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Trends

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Trends & the Periodic Table – PowerPoint PPT presentation

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Title: Trends


1
Trends the Periodic Table
2
Trends
  • more than 20 properties change in predictable
    ways based location of elements on PT
  • some properties can be predicted
  • density
  • melting point/boiling point
  • atomic radius
  • ionization energy
  • electronegativity

3
Atomic Radius
  • Atomic radius defined as ½ distance between
    neighboring nuclei in molecule or crystal
  • size varies a bit from substance to substance

4
X-ray diffraction pinpoints nuclei then
measures distance between them Cannot measure
electron cloud
5
Trends Atoms get larger as go down column ?
principal energy levels Atoms get smaller as
move across series ? PPP proton pulling power
6
Going down column 1
increasing energy levels as go down - makes
sense that atoms get larger in size
7

Li Group 1 Period 2 Cs Group 1
Period 6
8
Going across row 2
size atoms actually get a bit smaller as go
across row left to right - whats going on?
9
What do you remember about charge?
  • opposites attract
  • like charges repel
  • largest influence on atomic size in order
  • principal energy levels
  • proton pulling power (PPP)

10
Effective nuclear charge
  • Charge actually felt by valence electrons
  • To calculate
  • Atomic Number minus inner shell electrons
  • Not same as nuclear charge or protons in
    nucleus
  • Charge felt by valence electrons is attenuated
    (shielded) by inner shell electrons

11
H and He only elements whose valence electrons
feel full nuclear charge (pull)
12

Lis valence e- feels effective nuclear charge of
1
13

Calculate effective nuclear charge
protons minus inner electrons
14
as go across row size tends to decrease a bit
because of greater proton pulling power (PPP)
15
  • size ? as you go ? column
  • size ? as you go ? row


16
Ionization Energy
  • Definition amount energy required to remove
    valence e- from atom in gas phase
  • 1st ionization energy energy required to remove
    most loosely held valence electron (valence e-
    farthest from nucleus)

17
Trends in ionization energy
  • What do you think happens to the ionization
    energy as go down column of PT?
  • As go across row?

decreases
increases
18
  • valence e- in atoms effective nuclear charge of
    1
  • Cs valence e- lot farther away from nucleus than
    Li
  • electrostatic attraction much weaker so easier to
    steal electron away from Cs


19
  • easier to steal electron from Li than from Ne
  • Li smaller effective nuclear charge
  • - valence electron farther away from
    nucleus
  • Li has less proton pulling power than Ne


20
Trends in ionization energy
  • Ionization energy decreases as go down column
  • easier to remove valence electron
  • Ionization energy increases as go across row
  • more difficult to remove valence electron

21
Periodic properties Graph shows a repetitive
pattern (Note Doesnt have to be a straight
line)
22
Electronegativity
  • ability of atom to attract electrons in bond
  • noble gases tend not to form bonds, so dont have
    electronegativity values
  • Unit Pauling
  • Fluorine most electronegative element
  • 4.0 Paulings

23
Trends in electronegativity
  • Related to PPP
  • Increases as go across row
  • Decreases as go down column
  • Remember F most electronegative element!

24
(No Transcript)
25
Reactivity of Metals
  • metals are losers!
  • judge reactivity of metals by how easily give up
    electrons
  • most active metals Fr (then Cs)
  • For metals, reactivity increases as ionization
    energy goes down

26
Trends for Reactivity of Metals or Metallic
Character
  • Increases as go down column
  • easier to lose electrons!
  • Decreases as go across row
  • more difficult to lose electrons!

27
Reactivity of Non-metals
  • Non-metals are winners!
  • judge reactivity of non-metals by how easily gain
    electrons
  • F most active non-metal
  • For non-metals
  • reactivity ? as electronegativity ?

28
Trend for Reactivity of Non-metalsDepends on
PPP
  • Increases as go across row
  • Decreases as go down column
  • (shielded by more inner-shell electrons)

29
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
30
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
  • Non-metals 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

31
Positive ions (cations)
  • Formed by loss of electrons
  • Cations always smaller than parent atom

32
Negative ions or (anions)
  • Formed by gain of electrons
  • Anions always larger than parent atom

33
Allotropes
  • Different forms of element in same phase
  • different structures and properties
  • examples C and O

34
O2 and O3 - both gas phase
  • O2 (oxygen) - necessary for life
  • O3 (ozone) - toxic to life

35
  • Graphite, diamond
  • both carbon in solid form

36
Graphite and Diamond both carbon in solid form
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