Name: lattice energy patterns in ionic solids
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 54 s
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Trends in Lattice Energy: Ion Size and Charge

Энергия решетки связана с образованием или разделением ионной решетки. Тем не менее, когда образуются хлорид натрия или оксид магния, их энергия решетки значительно различается. Почему каждое ионное соединение имеет разную энергию решетки и от каких факторов она зависит?Ионное соединение состоит из упорядоченно расположенного большого количества ионов, притягиваемых друг к другу электростатическими взаимодействиями. Согласно закону Кулона, потенциальная энергия двух ионов обратно пропорциональна расстоянию между ионами, которое, в свою очередь, зависит от радиуса ионов. В периодической таблице радиус ионов щелочных и щелочноземельных металлов увеличивается вниз по столбцу.По мере увеличения размера иона металла расстояние между ионами или длина связи также увеличивается. Например, длина связи бромида лития и бромида калия 217 и 282 мкм соответственно. Из-за увеличения межъядерного расстояния притяжение между ионами уменьшается, и ионы становится намного легче разделить.Таким образом, энергия решетки для отделения твердого бромида лития больше, чем для бромида калия, и составляет 807 килоджоулей на моль по сравнению с 682 килоджоулями на моль, соответственно. Помимо ионного радиуса, величина энергии решетки также зависит от зарядов ионов. Согласно закону Кулона, потенциальная энергия ионов прямо пропорциональна произведению их зарядов.Рассмотрим два ионных соединения:фторид натрия и оксид кальция. Расстояние между ионами в обоих соединениях одинаково, но энергия решетки оксида кальция почти в четыре раза больше, чем у фторида натрия. И натрий, и фторид являются одновалентными ионами;произведение их заряда равно 1.Однако ионы кальция и оксида двухвалентны, и произведение их заряда равно 4, что в четыре раза больше, чем у фторида натрия. Вот почему для разделения оксида кальция на газообразные ионы требуется почти в четыре раза больше энергии по сравнению с фторидом натрия. Таким образом, величина энергии решетки прямо пропорциональна произведению зарядов ионов и обратно пропорциональна расстоянию между ионами.

Тенденции изменения энергии решетки: размер и заряд ионов

Ионное соединение стабильно из-за электростатического притяжения между его положительными и отрицательными ионами. Решетчатая энергия соединения является мерой прочности этого притяжения. Энергия решетки (ΔHlattice) ионного соединения определяется как энергия, необходимая для разделения одного моль твердого тела на его компонентные газообразные ионы. Для ионного твёрдого хлорида натрия энергия решетки является энтальпией изменения процесса: 
 
 <img alt=""Eq1"" src=""https://www.jove.com/files/core/CDNSource/lessons/1058/1058_Equations-01.png"" style=""height: 40px;"" />
 
 <h4>Соглашения </h4>
 
 Здесь используется соглашение, при котором твердое ионное вещество разделяется на ионы, что означает, что энергии решетки будут эндотермическими (положительные значения). Другой способ - использовать эквивалентное, но противоположное соглашение, в котором энергия решетки является экзотермической (отрицательные значения) и описывается как энергия, выделяемая при объединении ионов в решетку. Таким образом, убедитесь, что подтвердили, какое определение используется при поиске энергий решетки в другом справочнике. В обоих случаях большее значение энергии решетки указывает на более стабильное ионное соединение. Для хлорида натрия & Delta; H решетка = 769 кДж. Таким образом, для разделения одного моля твердого NaCl на газообразные ионы Na + и Cl & ndash; требуется 769 кДж. Когда по одному моль каждого из газообразных ионов Na + и Cl & ndash; образует твердый NaCl, выделяется 769 кДж тепла. 
 
 <h4>Закон Колона и энергия решётки </h4>
 
 Решетчатая энергия ΔHlattice ионного кристалла может быть выражена следующим уравнением (производным от закона Кулона, регулирующего силы между электрическими зарядами):  
 
 ΔHlattice =  C(Z +)(Z-)/ro  
 
 В котором C — константа, зависящая от типа кристаллической структуры; Z+ и Z — заряды на ионы, а Ro — межионное расстояние (сумма радиусов положительных и отрицательных ионов). Таким образом, энергия решетки ионного кристалла быстро увеличивается по мере увеличения зарядов ионов и уменьшения размеров ионов. Когда все остальные параметры остаются неизменными, удвоение заряда катиона и аниона в четыре раза увеличивает энергию решетки.  
 
 <h4>Примеры </h4>
 
 <ol>
 <li>Решетчатая энергия LIF (Z+ и Z– = 1) составляет 1023 кДж/моль, в то время как энергия MgO (Z+ и Z– = 2) составляет 3900 кДж/моль (Ro почти одинакова — около 200 вечера для обоих соединений). </li>
 <li>Различные межатомные расстояния производят разные энергии решетки. Например, сравните энергию решетки MgF2 (2957 кДж/моль) с энергией MgI2 (2327 кДж/моль), чтобы наблюдать влияние на энергию решетки меньшего ионного размера F– по сравнению с i–. </li>
 <li> Драгоценный камень рубин - это оксид алюминия Al 2 O 3 , содержащий следы Cr 3+ . Соединение Al 2 Se 3 используется при изготовлении некоторых полупроводниковых устройств. В этих двух ионных соединениях заряды Z + и Z & ndash; одинаковы, поэтому разница в энергия решетки зависит от R o . Поскольку ион O 2 & ndash; меньше, чем ион Se 2 & ndash; , ион Al 2 O 3 имеет меньшее межионное расстояние, чем Al 2 Se 3 , и, следовательно, имеет большую энергию решетки. </ Li >
 <li> Другой пример - оксид цинка ZnO по сравнению с NaCl. ZnO имеет большую энергию решетки, потому что значения Z как для катиона, так и для аниона в ZnO больше, а межионное расстояние ZnO меньше, чем у NaCl. </li>
 </ol>
 
 Этот текст адаптирован из <a href=""https://openstax.org/books/chemistry-2e/pages/7-5-strengths-of-ionic-and-covalent-bonds"">Openstax, Химия 2е изд., раздел 7.5: Силы ионных и ковалентных связей.</a>

Ионное соединение стабильно благодаря электростатическому притяжению между его положительными и отрицательными ионами. Энергия решетки соединения – это мера...

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lattice energy patterns in ionic solids

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound.

For ionic crystals, lattice energy follows a pattern based on charge and ion size. The relationship can be written as ΔH lattice = C(Z+)(Z−)/Ro. In this equation, C depends on the crystal structure, Z+ and Z− are the ion charges, and Ro is the distance between the ions. Because of this, lattice energy rises quickly when ion charges increase and when ion sizes decrease. If both ion charges double, the lattice energy becomes four times larger.

Examples show these trends clearly. LiF, with ion charges of 1 and 1, has a lattice energy of 1023 kJ/mol, while MgO, with charges of 2 and 2, has a lattice energy of 3900 kJ/mol. Their interionic distances are nearly the same, at about 200 pm. Ion size also matters. MgF2 has a lattice energy of 2957 kJ/mol, while MgI2 has a lower value of 2327 kJ/mol because F− is smaller than I−.

The same idea explains differences in other compounds. Ruby is aluminum oxide, Al2O3, and it contains traces of Cr3+. Al2Se3 is used in some semiconductor devices. These compounds have the same ion charges, so the difference in lattice energy depends on Ro. O2− is smaller than Se2−, so Al2O3 has the shorter interionic distance and the larger lattice energy. ZnO also has a larger lattice energy than NaCl because the ion charges are greater and the interionic distance is smaller.

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trends in lattice energy: ion size and charge

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound. For ionic crystals, lattice energy follows a pattern based on charge and ion size. The...

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How Bond Polarity Shapes Molecular Dipoles

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Learn how ion charge and ion size affect lattice energy in ionic solids, with examples like NaCl, LiF, MgO, MgF2, MgI2, Al2O3, and ZnO.

Lattice Energy Patterns in Ionic Solids | JoVE K12

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An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

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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.

Analyze the structure of atoms and isotopes.

Lattice Energy Patterns in Ionic Solids

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