Lecture 5.2 - Periodic Properties 2

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    Periodic Properties of the

    Elements

    Part 2

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    Ionization Energy (continued)

    1st I.E. = I1

    2nd I.E. = I2

    3rd I.E. = I3

    ( ) ( )energy X Xg g e+

    + +

    2( ) ( )energy X Xg g e+ +

    + +

    2 3( ) ( )energy X Xg g e

    + + + +

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    When e- is removed from an atom, therepulsion among remaining e- s

    decreases

    More energy is required to removesubsequent e-

    I1 < I2 < I3 <

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    I1 = 580 kJmol-1

    I2 = 1817 kJmol-1

    I3 = 2740 kJmol-1

    ( ) ( )Al Alg g e+

    +

    2

    ( ) ( )Al Alg g e+ +

    +

    2 3

    ( ) ( )Al Alg g e+ +

    +

    Why?

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    Al

    Zeff = 13 12 = +1

    1+

    I1 = 580 kJmol-1

    Zeff = 13 10 = +3

    I2 = 1817 kJmol-1

    2+3+

    I3 = 2740 kJmol-1

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    Al 1+ Zeff = 13 10 = +3

    I2 = 1817 kJmol-1

    I3 = 2740 kJmol-1

    Why is I3 > I2even though Zeff is same?

    e- pair repulsion

    2nd e- is easier to remove

    2+

    I2

    = 1817 kJmol-1

    3rd e- no longerfeels repulsion

    3+

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    Al 3+

    Zeff = 13 4 = +9Al 3+

    I4 = 11,575 kJmol-1

    4+

    I4 >> I3because e- is removed

    from lower energy subshell

    What about I4?

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    Higher ionization energies Ionization energy

    always increasesas you pull offmore electrons.

    Ionization energiestake a huge leapwhen we try toremove an electron

    from a new innersubshell.

    Zeff increases dramatically at each lower subshell,

    thus more energy is required to overcome the

    attractive force between e- and nucleus

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    Higher ionization energies

    A: Al3+ has a stable e- configuration andthus more energy (I4) is required to remove

    the fourth e-

    FAIL

    Q: For Al whyis I

    4

    > I3

    ?

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    Account for

    differencesin I1, I2, & I3

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    Exception 1: N vs O and P vs S

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    Trend: I1 N < I1 O

    Reality: I1 N > I1 O

    Why?

    e- pair repulsion - Less energy required toremove 1st e-

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    Without e- repulsion, I2 obeys periodic trend

    I2 N I2 O I1 S and I2 P < I2 S for same reason

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    Exception 2: Be vs B and Mg vs Al

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    Zeff = 4 2 = +2

    Zeff = 5 4 = +1

    Lower Zeff Lower I1

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    Electron Affinity (E.A.) The energy change that occurs when an electron is added to an

    atom (or ion) in the gaseous state. X(g) + e- X-(g) kJmol-1

    Frequently costs nothing but actually yields energy therefore EAsare usually exothermic

    H < 0 because X(g) is less stable (high PE) than X-(g) (lower PE)

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    O(g) + e- O-(g)

    unstable(high PE)

    Less unstable + Energy(lower PE)

    unstable stable + Energy

    F(g) + e- F-(g)

    Thus E.A. F > E.A. O

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    E.A. increases (more - )

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    Electronegativity (E.N.)

    The ability of an atom to attract pairs ofelectrons toward itself in a covalent bond

    A property of an atom in a molecule

    takes into account atomic radius, mass,

    electron affinity

    Electron greed; the higher the E.N. the

    more greedy an atom is

    Atom with higher E.N. will pull shared e-

    (electron density) closer to itself

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    First proposed by Linus Pauling in 1932asa development ofvalence bond theory

    Pauling Scale of E.N.ranges from 0.7 (Fr) to 4.0 (F)

    E.N. differences determine

    bond polarity

    In a molecular formula, the

    element with lowest E.N. is

    written first; element with

    highest E.N. is written last

    (except H in acids)

    http://upload.wikimedia.org/wikipedia/commons/d/db/Pauling.jpg
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    E.N. increases

    Pauling Scale Values for Electronegativity

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    Zeff, I.E., E.A., E.N. increases

    A.R. , I.R.

    decreases

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    Break

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