2. New Way Chemistry for Hong Kong A-Level Book 1 1 Chapter 5 Electronic Configurations and the Periodic Table

3. New Way Chemistry for Hong Kong A-Level Book 1 2 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.

4. New Way Chemistry for Hong Kong A-Level Book 1 3 Evidence of Sub-shells 4.2 Deduction of Electronic Structure from Ionization Enthalpies (p.93)

5. New Way Chemistry for Hong Kong A-Level Book 1 4 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.

6. New Way Chemistry for Hong Kong A-Level Book 1 5 Classwork 1.Write the electronic configuration of 24 Cr and 29 Cu. 2.Write the electronic configuration of Fe, Fe 2+ and Fe 3+. Explain why Fe 2+ can be easily oxidized to Fe 3+.

7. New Way Chemistry for Hong Kong A-Level Book 1 6 24 Cr 3d4s [Ar] 3d4s [Ar] 29 Cu Halfly-filled subshell  extra stability Fully-filled subshell  extra stability 5.1 Relative Energies of Orbitals (SB p.109)

8. New Way Chemistry for Hong Kong A-Level Book 1 7 Atomic size of elements 5.6 Atomic Size of Elements (p. 128) …..

9. New Way Chemistry for Hong Kong A-Level Book 1 8 5.6 Atomic Size of Elements (p. 123)

10. New Way Chemistry for Hong Kong A-Level Book 1 9 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. 5.6 Atomic Size of Elements (p. 123)

11. New Way Chemistry for Hong Kong A-Level Book 1 10 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. Remarks: 5.6 Atomic Size of Elements (p. 123)

12. New Way Chemistry for Hong Kong A-Level Book 1 11 The END