development of the periodic table

• Who is credited with the modern periodic table

  Dmitri Mendeleev
• What do we call group 7 elements

  halogens
• What happens to the reactivity as you move down group 7

  the reactivity decreases
• Roughly how many elements are in the periodic table

  118
• How many electrons in the outer shell will an element in group 3

  3
• Where do you find the metals in the periodic table

  • On the left and in the middle.
• How is the periodic table arranged

  Order of increasing atomic number
• What happens to the reactivity as you move down group 1

  it increases
• What should you be able to describe by the end of the video?

  Early attempts to arrange elements
• Why is the periodic table called 'periodic'?

  Elements occur at regular intervals
• 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 the same group have similar chemical properties?

  They have the same number of outer electrons
• Who first noticed that 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 every eighth element?

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

  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 unique?

  Switched order of elements 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 is the modern periodic table different from Mendeleev's?

  Arranged by atomic number instead of weight
• What is the atomic number?

  Number of protons in an element
• What problem did ordering by atomic weight create?

  Elements could appear in the wrong order
• How does ordering by atomic number resolve the issue?

  It places elements in the correct groups
• What additional group does the modern periodic table have?

  Group zero, the noble gases
• Why were noble gases not included in Mendeleev's table?

  They had not been fully discovered