Name: how ionic charge changes ion size
Uploaded: 2020-09-03T13:38:28.000Z
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North Carolina K-12 Science Standard Course of Study

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Chemistry

Matter and its Interactions

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Ionic Radii

Un rayon ionique est le rayon d'un cation ou un anion définie par la distance entre les ions dans un composé ionique. Les cations sont plus petits que l'atome parent, tandis que les anions sont plus grands. Semblable aux rayons atomiques, les rayons ioniques sont déterminés par le nombre d'électrons, les orbitales tenant ses électrons de valence et la charge nucléaire.Envisager de lithium, qui a une configuration électronique d'un noyau d'hélium et un ultrapériphériques 2s électron. L'électron 2s est protégé de la charge nucléaire par deux électrons 1s et contribue au rayon atomique de 152 picomètres. La perte de l'électron 2S le plus externe génère un cation lithium, qui a moins d'électrons mais le même nombre de protons que l'atome parent.Les deux électrons 1s sont maintenus plus près du noyau parce qu'ils subissent une charge nucléaire efficace plus grande que l'électron 2s. Ainsi, le rayon ionique du cation lithium est de 60 picomètres, ce qui est beaucoup plus petit que l'atome parent. Cette tendance est généralement observée avec tous les cations métalliques et leurs atomes parents.En revanche, les anions sont plus grands que leurs atomes parents. Quand un atome de fluor accepte un électron, il y a un électron externe supplémentaire, mais le nombre de protons, et donc la charge nucléaire, reste le même. L'augmentation de l'électron-répulsion électron fait que les électrons s'étalent davantage dans l'espace.Ainsi, l'anion fluoré a un rayon de 136 picomètres, ce qui est beaucoup plus grand que l'atome parent. En général, le rayon ionique pour les éléments du bloc s et p augmente en bas de la colonne, alors que le nombre de niveaux d'énergie principaux, et donc le nombre d'orbitales, augmente. Que penser d'un groupe d'atomes et d'ions qui ont le même nombre d'électrons Ils sont appelés une série isoélectronique et peuvent être organisés en augmentant le nombre atomique.Chaque membre de la série isoélectronique représentée a 18 électrons. Cependant, ils diffèrent par le nombre de protons. L'ion sulfure a 16 protons attirant 18 électrons, tandis que l'ion calcium a 20 protons attirant le même nombre d'électrons.Ainsi, avec plus de protons, le calcium peut tirer des électrons beaucoup plus près du noyau que le sulfure, ce qui fait que l'ion calcium est plus petit que l'ion sulfure. Plus la charge nucléaire est grande, plus le rayon est petit, bien que l'ajout d'une enveloppe d'électrons perturbe cette tendance. Néanmoins, le sulfure est le plus grand et le calcium est le plus petit ion de cette série.

rayons ioniques

Le rayon ionique est la mesure utilisée pour décrire la taille d'un ion. Un cation a toujours moins d'électrons et le même nombre de protons que l'atome parent ; il est plus petit que l'atome à partir duquel il est obtenu. Par exemple, le rayon covalent d'un atome d'aluminium (1s22s22p63s23p1) est de 118 pm, alors que le rayon ionique d'un Al3+ (1s22s22p6) est de 68 pm. Comme les électrons sont retirés de la couche de valence externe, les électrons de cœur restants qui occupent des plus petites couches subissent une charge nucléaire effective plus importante Zeff et sont attirés encore plus près du noyau. 
 
 Les cations avec des charges plus importantes sont plus petits que les cations avec des charges plus faibles (par exemple, V2+ a un rayon ionique de 79 pm, alors que celui de V3+ est de 64 pm). En descendant dans les groupes du tableau périodique, les cations d'éléments successifs ayant la même charge ont généralement des rayons plus grands, ce qui correspond à une augmentation du nombre quantique principal, n.
 
 Un anion (ion négatif) est formé par l'addition d'un ou de plusieurs électrons sur la couche de valence d'un atome. Cela entraîne une répulsion plus importante entre les électrons et une diminution du Zeff par électron. À cause des deux effets (l'augmentation du nombre d'électrons et la diminution du Zeff), le rayon d'un anion est plus grand que celui de l'atome parent. Par exemple, un atome de soufre ([Ne]3s23p4) a un rayon covalent de 104 pm, alors que le rayon ionique de l'anion sulfure ([Ne]3s23p6) est de 170 pm. Pour les éléments consécutifs en descendant dans n'importe quel groupe, les anions ont des nombres quantiques principaux plus grands et, par conséquent, des rayons plus grands. 
 
 On dit que les atomes et les ions qui ont la même configuration électronique sont isoélectroniques. Les espèces isoélectroniques sont N3–, O2–, F–, Ne, Na+, Mg2+ et Al3+ (1s22s22p6). Une autre série isoélectronique est P3–, S2–, Cl–, Ar, K+, Ca2+ et Sc3+ ([Ne]3s23p6). Pour les atomes ou les ions qui sont isoélectroniques, le nombre de protons détermine la taille. Plus la charge nucléaire est importante, plus le rayon d'une série d'ions et d'atomes isoélectroniques est petit. 
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/6-5-periodic-variations-in-element-properties">OpenStax Chemistry 2e, Section 6.5 : Variations périodiques dans les propriétés des éléments.</a>

Rayons ioniques

Le rayon ionique est la mesure utilisée pour décrire la taille d’un ion. Un cation a toujours moins d’électrons et le même nombre de protons que l’atome parent ; il...

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Periodic Properties of the Elements

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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.

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How Ionic Charge Changes Ion Size

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