.

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Dmitri Mendeleev

• arranged elements by atomic mass and similar
  properties
• published the first periodic table
• predicted the presence of undiscovered elements

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Henry Mosley

• arranged elements according to atomic number -
  periodic law
• fixed all the problems of earlier elements being
  out of order by properties

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The Atom and the Periodic Table
Groups - vertical rows - the elements in a
group have similar properties
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Electron Cloud Structure

• Electron clouds are arranged by energy levels
• Level 1 closest to the nucleus
• Maximum of 2 electrons
• Level 2 8 electrons
• Level 3 18 electrons
• Level n 2n2 electrons

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- Elements in the same group have the same number
of electrons in their outer energy level
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Groups and Valence Electrons

• Valence electrons electrons in the outermost
  energy level
• Group tells you the number of valence electrons
• Group 1 1 valence electron
• Group 2 2 valence electrons
• Group 13 3 valence electrons
• Group 18 8 valence electrons

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Rows on the Periodic Table

• Period the horizontal row on the periodic table
• The period on the periodic table that an element
  is in tells how many energy levels it has

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2e
8e
2e
Group 2 2 valence e- ? Period 3 3 energy
levels ?
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Drawing Models of Atoms

1. Determine the number of protons and electrons
   from the atomic number
2. Determine the number of neutrons from the mass
   number
3. Put the protons and neutrons in the nucleus
4. Using the period number draw the energy levels
   the atom has

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1. Put the valence electrons in the last energy
   level using the group number
2. Place remaining electrons in the lower energy
   levels

Draw atom models for the following elements 1.)
sulfur 33 2.) strontium - 88
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Groups on the Periodic Table

• Transition metals - groups 3 - 12

• Alkali metals - group 1A (except hydrogen)
• Most reactive metals
• Alkaline earth metals - group 2A
• inner transition metals (rare earth elements) -
  bottom two rows

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Halogens - group 17 - most reactive nonmetals
Noble gases - group 18 - nonreactive nonmetals
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Classifying the Elements

• Metals
• shiny, silver solids

• good conductors of heat and electricity
• malleable and ductile
• located to the left of the stair step line

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Nonmetals

• gases or dull, brittle solids
• poor conductors
• right of stair-step line

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Metalloids

• above and below stair-step line
• have properties of both metals and nonmetals