Periodic Trends: Atomic & Ionic Radii 301 Chemistry
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Atomic Radii Measured by halving the distance between two nuclei in a bond.
Decreases across the period Atomic Radii Trends Decreases across the period Increases down a group
Decreases across a period The number of protons increases and electrons are in the same energy level This increases the electrostatic attractions and the electrons are pulled in closer to the nucleus Decreasing the radius of the atom
Increases down a group The atoms in the group have more electron shells, therefore the valence electrons are further from the nucleus The valence electrons are ‘shielded’ from the positive nucleus by the inner electron shells, so the electrostatic attraction between the electrons and nucleus is decreased.
Ionic Radii - Cations
Ionic Radii - Cations Cations are always smaller than their corresponding atoms There are less electron shells so the valence electrons are closer to the nucleus.
Ionic Radii - Anions
Ionic Radii - Anions Negative anions are always larger than their parent atoms There are more electrons in the valence shell – there is more electron-electron repulsion increasing the radii