Periodicity
Explain trends in covalent radius, first ionisation energy and electronegativity, and connect electron arrangement to bonding and structure.
How to study Higher Chemistry
Move deliberately between structure, equations, quantitative models, unfamiliar evidence and justified experimental conclusions, while using current official materials for exact paper and assignment practice.
Core concepts
Concept 1
Covalent radius generally decreases across a period and increases down a group as nuclear attraction and occupied shells change.
Exam cue: State the trend, then explain it using nuclear charge, shielding and distance from the nucleus.
Concept 2
First ionisation energy and electronegativity generally increase across a period and decrease down a group.
Exam cue: Distinguish energy needed to remove an electron from attraction for a bonding pair of electrons.
Concept 3
Electron arrangements help explain bonding and structure for elements in the first 20 positions of the periodic table.
Exam cue: Use the element’s position and electron arrangement before predicting its bonding and structure.
Risk pitfalls and guardrails
Explaining every trend only by saying that atoms become larger or smaller.
Guardrail: Check structures, formulae, charges, equation balance, units, signs and experimental conditions before committing to the final conclusion.
Confusing first ionisation energy with electronegativity.
Guardrail: Check structures, formulae, charges, equation balance, units, signs and experimental conditions before committing to the final conclusion.
Treating periodic trends as exception-free numerical rules.
Guardrail: Check structures, formulae, charges, equation balance, units, signs and experimental conditions before committing to the final conclusion.
Memory anchors
Across a period: radius
Covalent radius generally decreases as nuclear charge increases without adding a new occupied shell.
Down a group: radius
Covalent radius generally increases because additional occupied electron shells are present.
First ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms.
Electronegativity
The attraction an atom has for the shared pair of electrons in a covalent bond.
Across a period: attraction
First ionisation energy and electronegativity generally increase across a period.
Down a group: attraction
Shielding and distance increase, so first ionisation energy and electronegativity generally decrease.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Why does covalent radius generally decrease from sodium to chlorine across period 3?
Which change generally occurs on descending group 1 from lithium to potassium?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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