9701 · 1.1
Particles in the atom and atomic radius flashcards
Revision flashcards for Cambridge 9701 Particles in the atom and atomic radius (syllabus 1.1). Flip, recall, then mark a real past-paper question.
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What are the relative mass and relative charge of a proton?
Relative mass: 1. Relative charge: +1.
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What are the relative mass and relative charge of a neutron?
Relative mass: 1. Relative charge: 0.
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What are the relative mass and relative charge of an electron?
Relative mass: 1/1840 (often considered negligible). Relative charge: -1.
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Define Atomic Number (Z).
The number of protons in the nucleus of an atom. It defines the element.
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Define Mass Number (A).
The total number of protons and neutrons in the nucleus of an atom.
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Define isotopes.
Atoms of the same element (same number of protons) but with different numbers of neutrons (and thus different mass numbers).
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Why does atomic radius decrease across a period?
Nuclear charge increases, but shielding remains similar as electrons are added to the same principal shell. This causes a stronger attraction on the outer electrons, pulling them closer to the nucleus.
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Why does atomic radius increase down a group?
The number of principal electron shells increases. The increased shielding from inner shells outweighs the effect of the increased nuclear charge, so the outer electrons are further from the nucleus.
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Why is a positive ion (cation) smaller than its parent atom?
The ion has lost its outer shell of electrons, and/or there is less electron-electron repulsion among the remaining electrons, which are pulled more tightly by the unchanged nuclear charge.
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Why is a negative ion (anion) larger than its parent atom?
An extra electron has been added, increasing electron-electron repulsion. The electrons are pushed further apart, and the unchanged nuclear charge cannot hold them as tightly.
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What does the term 'isoelectronic' mean?
Used to describe different species (atoms or ions) that have the same number of electrons and the same electron configuration. For example, $O^{2-}$, $F^{-}$, $Ne$, and $Na^{+}$ are all isoelectronic.