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1.5Unit 1. Structure, Bonding and Introduction to Organic Chemistry

The Periodic Table — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

5 min read 9 parts Lesson 6 of 36 1 quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Lesson summary

1.5 The Periodic Table — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Explain trends in ionisation energy and in the melting points of the elements across period 3.Periodic Table arrangement — elements are in order of increasing atomic number, in groups (columns) and periods (rows).Peri…

  • Periodicity
  • Ionisation energy trend
  • General increase across a period
  • Beryllium to boron
  • Nitrogen to oxygen
  • Magnesium to aluminium

Part 1 of 7Periodicity and ionisation energy across a period

1Periodic Table arrangement
  • Periodic Table arrangement elements are in order of increasing atomic number, in groups (columns) and periods (rows).
2Periodicity
  • Periodicity repeating patterns in chemical and physical properties across periods.
3Ionisation energy trend
  • IE1 is low for Group 1 metals and very high for noble gases.
4General increase across a period
  • General increase across a period nuclear charge increases while electrons are added to the same shell.
  • The atomic radius decreases as the outer shell is pulled closer to the nucleus.
  • Shielding by inner shells stays roughly constant.
  • The outer electron is harder to remove, so ionisation energy rises.

Part 2 of 7Dips in first ionisation energy in period 2

1
Beryllium to boron
  • IE1 falls from 900 to 800 kJ mol-1.
  • Boron's outer electron is in the 2p subshell (1s2 2s2 2px1), which is higher in energy than 2s.
  • It is also shielded by the 2s electrons, so less energy is needed to remove it.
2
Nitrogen to oxygen
  • IE1 falls from 1400 to 1310 kJ mol-1.
  • Oxygen (2px2 2py1 2pz1) has two electrons in one 2p orbital.
  • Spin-pair repulsion between them makes one easier to remove.
  • Nitrogen has one electron in each 2p orbital (2px1 2py1 2pz1).

Part 3 of 7Dips in first ionisation energy in period 3

1Magnesium to aluminium
  • IE1 falls from 738 to 578 kJ mol-1.
  • Aluminium's thirteenth electron is in the 3p subshell, higher in energy than 3s.
  • It is shielded by the 3s electrons, so it is easier to remove.
2Phosphorus to sulfur
  • IE1 falls from 1012 to 1000 kJ mol-1.
  • Sulfur has two electrons in the 3px orbital.
  • Spin-pair repulsion makes one of them easier to remove.
  • Phosphorus has one electron in each 3p orbital.

Part 4 of 7Ionisation energy down a group

Ionisation energy down a group
Trend
  • Trend ionisation energy decreases down a group.
Factors
  • Nuclear charge increases because there are more protons.
  • Atomic radius increases because extra shells are added, so the outer electron is further from the nucleus.
  • Shielding by inner shells increases.
Conclusion
  • Conclusion the extra distance and shielding outweigh the increased nuclear charge, so the outer electron is easier to remove.

Part 5 of 7Melting points across period 3: overview

Pattern
  • Pattern melting point rises from sodium to a maximum at silicon, then falls sharply from phosphorus to argon.
Explanation
  • Explanation the trend depends on the bonding and structure of each element.
ElementsStructure and bondingMelting point
Na, Mg, Algiant metallic latticeincreases Na < Mg < Al
Sigiant covalent (macromolecular)highest
P, S, Cl, Arsimple molecules (P4, S8, Cl2, Ar atoms)low, with S higher than P

Part 6 of 7Metallic elements: sodium, magnesium and aluminium

Metallic elements: sodium, magnesium and aluminium
Structure
  • Structure positive ions in a giant lattice held by a sea of delocalised electrons.
  • Na donates one electron, Mg two and Al three to the sea.
Bond strength
  • Bond strength the attraction between a 3+ ion and more delocalised electrons is much larger than between a 1+ ion and fewer electrons.
  • Metallic bonding is stronger in Al than in Na, so melting points rise from Na to Al.
Drawing the lattice
  • Drawing the lattice metals are solid at room temperature (except mercury), so show a regular arrangement of close-packed positive ions.
  • Do not draw large gaps or a random arrangement, which looks like a liquid.
  • The delocalised electrons need not be shown individually.

Part 7 of 7Silicon and the non-metals

Silicon and the non-metals
Silicon
  • Silicon has the highest melting point because each atom is bonded to its neighbours by strong covalent bonds in a giant molecular structure.
Non-metals P, S, Cl and Ar
  • Non-metals P, S, Cl and Ar exist as simple molecules or single atoms.
  • Covalent bonds within molecules are strong.
  • Only weak instantaneous dipole-induced dipole forces act between molecules.
  • Little energy is needed to overcome them, so melting points are low.
Sulfur versus phosphorus
  • Sulfur versus phosphorus sulfur has a higher melting point because larger S8 molecules have stronger intermolecular forces than P4.

Key terms

TermMeaning
PeriodicityThe repeating pattern of properties of elements across periods.
ShieldingThe reduction in attraction of the nucleus on outer electrons by inner electrons.
Spin-pair repulsionRepulsion between two electrons paired in the same orbital.
Giant covalent structureA lattice of atoms held by a network of strong covalent bonds.
Instantaneous dipole-induced dipole forcesWeak forces between simple molecules caused by temporary dipoles.
Delocalised electronsOuter electrons free to move throughout a metal lattice.

Avoid these mistakes

1
Explaining the dip between Be and B by spin-pair repulsion — it is due to the higher energy and shielding of the 2p electron.
2
Explaining the dip between N and O by shielding — it is due to spin-pair repulsion in the paired 2p orbital.
3
Saying melting a simple molecular element breaks covalent bonds — only weak intermolecular forces are overcome.
4
Drawing a metal lattice with gaps or a random arrangement.

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