Trends

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Trends the Periodic Table
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Trends

• More than 20 properties change in predictable way
  based location of elements on PT
• Includes
• density, melting point, boiling point, atomic
  radius, ionization energy, electronegativity

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Atomic Radius

• Atomic radius defined as ½ the distance
  between neighboring nuclei in molecule or crystal
• size varies a bit from substance to substance

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X-ray diffraction pinpoints nuclei - measure
distance between them Cannot measure electron
cloud
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Trends Atoms get larger as go down column ?
principal energy levels Atoms get smaller as
move across series ? PPP proton pulling power
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Going down column 1
increasing energy levels as go down - makes
sense that atoms get larger in size
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Source Conceptual Chemistry by John Suchocki
Li Group 1 Period 2 Cs Group 1
Period 6
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Going across row 2
Atoms sizes actually get a bit smaller as you go
across a row Whats going on?
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What do you remember about charge?

• opposites attract
• like charges repel
• After principal energy levels, next largest
  influence on atomic size is proton pulling power
  (PPP)

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Effective nuclear charge

• Charge actually felt by valence electrons
• Atomic Number minus of inner shell electrons
• Not same as nuclear charge or protons in
  nucleus
• Charge felt by valence electrons is attenuated
  (shielded) by inner shell electrons

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H and He only elements whose valence electrons
feel full nuclear charge (pull)
Source Conceptual Chemistry by John Suchocki
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Source Conceptual Chemistry by John Suchocki
Lis valence e- feels effective nuclear charge of
1
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Source Conceptual Chemistry by John Suchocki
Calculating effective nuclear charge
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as go across row size tends to decrease a bit
because of greater PPP proton pulling power
Source Conceptual Chemistry by John Suchocki
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Source Conceptual Chemistry by John Suchocki
size ? as you go ? and size ? as you go ?
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Ionization Energy

• Amount energy required to remove valence
  electron from atom in gas phase
• 1st ionization energy energy required to remove
  most loosely held valence electron (e- farthest
  from nucleus)

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Trends in ionization energy

• What do you think happens to the ionization
  energy as go down column of PT?
• As go across row?

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?

• Valence electrons in atoms feel effective nuclear
  charge of 1
• Cs valence electron is lot farther away from
  nucleus
• electrostatic attraction much weaker so easier to
  steal electron away from Cs

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?

• easier to steal electron from Li than from Ne
• Li has smaller effective nuclear charge and
  valence electron is farther away from nucleus
• Li has less proton pulling power than Ne

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Trends in ionization energy

• Ionization energy decreases as go down a column
• easier easier to remove valence electron
• Ionization energy increases as go across a row
• more difficult to remove valence electron

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Periodic properties Graph shows a repetitive
pattern (Note Doesnt have to be a straight
line)
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Electronegativity

• ability of atom to attract electrons in bond
• noble gases tend not to form bonds, so they dont
  have electronegativities
• Unit Pauling
• Fluorine most electronegative element
• 4.0 Paulings

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Trends in electronegativity

• Related to PPP
• Increases as go across row
• Decreases as go down column
• Remember F is most electronegative element!

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Reactivity of Metals

• Metals are losers!
• judge reactivity of metals by how easily give up
  electrons
• most active metals are Fr (then Cs)
• For metals, reactivity increases as ionization
  energy goes down

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Trends for Reactivity of Metals or Metallic
Character

• Increases as go down
• Easier to lose electrons!
• Decreases as go across
• Harder to lose electrons!

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Reactivity of Non-metals

• Non-metals are winners!
• judge reactivity of non-metals by how easily gain
  electrons
• Fmost active non-metal
• For non-metals, reactivity increases as
  electronegativity increases

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Trend for Reactivity of Non-metalsDepends on
PPP

• Increases as go across
• Decreases as go down
• (Shielded by more inner-shell electrons)

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Ionic Size Relative to Parent Atom

• Depends if () ion or (-) ion
• How do you make a positive ion?
• How do you make a negative ion?

Remove electrons
Add electrons
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How do you know if an atom gains or loses
electrons?

• Think back to the Lewis structures of ions
• Atoms form ions to get a valence of 8
• (or 2 for H)
• Metals tend to have 1, 2, or 3 valence electrons
• Its easier to lose them
• Nonmetals tend to have 5, 6, or 7 valence
  electrons
• Its easier to add some
• Noble gases already have 8 so they dont form
  ions very easily

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Positive ions or cations

• Formed by loss of electrons
• Cations always smaller than parent atom

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Negative ions or anions

• Formed by gain of electrons
• Anions always larger than parent atom

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Allotrope

• Different forms of an element in the same phase
• Have different structures and properties
• O2 and O3 - both gas phase
• Graphite, diamond both solid phase carbon

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Graphite and Diamond