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A. Dmitri Mendeleev
Dmitri Mendeleev (1869, Russian)
• Organized elements by
increasing atomic mass.
• Predicted the existence of
undiscovered elements.
B. Henry Mosely
Henry Mosely (1913, British)
• Organized elements by
increasing atomic number.
• Fixed problems in Mendeleev’s
arrangement.
B. Table Sections
1
2
3
4
5
6
7
Lanthanides - part of period 6
Actinides - part of period 7
Overall Configuration
Alkali Metals
1
2
3
4 5
6
7
• Soft and shiny• React violently with water• 1 valence electron• Forms ions with +1 charge• 1+ is oxidation number
Alkaline Earth Metals
1
2
3
4 5
6
7
• Have 2 valence electrons• Form ions with +2 charge• Less reactive than alkali metals• 2+ is oxidation number
Halogens
1
2
3
4 5
6
7
• Has 7 valence electrons• Forms ions with -1 charge• 1- is oxidation number• Very reactive
Noble Gases
1
2
3
4 5
6
7
• Have full octet (8) of valence electrons (except Helium which has 2)
• Called “inert gases” because they don’t tend to react
Periodic Law
• Properties of elements repeat
periodically when the elements are
arranged by increasing atomic
number.
A. Terms
A. Terms
Valence Electrons
• e- in the outermost energy level Atomic Radius
First Ionization Energy
• energy required to remove an e- from a neutral atom
B. Periodic Trends Group # = # of valence e- (except He)
• Families have similar reactivity. Period # = # of energy levels
1A
2A 3A 4A 5A 6A 7A
8A