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LearnEdexcelYCH112018 specificationWCH11 · Unit 1: Structure, Bonding and Introduction to Organic ChemistryAtomic structure and the Periodic Table

WCH11 · Module

Atomic structure and the Periodic Table

3 subtopics≈ 130 min in total

Start the module: Period 3 trends and oxides Open graphing calculator

Period 3 trends and oxides
Across period 3 atomic radius decreases (more protons, same shielding). Melting points rise from Na to Si (metallic bonding strengthens, then giant covalent Si), then fall sharply to simple molecular P₄, S₈, Cl₂ and atomic Ar. Conductivity is high for metals, low for Si (semiconductor), negligible after. Oxides go from basic ionic ( $\mathrm{Na_2O}$ , MgO) through amphoteric ( $\mathrm{Al_2O_3}$ ) and giant covalent ( $\mathrm{SiO_2}$ , acidic) to acidic simple molecular ( $\mathrm{P_4O_{10}}$ , $\mathrm{SO_2}$ , $\mathrm{SO_3}$ ). Chlorides go from ionic (NaCl dissolves, pH 7) to covalent ones that hydrolyse to acidic solutions ( $\mathrm{SiCl_4}$ , $\mathrm{PCl_5}$ ).
≈ 45 min
Particles, isotopes and orbitals
Electrons occupy shells ( $n=1,2,3…$ ) divided into subshells (s, p, d), each made of orbitals holding at most two electrons of opposite spin. Subshells fill in order of energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. Exceptions: Cr is [Ar] 3d⁵ 4s¹ and Cu is [Ar] 3d¹⁰ 4s¹. Transition-metal ions lose 4s electrons first. Relative atomic mass is the weighted mean from a mass spectrum: $A_r=\frac{\sum(m/z\times\text{abundance})}{\sum\text{abundance}}$ .
≈ 45 min
Ionisation energies
The first ionisation energy is the energy needed to remove one mole of electrons from one mole of gaseous atoms: $\mathrm{X(g)\rightarrow X^+(g)+e^-}$ . It depends on nuclear charge, distance of the outer electron from the nucleus and shielding. Across a period it generally increases (more protons, similar shielding); down a group it decreases (further away, more shielding). Dips occur at Group 13 (new p subshell, higher energy) and Group 16 (spin-pair repulsion). Successive ionisation energies show big jumps when an inner shell is broken into.
≈ 40 min