Name: electronegativity and polar bonds
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 54 s
Channel: JoVE

K12 Standards

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Chemistry

Matter and its Interactions

PS.Chm.3.1

Electronegativity

Неметаллы образуют ковалентные связи через общие электроные пары. Но одинаково ли эти электроны распределяются между обоими атомами, или один атом притягивает электроны больше, чем другой? Модель Льюиса изображает все ковалентные связи как равнораспределенные электроны;тем не менее, это не всегда так.Например, если газообразный азот поместить в электрическое поле, он будет одинаково ориентироваться между полюсами. Но когда газообразный хлористый водород, нейтральная молекула, помещается в электрическое поле, водород ориентируется к катоду, а хлор к аноду, указывая на то, что водород имеет частичный положительный заряд, а хлор частичный отрицательный. Способность атома притягивать к себе электроны называется электроотрицательностью.Таким образом, хлор считается более электроотрицательным, чем водород, поскольку он притягивает к себе общие электроны, сопротивляясь отрыву собственных электронов. Однако это не делает связь ионной. В ионной связи электроны передаются от металлов к неметаллам, тогда как в HCl электроны распределяются неравномерно.Электронная плотность у хлора выше, чем у атома водорода, в результате образуется полярная ковалентная связь. Чем больше разница в электроотрицательности между двумя атомами, тем более полярной будет связь. Таким образом, в дополнение к неполярным ковалентным или ионным связям, полярные ковалентные связи обнаруживаются в большом количестве соединений.Американский химик Линус Полинг изучал энергии, необходимые для разрыва связей в таких молекулах, как двухатомный хлор или водород. Он создал шкалу электроотрицательности на основе термохимических данных, которая помогает предсказать типы связей. Электроотрицательность связана с энергией ионизации и сродством атомов к электрону.В периодической таблице значения электроотрицательности увеличиваются слева направо металлы менее электроотрицательны по сравнению с неметаллами, за исключением переходных металлов. Кроме того, значения электроотрицательности уменьшаются вниз по столбцу и с увеличением размера атома, потому что атомы менее способны притягивать электроны к себе. Фтор, наиболее электроотрицательный элемент, имеет произвольно заданное значение электроотрицательности 3, 98.Франций, с другой стороны, является наименее электроотрицательным элементом со значением электроотрицательности 0, 7. Электроотрицательность не имеет единиц измерения;ее нельзя определить экспериментально.

Электроотрицательность

Является ли связь неполярной или полярной ковалентной, определяется свойством связующих атомов, которое называется электроотрицательностью.  
 
 Значения электроотрицательности элементов были предложены одним из самых известных химиков двадцатого века: Линусом Полингом. Полинг исследовал энергии, необходимые для разрыва связей в гетероядерных молекулах, таких как водород и фторид. Основываясь на полученных значениях, он предположил, что энергия, необходимая для разрыва связи, будет представлять собой среднее значение энергий связи H 2 (436 кДж / моль) и F 2 (155 кДж / моль), т. е. 296 кДж / моль. Однако экспериментально полученная энергия связи HF составляет 565 кДж / моль, что намного выше прогнозируемого значения. Чтобы объяснить это различие, Полинг предположил, что связь должна иметь ионный характер, который определяется концепцией электроотрицательности. & Nbsp; 
 
 Электроотрицательность — это мера склонности атома к оттягиванию электронов (или электронной плотности) к себе.  
 
 электроотрицательность определяет, как общие электроны распределяются между двумя атомами в связи. Чем сильнее атом притягивает электроны в своих связях, тем больше его электрочувствительность. Электроны в полярной ковалентной связи смещаются в сторону более электроотрицательного атома; таким образом, более электроотрицательный атом является атом с частичным отрицательным зарядом. Чем больше разница в электроотрицательности, тем больше поляризация распределения электронов и тем больше частичные заряды атомов. 
 
 <h4>Электрическая и периодическая таблица </h4>
 
 <ul>
 <li>Электрическая чувствительность увеличивается слева направо в течение периода в таблице периодического действия и уменьшается в группе.  </li>
 <li>Значения электрочувствительности, полученные Полингом, следуют предсказуемым периодическим трендам, при этом более высокие электрические характеристики будут направлены в верхнюю правую часть периодической таблицы. </li>
 <li>Таким образом, неметаллы, лежащие в правом верхнем углу, имеют тенденцию иметь самые высокие электрические характеристики, при этом фтор является самым электрическим элементом всех (EN = 4.0).  </li>
 <li>Металлы, как правило, менее электрификативные элементы, а металлы группы 1 имеют самые низкие электрические характеристики.  </li>
 <li>Благородные газы исключаются из списка электроотрицательности, так как эти атомы обычно не используют электроны совместно с другими атомами, так как они имеют полную оболочку валентности. (Несмотря на существование таких благородных газовых соединений, как XeO2, они могут формироваться только в экстремальных условиях и, таким образом, не вписываются в общую модель электроотрицательности.) </li>
 </ul>
 
 <h4>Сравнение электронечувствительности с электроникой </h4>
 
 Будьте осторожны, чтобы не запутать электронегативность и сродство электронам. Сродство электронам элемента является измеримым физическим количеством, а именно энергией, высвобождаемой или поглощенной, когда атом изолированной газовой фазы приобретает электрон, измеряемое в кДж/моль. С другой стороны, электроотрицательность описывает, как сильно атом притягивает электроны в связи. Это не измеряемое количество, которое рассчитывается, а не измеряется. Полинг производили первые значения электроотрицательности, сравнив количество энергии, необходимое для разрыва различных типов связей. Он выбрал произвольную относительную шкалу от 0 до 4. 
 
 Этот текст адаптирован из <a href=""https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding"">Openstax, Химия 2е изд., раздел: 7.2 Ковалентная связь.</a>

Является ли связь неполярной или полярной ковалентной, определяется свойством связывающих атомов, называемым электроотрицательностью. 

Значения электроотрицательности ...

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Chemical Bonding: Basic Concepts

Химическая связь: основные понятия

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

electronegativity and polar bonds

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond.

Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The experimental bond energy of HF was much higher, at 565 kJ/mol, which suggested the bond had some ionic character.

In a polar covalent bond, the shared electrons shift toward the more electronegative atom. That atom carries the partial negative charge. The larger the electronegativity difference between two atoms, the more the electrons are pulled to one side, and the larger the partial charges become.

Electronegativity follows clear periodic trends. It increases from left to right across a period and decreases down a group. As a result, the highest values are found toward the upper right of the periodic table, especially among nonmetals. Fluorine is the most electronegative element, with a value of 4.0, while group 1 metals have the lowest values. Noble gases are usually left off electronegativity lists because they already have full valence shells and usually do not share electrons. Some noble gas compounds, such as XeO2, can form only under extreme conditions.

Do not confuse electronegativity with electron affinity. Electron affinity is the measurable energy released or absorbed when an isolated gas-phase atom gains an electron. Electronegativity is different. It describes how strongly an atom attracts electrons in a bond, so it is calculated rather than measured. Pauling placed these values on an arbitrary relative scale from 0 to 4.

Electronegativity and Polar Bonds

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electronegativity

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond. Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The...

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Learn how electronegativity explains polar covalent bonds, Pauling’s bond-energy idea, periodic trends, and the difference from electron affinity.

Electronegativity and Polar Bonds | JoVE K12

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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.

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Electronegativity and Polar Bonds

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