Development of the periodic table

• What are the groups in the periodic table?

  Columns of elements with similar properties
• What does group one of the periodic table consist of?

  Highly reactive metals like lithium
• What does group seven of the periodic table consist of?

  Highly reactive nonmetals like fluorine
• Why do elements in a group have similar chemical properties?

  They have the same number of outer electrons
• Who first noticed elements with similar properties occurred in threes?

  Johan Dober
• What did Dober call the groups of three elements?

  Triads
• What did John Newlands arrange the elements by?

  Increasing atomic weight
• What did Newlands observe about every eighth element?

  They reacted in a similar way
• What did Newlands call his observation about the elements?

  Law of octaves
• What was a problem with Newlands' law of octaves?

  Elements were grouped with different properties
• Who developed the first modern periodic table?

  Dmitri Mendeleev
• How did Mendeleev arrange the elements?

  In order of increasing atomic weight
• What two things did Mendeleev do that were innovative?

  Switched element order and left gaps
• Why did Mendeleev leave gaps in his periodic table?

  He predicted undiscovered elements' existence
• What happened when the missing elements were discovered?

  Their properties matched Mendeleev's predictions
• How are elements arranged in the modern periodic table?

  By increasing atomic number
• What is the significance of atomic number in the modern periodic table?

  It ensures elements are in the correct group
• What problem did Mendeleev's atomic weight ordering cause?

  Elements could appear in the wrong order
• What is group zero in the modern periodic table?

  Noble gases
• What was not fully discovered when Mendeleev published his table?

  The noble gases
• What are the key differences between Mendeleev's and the modern periodic table?

  • Mendeleev arranged by atomic weight
  • Modern table arranges by atomic number
  • Modern table includes group zero (noble gases)
• What are the historical attempts to arrange elements before Mendeleev?

  1. Dober's triads: elements in threes
  2. Newlands' law of octaves: every eighth element similar
  3. Issues with grouping by atomic weight