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

Um raio iônico é o raio de um cátion ou de um ânion definido pela distância entre os íons num composto iônico. Os catíons são mais pequenos do que o átomo principal, enquanto que os aníons são maiores. Semelhante aos raios atómicos, os raios iônicos são determinados pelo número de elétrons, os orbitais com os seus elétrons de valência, e a carga nuclear.Consideremos o lítio, que tem uma configuração de elétrons de um núcleo de hélio e um elétron de 2s mais exterior. O elétron 2s está protegido da carga nuclear por dois elétrons de 1s e contribui para o raio atómico de 152 picometros. A perda do elétron dos 2s mais periféricos gera um cátion de lítio, que tem menos elétrons mas o mesmo número de prótons que o átomo principal.Os dois elétrons de 1s são mantidos mais próximos do núcleo porque experimentam uma maior carga nuclear efetiva do que a carga nuclear dos 2s elétrons. Assim, o raio iônico do cátion de lítio é de 60 picometros, que é muito menor do que o átomo principal. Esta tendência é geralmente observada em todos os catíons metálicos e os seus átomos principais.Em contraste, os aníons são maiores do que os seus átomos principais. Quando um átomo de flúor aceita um elétron, há um elétron adicional mais exterior, mas o número de prótons, e consequentemente a carga nuclear, permanecem iguais. O aumento dos elétrons a repulsa de elétrons leva a que estes se espalharem mais no espaço.Assim, o ânion de flúor tem um raio de 136 picometros, que é muito maior do que o átomo principal. Em geral, o raio iônico para os elementos do bloco s e p aumenta na coluna, à medida que o número dos níveis principais de energia, e consequentemente o número de orbitais, aumenta. E um grupo de átomos e íons que têm o mesmo número de elétrons, são referidos como uma série isoelétrica e podem ser organizados através do aumento do número atómico.Cada membro da série isoelétrica retratada tem 18 elétrons. No entanto, diferem no número de prótons. O íon de sulfureto tem 16 prótons que atraem 18 elétrons, enquanto o íon de cálcio tem 20 prótons que atraem o mesmo número de elétrons.Assim, com mais prótons, o cálcio pode puxar os elétrons para muito mais perto do núcleo do que o sulfureto, resultando num íon de cálcio menor do que o íon de sulfureto. Quanto maior for a carga nuclear, menor será o raio, embora a adição de uma camada de elétron interrompa esta tendência. No entanto, o sulfureto é o maior e o cálcio é o menor íon desta série.

radiação iónica

O raio iónico é a medida utilizada para descrever o tamanho de um ião. Um catião tem sempre menos eletrões e o mesmo número de protões do que o átomo que lhe deu origem; é menor do que o átomo de que deriva. Por exemplo, o raio covalente de um átomo de alumínio (1s22s22p63s23p1) é de 118 pm, enquanto que o raio iónico de um Al3+ (1s22s22p6) é de 68 pm. À medida que os eletrões são removidos da camada de valência exterior, os eletrões centrais restantes que ocupam camadas mais pequenas apresentam uma carga nuclear efetiva Zeff maior e são atraídos ainda mais para perto do núcleo.

Catiões com cargas maiores são menores do que catiões com cargas menores (por exemplo, V2+ tem um raio iónico de 79 pm, enquanto que o de V3+ é 64 pm). Ao descer os grupos da tabela periódica, os catiões de elementos sucessivos com a mesma carga têm geralmente raios maiores, correspondendo a um aumento no número quântico principal, n.

Um anião (ião negativo) é formado pela adição de um ou mais eletrões à camada de valência de um átomo. Isto resulta em uma maior repulsão entre os eletrões e em uma diminuição de Zeff por eletrão. Ambos os efeitos (o número aumentado de eletrões e Zeff diminuído) fazem com que o raio de um anião seja maior do que o do átomo que o originou. Por exemplo, um átomo de enxofre ([Ne]3s23p4) tem um raio covalente de 104 pm, enquanto que o raio iónico do anião sulfureto ([Ne]3s23p6) é de 170 pm. Para elementos consecutivos indo para baixo em qualquer grupo, os aniões têm maiores números quânticos principais e, portanto, raios maiores.

Diz-se que átomos e iões que têm a mesma configuração eletrónica são isoeletrónicos. Exemplos de espécies isoeletrónicas são N3–, O2–, F–, Ne, Na+, Mg2+, e Al3+ (1s22s22p6). Outra série isoeletrónica é P3–, S2–, Cl–, Ar, K+, Ca2+, e Sc3+ ([Ne]3s23p6). Para átomos ou iões isoeletrónicos, o número de protões determina o tamanho. Quanto maior a carga nuclear, menor o raio em uma série de iões e átomos isoeletrónicos.

Este texto é adaptado de <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>

Radiação Iónica

O raio iônico é a medida usada para descrever o tamanho de um íon. Um cátion sempre tem menos elétrons e o mesmo número de prótons que o átomo pai; ela...

Education

JoVE Core

Química

Periodic Properties of the Elements

Propriedades Periódicas dos Elementos

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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

periodic classification of the elements

How Valence Electrons Shape the Periodic Table

The periodic table organizes elements by increasing atomic number, and it also shows why elements in the same group behave alike. As the electron configurations are placed into the table, a repeating pattern appears in the outer shells of atoms. These outer electrons are called valence electrons, and they play the biggest role in chemical reactions. They are the highest-energy electrons in an atom, so they are easier to lose or share than core electrons. Valence electrons also help determine...

ionization energy

Ionization Energy Trends in the Periodic Table

Ionization energy is the energy needed to remove an electron from a gaseous atom or ion in its ground state. The first ionization energy, or IE1, removes the most loosely bound electron and forms a 1+ cation. The second ionization energy, IE2, removes the next electron, and each later ionization energy removes another electron from the atom or ion. Ionization always requires energy, so these processes are endothermic. That means ionization energy values are always positive. In general, larger...

atomic radii and effective nuclear charge

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Periodic Trends in Atomic Size

Periodic trends in atomic size help explain why atoms get larger or smaller across the periodic table. Elements in the same group show similar chemical behavior because they have the same number and arrangement of valence electrons. Across a period, each new element adds one proton to the nucleus and one electron to the valence shell. Down a group, the number of valence electrons stays the same, but the principal quantum number increases by one. Atomic radius is not easy to define with perfect...

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...

electron affinity

Electron Affinity Trends on the Periodic Table

Electron affinity is the energy change that happens when a gaseous atom gains an electron and becomes a negative ion, or anion. For many elements, this process releases energy, so the electron affinity value is negative. For some elements, energy must be added instead, so the value is positive. Electron affinity also applies when more than one electron is added. The second electron affinity is the energy change for adding an electron to an anion to make a 2− ion. Later electron affinities...

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Alkali Metals: Reactivity Trends

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halogens

Halogens: Trends and Reactions

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noble gases

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Noble gases are the group 18 elements helium, neon, argon, krypton, xenon, and radon. They were called “noble” because they were once thought to be nonreactive. That idea changed in 1962, when Dr. Neil Bartlett at the University of British Columbia showed that this assumption was not fully correct. These gases occur in very small amounts in the atmosphere. Some natural gas contains 1–2% helium by mass. Helium is separated from natural gas by removing the condensable components, which leaves...

key terms and concepts

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

chemistry

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Physical Science

PS.PSc.1.6

Pennsylvania State Academic Standards

Chemical Reactions

3.2.9-12.C

Structure and Properties of Matter

3.2.9-12.A

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High School

Matter And Its Interactions

HS-PS1-1

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Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Periodic trends of the elements

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Matter and Its Interactions

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CH.2

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Alabama Course of Study Science

9-12.C.1.1

9-12.C.1.1.e

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Motion and Stability: Forces and Interactions

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New York State Science Learning Standards

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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

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Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

How Ionic Charge Changes Ion Size

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