STPM Chemistry Form 6 Notes – Terminology and Concepts: The Periodic Table (Part 5 – Final)

by BerryBerryTeacher

in Berry Reference (Notes)

The long awaited fitting end to the notes on the chapter of “Periodic Table for STPM Form 6 Chemistry” from Berry Berry Easy is finally here.  You would have learnt about the history of the periodic table (typically not examined but it’ll be good to know for your general knowledge) in Part 1, the general constituent of the modern periodic table (short and long periods) in Part 2, the atomic and ionic radii of a element in a periodic table in Part 3, physical phyiscal, electrical properties and ionisation energy in Part 4. So to wrap things up, you’ll learn in Part 5 (Finale) regarding the electronegativity, electron affinity and variation of period of d-block elements.

Despite being the last subtopic in this chapter, it is no less important than those from Part 2-4. So make sure you know everything in this whole series of notes before you declare yourself examination ready regarding the periodic table. (Just remember not to ‘look down’ on the periodic table and brush it off as easy as if you’re in Form 4/5. This is more in-depth than what you have learnt previously)

STPM Chemistry Form 6 Notes – Terminology and Concepts: The Periodic Table (Part 5 – Final)

A) Electronegativity

Electronegativity – measure how easy it is for an atom to gain electrons and how much an atom will pull electrons away from other atoms it has bonded to / covalent bond (similar to electron affinity but the difference is electron affinity deals with isolated atoms in the gas phase).

Across the periodic table (left to right)

  1. Electronegativity increases.
  2. Left side: prefer to lose electrons.
  3. Right side: prefer to gain electrons.
  4. Noble gases: no electron affinity.

Down the periodic table

  1. Electronegativity decreases.
  2. It is because the shielding effect (nuclear charge increases but screening effect increase and the atomic size increases and as a result, the effective charge decrease).

B) Electron Affinity

Electron affinity – the energy change that occurs when a gaseous atom picks up an extra electron.

First electron affinity is exothermic:
Example: O (g) + e –> O- (g)
First electron is pulled/attracted by the positively charged oxygen atom nucleus.

Second electron affinity is endothermic:
Example: O- (g) + e –> O2- (g)
Second electron is repelled by the existing negative charge on the oxygen ion.

Across the periodic table (left to right)

  1. Left: elements want to lose electrons to be the nearest noble gas. As result, not much energy is released when these elements gain an extra electron. Electron affinity to be slightly negative.
  2. Right: elements want to gain electrons to be the nearest noble gas. As result, a very high energy to be released. Electron affinity to be more negative.

Down the periodic table

  1. Elements want to gain electron less (shielding effect)
  2. Bottom: elements have less negative electron affinities.

C) Variation of the Period of d-block Element

Across the periodic table – First series (left to right)

  1. Atomic size is approximately the same (except Sc and Ti).
  2. Effective nuclear charge remains almost.
  3. High melting points and boiling points (except Zn).
  4. Density increases (but decreases for zinc).
  5. 1st and 2nd ionisation energies of the elements increase slightly (as the proton numbers increase)
  6. 3rd and 4th ionisation energies of the elements increase drastically.

Please revise previous parts in this series of notes if you want to understand the complete idea (for STPM level) on the periodic table.

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