Name: how ionic charge changes ion size
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 10 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.2.2

Ionic Radii

Ein Ionenradius ist der Radius eines Kations oder eines Anions, definiert durch den Abstand zwischen den Ionen in einer ionischen Verbindung. Kationen sind kleiner als das übergeordnete Atom, während Anionen größer sind. Ähnlich wie Atomradien, werden Ionenradien durch die Anzahl der Elektronen, die Orbitale die seine Valenzelektronen halten, und die nukleare Ladung bestimmt.Denken Sie an Lithium, dass eine Elektronenkonfiguration aus einem Heliumkern und einem äußerstem 2s Elektron hat. Das 2s Elektron ist von der Kernladung durch zwei 1s-Elektronen abgeschirmt und trägt dem Atomradius von 152 Pikometern bei. Der Verlust des äußersten 2s Elektrons erzeugt ein Lithium-Kation, das weniger Elektronen aber die gleiche Anzahl von Protonen wie das Lithiumatom hat.Die beiden 1s Elektronen werden näher am Kern gehalten, weil sie eine größere effektive Kernladung als das 2s Elektron haben. Somit beträgt der Ionenradius des Lithiumkations 60 Picometer und ist damit viel kleiner als das Lithiumatom. Dieser Trend ist im Allgemeinen bei allen Metallkationen und ihren Elternatomen zu beobachten.Im Gegensatz dazu sind Anionen größer als ihre Mutteratome. Wenn ein Fluoratom ein Elektron aufnimmt, bekommt es ein zusätzliches äußerstes Elektron, aber die Anzahl der Protonen, und damit die Kernladung, bleibt gleich. Die verstärkte Elektron-Elektron-Abstoßung bewirkt, dass die Elektronen sich mehr im Raum auszubreiten.Das Fluorid-Anion hat also einen Radius von 136 Picometern, was viel größer als das Mutteratom ist. Im Allgemeinen steigt der Ionenradius für s-und p-Blockelemente in der Spalte nach unten, da die Zahl der Hauptenergieebenen, und damit die Anzahl der Orbitale, steigt. Was ist mit einer Gruppe von Atomen und Ionen, die die gleiche Anzahl von Elektronen haben?Sie werden als isoelektronische Reihe bezeichnet und können nach steigender Ordnungszahl angeordnet werden. Jedes Mitglied der abgebildeten isoelektronischen Serie hat 18 Elektronen. Sie unterscheiden sich jedoch in der Anzahl der Protonen.Das Sulfid-Ion hat 16 Protonen, die 18 Elektronen anziehen, während das Calcium-Ion 20 Protonen und die gleiche Anzahl von Elektronen anzieht. So kann Calcium mit mehr Protonen die Elektronen viel näher zum Kern ziehen als Sulfid, wodurch das Calcium-Ion kleiner als das Sulfid-Ion wird. Je größer die nukleare Ladung, desto kleiner der Radius, obwohl das Hinzufügen einer Elektronenschale diesen Trend unterbricht.Dennoch ist Sulfid das größte und Calcium das kleinste Ion in dieser Reihe.

ionenradien

Der Ionenradius ist das Maß zur Beschreibung der Größe eines Ions. Ein Kation hat immer weniger Elektronen und die gleiche Anzahl Protonen wie das Ursprungsatom; es ist somit kleiner als das Atom, von dem es sich ableitet. Beispielsweise beträgt der kovalente Radius eines Aluminiumatoms (1s22s22p63s23p1) 118 pm, während der Ionenradius eines Al3+ (1s22s22p6) 68 pm beträgt. Wenn Elektronen aus der äußeren Valenzschale entfernt werden, erfahren die verbleibenden Kernelektronen, welche die kleinere Schalen besetzen, eine größere effektive Kernladung Zeff und werden noch näher an den Kern herangezogen. Kationen mit größeren Ladungen sind kleiner als Kationen mit kleineren Ladungen (z. B. hat V2+ einen Ionenradius von 79 pm, während der von V3+ 64 pm beträgt). Entlang der Gruppen des Periodensystems nach unten gehend weisen Kationen aufeinanderfolgender Elemente mit derselben Ladung im Allgemeinen größere Radien auf, was einem Anstieg der Hauptquantenzahl n entspricht. Ein Anion (negatives Ion) entsteht durch die Addition eines oder mehrerer Elektronen in die Valenzschale eines Atoms. Dies führt zu einer stärkeren Abstoßung zwischen den Elektronen und einer Verringerung von Zeff pro Elektron. Beide Effekte (die erhöhte Anzahl an Elektronen und die verringerte Zeff) führen dazu, dass der Radius eines Anions größer ist als der des ursprünglichen Atoms. Beispielsweise hat ein Schwefelatom ([Ne]3s23p4) einen kovalenten Radius von 104 pm, während der Ionenradius des Sulfidanions ([Ne]3s23p6) 170 pm beträgt. Für aufeinanderfolgende Elemente in einer beliebigen Gruppe haben Anionen größere Hauptquantenzahlen und damit auch größere Radien. Atome und Ionen mit gleicher Elektronenkonfiguration werden als isoelektronisch bezeichnet. Beispiele für isoelektronische Spezies sind N3–, O2–, F–, Ne, Na+, Mg2+, und Al3+ (1s22s22p6). Eine weitere isoelektronische Reihe ist P3–, S2–, Cl–, Ar, K+, Ca2+ und Sc3+ ([Ne]3s23p6). Bei isoelektronischen Atomen oder Ionen bestimmt die Anzahl der Protonen die Größe. Je größer die Kernladung, desto kleiner ist der Radius in einer Reihe isoelektronischer Ionen und Atome. Dieser Text wurde adaptiert von <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">OpenStax Chemistry 2e, Section 6.5: Periodic Variations in Element Properties.</a>

Ionenradien

Der Ionenradius ist das Maß, das verwendet wird, um die Größe eines Ions zu beschreiben. Ein Kation hat immer weniger Elektronen und die gleiche Anzahl an Protonen wie das Mutteratom; es...

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how ionic charge changes ion size

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from.

Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull draws them closer to the nucleus.

Cations with larger charges are usually smaller than cations with smaller charges. For example, V2+ has an ionic radius of 79 pm, while V3+ is smaller at 64 pm. Moving down a group in the periodic table, cations with the same charge generally get larger. This happens because the principal quantum number, n, increases.

Anions are negative ions formed when one or more electrons are added to the valence shell. Extra electrons increase electron repulsion and reduce Zeff per electron. Both effects make an anion larger than its parent atom. Sulfur is an example: a sulfur atom has a covalent radius of 104 pm, while the sulfide anion has an ionic radius of 170 pm. Anions also tend to have larger radii down a group because n increases.

Atoms and ions with the same electron configuration are called isoelectronic. One example set is N3−, O2−, F−, Ne, Na+, Mg2+, and Al3+, which all have the same electron arrangement. Another is P3−, S2−, Cl−, Ar, K+, Ca2+, and Sc3+. In an isoelectronic series, the number of protons controls size. The greater the nuclear charge, the smaller the radius.

How Ionic Charge Changes Ion Size

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ionic radii

Ionic radius describes the size of an ion. It changes when an atom gains or loses electrons. Cations are positive ions with fewer electrons than the parent atom, and they are smaller than the atoms they come from. Aluminum shows this pattern clearly. A neutral aluminum atom has a covalent radius of 118 pm, while Al3+ has an ionic radius of 68 pm. When electrons are removed from the outer valence shell, the remaining core electrons feel a stronger effective nuclear charge, or Zeff. That pull...

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Learn how cations and anions change size, why ionic radius varies with charge, and how isoelectronic species compare across the periodic table.

How Ionic Charge Changes Ion Size | JoVE K12

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How Ionic Charge Changes Ion Size

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