Atomic Radius, Ionisation Energy and Electronegativity
Across a period the effective nuclear charge rises so radius falls while ionisation energy and electronegativity rise; down a group the opposite holds.
What is Atomic Radius, Ionisation Energy and Electronegativity?
Across a period the effective nuclear charge rises so radius falls while ionisation energy and electronegativity rise; down a group the opposite holds.
Key formula / rule: Effective nuclear charge increases across a period.
Key points
- Compare periodic trends across periods and down groups.
- Analyse anomalies in ionisation energy trends.
Common exam trap
Reading trends without accounting for shielding.
Definitions
- Term
Atomic Radius, Ionisation Energy and Electronegativity
- Meaning
Across a period the effective nuclear charge rises so radius falls while ionisation energy and electronegativity rise; down a group the opposite holds.
- Term
Atomic Radius, Ionisation Energy and Electronegativity — explanation
- Meaning
Every trend traces back to the competition between nuclear attraction and shielding. Anomalies at nitrogen and oxygen come from half-filled subshell stability and electron pairing repulsion.
Learning objectives
Compare periodic trends across periods and down groups.
Analyse anomalies in ionisation energy trends.
Formulae
- Key point
Effective nuclear charge increases across a period.
- Key point
Ionisation energy shows a dip from group 15 to group 16.
- Key point
Cations are smaller and anions larger than the parent atoms.
Prerequisites
CHE-U2-PT-T1-S1-C1
Common mistakes
Reading trends without accounting for shielding.
Ignoring the half-filled stability anomaly in ionisation energy.
Keywords
Atomic
Radius
Ionisation
Energy
Practice preview
Arrange the following elements in increasing order of their atomic radii: Na, Mg, Al, Si.…
medium
Which of the following correctly describes the trend of atomic radius across a period in the modern periodic table?…
easy
How does the first ionisation energy generally change as we move down a group in the modern periodic table?…
easy