Asked by john
ionic radius
anion
cation
valence electron
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Here are concise definitions and key points for each term, with examples and important trends.
- Ionic radius
- Definition: The effective radius of an ion in a crystal lattice — a measure of how large the ion is when it has gained or lost electrons. Usually reported in picometres (pm) or ångströms (Å; 1 Å = 100 pm).
- Notes: Not a single fixed value — depends on coordination number (how many neighbors), oxidation state, and measurement/definition method.
- Trend/example: Anions are larger than their neutral atoms; cations are smaller. In an isoelectronic series (same electron count), ionic radius decreases with increasing nuclear charge (higher positive charge).
- Anion
- Definition: An ion with a net negative charge (has gained one or more electrons).
- Example: Cl− (chloride), O2− (oxide), S2− (sulfide).
- Properties: Larger than the parent neutral atom because added electrons increase electron–electron repulsion and expand the electron cloud.
- Cation
- Definition: An ion with a net positive charge (has lost one or more electrons).
- Example: Na+ (sodium ion), Ca2+ (calcium ion), Fe3+ (ferric).
- Properties: Smaller than the parent neutral atom because loss of electrons reduces electron–electron repulsion and often removes an entire shell.
- Valence electron
- Definition: An electron in the outermost shell (highest principal quantum number) of an atom; these electrons participate in chemical bonding and determine chemical reactivity.
- Example: Oxygen has 6 valence electrons (2s2 2p4); sodium has 1 valence electron (3s1).
- Role: Loss or gain of valence electrons forms cations or anions; having a full valence shell (often an octet for main-group elements) is a major driving force for ion formation.
Quick illustrative points:
- Na (neutral) → Na+: loses its one valence electron, becomes smaller.
- Cl (neutral) → Cl−: gains one valence electron, becomes larger.
- Isoelectronic series example: O2− > F− > Na+ > Mg2+ in ionic radius (largest to smallest), because they all have 10 electrons but increasing nuclear charge pulls electrons in tighter.
If you want, I can give numeric ionic radii for specific ions, a periodic trend chart, or visual diagrams. Which would help you most?
- Ionic radius
- Definition: The effective radius of an ion in a crystal lattice — a measure of how large the ion is when it has gained or lost electrons. Usually reported in picometres (pm) or ångströms (Å; 1 Å = 100 pm).
- Notes: Not a single fixed value — depends on coordination number (how many neighbors), oxidation state, and measurement/definition method.
- Trend/example: Anions are larger than their neutral atoms; cations are smaller. In an isoelectronic series (same electron count), ionic radius decreases with increasing nuclear charge (higher positive charge).
- Anion
- Definition: An ion with a net negative charge (has gained one or more electrons).
- Example: Cl− (chloride), O2− (oxide), S2− (sulfide).
- Properties: Larger than the parent neutral atom because added electrons increase electron–electron repulsion and expand the electron cloud.
- Cation
- Definition: An ion with a net positive charge (has lost one or more electrons).
- Example: Na+ (sodium ion), Ca2+ (calcium ion), Fe3+ (ferric).
- Properties: Smaller than the parent neutral atom because loss of electrons reduces electron–electron repulsion and often removes an entire shell.
- Valence electron
- Definition: An electron in the outermost shell (highest principal quantum number) of an atom; these electrons participate in chemical bonding and determine chemical reactivity.
- Example: Oxygen has 6 valence electrons (2s2 2p4); sodium has 1 valence electron (3s1).
- Role: Loss or gain of valence electrons forms cations or anions; having a full valence shell (often an octet for main-group elements) is a major driving force for ion formation.
Quick illustrative points:
- Na (neutral) → Na+: loses its one valence electron, becomes smaller.
- Cl (neutral) → Cl−: gains one valence electron, becomes larger.
- Isoelectronic series example: O2− > F− > Na+ > Mg2+ in ionic radius (largest to smallest), because they all have 10 electrons but increasing nuclear charge pulls electrons in tighter.
If you want, I can give numeric ionic radii for specific ions, a periodic trend chart, or visual diagrams. Which would help you most?
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