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periodic table trends
A LevelChemistry~4 min read
Overview
This lesson explores the fundamental trends observed across the Periodic Table, focusing on how atomic structure influences the physical and chemical properties of elements. Understanding these trends is crucial for predicting reactivity and explaining the behaviour of different groups and periods.
Atomic Radius Trends
Atomic radius generally **decreases across a period** and **increases down a group**. * **Across a period (left to right):** The number of protons (nuclear charge) increases, pulling the outer electrons closer to the nucleus. While the number of electron shells remains the same, the increased ef...
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Key Concepts
- Atomic Radius: Half the distance between the nuclei of two identical atoms bonded together.
- Ionisation Energy: The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
- Electron Affinity: The energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous 1- ions.
- Electronegativity: The power of an atom to attract the electron density in a covalent bond towards itself.
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Exam Tips
- →Always refer to 'effective nuclear charge' and 'shielding effect' when explaining trends, especially for ionisation energy and atomic radius.
- →Be precise with definitions: distinguish between 'energy required to remove' (ionisation energy) and 'energy change when adding' (electron affinity).
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