Transcript Ionization Enthalpies of Elements

Chapter 5
Electronic Configurations
and the Periodic Table
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New Way Chemistry for Hong Kong A-Level Book 1
Ionization Enthalpies of Elements
Ionization enthalpy of an atom is governed by the followings:
1. Half-filled or completely filled sub-shells have extra stability.
2. Nuclear charge
more protons  stronger attraction to electrons  more
difficult to ionize.
3. Screening/shielding effect
repulsion between outermost electrons and electrons in inner
shells. The nucleus is ‘screened’ and its attraction decreases.
4. Atomic radius
larger atomic size  distance between outermost electrons and
nucleus increases  attraction decreases.
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New Way Chemistry for Hong Kong A-Level Book 1
4.2 Deduction of Electronic Structure from Ionization Enthalpies (p.93)
Evidence of Sub-shells
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 116)
•
Moving across a period, there is an increase in the
nuclear attraction due to the addition of proton in
the nucleus.
•
The added electron is placed in the same quantum
shell. The shielding effect does not increase much.
•
The increase in nuclear attraction outweighs the
increase in the shielding effect between the
electrons
an increase in the effective nuclear charge.
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New Way Chemistry for Hong Kong A-Level Book 1
Classwork
1. Write the electronic configuration of 24Cr and
29Cu.
2. Write the electronic configuration of Fe, Fe2+
and Fe3+. Explain why Fe2+ can be easily
oxidized to Fe3+.
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.109)
24Cr
[Ar]
3d
4s
Halfly-filled subshell  extra stability
29Cu
[Ar]
3d
4s
Fully-filled subshell  extra stability
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
Atomic size of elements
…..
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 123)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 123)
Q: Explain why the atomic radius increases down a group.
• Moving down a group, an atom would have one
more electron shell occupied which lies at a
greater distance from the nucleus.
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 123)
Remarks:
Effective nuclear charge can only be applied to
make comparison between atoms in the same
period.
Never apply effective nuclear charge to atoms in
the same group.
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The END
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New Way Chemistry for Hong Kong A-Level Book 1