Periodicity

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Periodicity

• Glencoe
• Chapter 6

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Developmentof theModern Periodic Table

• 1790s 23 known elements
• By 1870s 70 known elements
• 1864 - John Newlands proposed arrangements by
  mass and properties by octaves
• 1864 Lothar Meyer proposes arrangements by mass
  and columns of propertiesbut doesnt publish!
• 1869 Dmitri Mendeleev also proposed
  arrangements by mass and columns of
  propertiesand announces!
• 1913 Henry Moseley proposed arrangements by
  atomic number. (periodic law)

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Newlands octaves
H 1 F 8 Cl 15 Co/Ni 22 Br 29 Pd 36 I  42 Pt/Ir 50
Li 2 Na 9 K 16 Cu 23 Rb 30 Ag 37 Cs 44 Tl 53
Gl 3 Mg 10 Ca 17 Zn 25 Sr 31 Cd 34 Ba/V 45 Pb 54
Bo 4 Al 11 Cr 18 Y 24 Ce/La 33 U 40 Ta 46 Th 56
C 5 Si 12 Ti 19 In 26 Zr 32 Sn 39 W 47 Hg 52
N 6 P 13 Mn 20 As 27 Di/Mo 34 Sb 41 Nb 48 Bi 55
O 7 S 14 Fe 21 Se 28 Ro/Ru 35 Te 43 Au 49 Os 51
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Shortly after, his ideas were presented to the
Russian Physico-chemical Society. They were read
by Professor Menschutkin because Mendeleev was
ill. His ideas were then published in the main
German chemistry periodical of the time,
Zeitschrift f?r Chemie.
                                                  
                                                  
                                                  
                                                  
                                         The
worlds first view of Mendeleevs Periodic Table
an extract from Zeitschrift f?r Chemie, 1869.
Click here for a translation
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Key landmarksof themodern periodic table

• Periods (horizontal)
• Groups/families (vertical)
• Representative elements
• s p block
• Groups 1A 8A
• Groups 1,2,13,14,15,16,17,18
• Transition elements
• d block (f block inner transition elements)
• Groups 1B 8B
• Groups 3 - 12

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Other notable classifications

• Metals
• Alkali (group 1)
• Alkaline (group 2)
• Metalloids
• Nonmetals
• Halogens (group 17)
• Noble gases (group 18)

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Organizing Elements by Electron Configuration

• Valence Electrons
• Atoms in the same group have similar chemical
  properties b/c they have the same if valence
  electrons
• Valence Electrons and Periods
• Energy level of valence electrons indicates the
  period on the PT
• Valence Electrons and Group Number
• Group valence electrons
• Exception Helium

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• The s-, p-, d-, and f- block elements
• s-block
• p-block
• d-block
• f-block

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Periodic trends

• Vary systemically
• across a period (horizontally)
• along a group (vertically)

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Atomic radii

• Based on probability of electron cloud,
  therefore, defined by how closely an atom lies to
  a neighboring atom
• DECREASES to the right across a period
• Due to larger nuclear attraction
• INCREASES down a group
• Due to more layers of electrons

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Ionic Radii

• Ions (charged atoms) form when electrons are
  gained or lost.(the number of protons and
  electrons dont match!)
• DECREASES to the right across a period (in two
  phases)
• INCREASES down a group

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Ionization Energy

• Defined as amount of energy required to remove
  an electron from a gaseous atom
• 1st ionization energy
• 2nd ionization energy
• Etc.
• Think of this as the atoms ability to hold onto
  its valence electron!
• INCREASES across a period
• Harder to remove e-
• Positive energy means harder
• DECREASES down a group
• Easier to remove e-
• More negative energy means easier or more
  stable

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Element I1 I2 I3 I4 I5 I6 I7
Na 490 4560          
Mg 735 1445 7730        
Al 580 1815 2740 11,600      
Si 780 1575 3220 4350 16,100    
P 1060 1890 2905 4950 6270 21,200  

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Octet Rule

• Atoms tend to gain, lose, or share electrons in
  order to acquire a full set of eight valence
  electrons
• Note chemical stability of noble gases
• Predicts ionic charge of main block elements
• CATIONSpositively charged ions (lost e-)
• ANIONSnegatively charged ions (gained e-)

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Electron Affinity

• Energy associated with adding an electron to an
  atoms electron cloud---think of the opposite of
  Ionization Energybut same effect!
• INCREASES (but the energy gets more negative
  means more stable) across period
• DECREASES (but the energy value gets more
  positive means more difficult) down group
• Therefore, a great idea!....

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Electronegativity

• Indication of the relative ability of the atom to
  attract electrons in a chemical bond
• Think of this quantity as how strongly an atom
  might want to gain an electron.
• Arbitrary rating scaled to 4.0..
• Most electronegative element is fluorine with
  3.98
• INCREASES across a period
• DECREASES down a group

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Summary of Trends