Name: lewis structures, bonds, and formal charge
Uploaded: 2025-05-22T09:05:32.000Z
Duration: 2 min 19 s
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K12 Standards

Tennessee Academic Standards

High School

Chemistry

Matter and Its Interactions

CHEM1.PS1.12

Lewis Structures and Formal Charges

Структуры Льюиса представляют собой упрощенное представление химических связей между атомами. Рассмотрим этен, где два атома углерода с четырьмя валентными электронами каждый окружены четырьмя атомами водорода, имеющими по одному валентному электрону каждый. Следовательно, этен имеет в общей сложности двенадцать валентных электронов.
Требуется двадцать четыре электрона, чтобы удовлетворить октеты для двух атомов углерода и дуэты для четырех атомов водорода. Таким образом, двенадцать электронов должны быть общими для атомов. Поскольку доступно только двенадцать электронов, все они должны быть связующими электронами, чтобы позволить всем атомам достичь стабильной электронной конфигурации.
Иногда атомы в многоатомных структурах не проявляют стандартного числа валентных электронов. В таких случаях ненулевой формальный заряд, F, связан с аномальным атомом. Формальный заряд равен числу валентных электронов на нейтральном атоме за вычетом числа связей и неразделенных электронов на этом атоме.
Например, в ионе аммония каждый атом водорода имеет один валентный электрон в своей нейтральной форме и связан одной связью, что дает формальный заряд, равный нулю.
Это оставляет атом азота с четырьмя валентными электронами вместо обычных пяти валентных электронов. Поскольку в нем отсутствует один электрон, он несет формальный заряд один с плюсом. Таким образом, общий заряд на ион аммония равен одному плюсу.
Стабильные конфигурации обычно минимизируют формальные платежи. Для некоторых более крупных элементов октет может быть расширен до общего числа более восьми электронов для достижения конфигурации с меньшим количеством формальных зарядов.
Например, атом серы в триоксиде серы может образовывать как одинарные, так и двойные связи с окружающими атомами кислорода. Тем не менее, предпочтение отдается схеме с двойной связью, так как она уменьшает общий формальный заряд на атоме.
Другие исключения из правила октета включают борсодержащие соединения, которые имеют мишень в шесть общих электронов, а не восемь, потому что для достижения октета требуется формальный заряд.

Адаптировано из <a href="https://openstax.org/books/chemistry-2e/pages/7-3-lewis-symbols-and-structures">Openstax, Химия 2e, раздел 7.3: Символы и структуры Льюиса</a> и <a href="https://openstax.org/books/chemistry-2e/pages/7-4-formal-charges-and-resonance">Openstax, Химия 2e, Раздел 7.4: Формальные заряды и резонанс</a>.

Структуры Льюиса и формальные заряды

Символы Льюиса можно использовать для обозначения образования ковалентных связей, которые показаны в структурах Льюиса — рисунках, описывающих связи в молекулах и многопятиатомных ионах. Таблицу Менделеева можно использовать для предсказания количества валентных электронов в атоме и количества связей, которые будут образованы для достижения октета. Элементы 18-й группы, такие как аргон и гелий, имеют заполненную электронную конфигурацию и поэтому редко участвуют в химической связи. Однако атомам из группы 17, таким как бром или йод, для достижения октета нужен только один электрон. Следовательно, атомы, принадлежащие к группе 17, могут образовывать одинарную ковалентную связь. Атомам группы 16 нужно два электрона, чтобы достичь октета; следовательно, они могут образовывать две ковалентные связи. Точно так же углероду, принадлежащему к группе 14, нужно еще четыре электрона, чтобы достичь октета; таким образом, углерод может образовывать четыре ковалентные связи.

Рассмотрим структуру Льюиса молекулы хлора:

<img alt="Figure1" src="/files/ftp_upload/11681/PTfigure_1.svg" style="text-align: center; height: 30px;">

Структура Льюиса указывает на то, что каждый атом Cl имеет три пары электронов, которые не используются при связывании (их называют неподеленными парами), и одну общую пару электронов (приписанную к обоим атомам). Штрих (или линия) иногда используется для обозначения общей пары электронов: Cl – Cl.

Одна общая пара электронов называется одинарной связью. Каждый атом Cl взаимодействует с восемью валентными электронами: шестью в неподеленных парах и двумя в одинарной связи. Однако паре атомов может потребоваться иметь более одной пары электронов, чтобы достичь необходимого октета.

 Двойная связь образуется, когда две пары электронов распределяются между парой атомов, как, например, между атомами углерода и кислорода в CH2O (формальдегиде).

<img alt="Figure2" src="/files/ftp_upload/11681/PTfigure_2.svg" style="text-align: center; height: 60px;">

Тройная связь образуется, когда три пары электронов являются общими для пары атомов, как в монооксиде углерода (CO).

<img alt="Figure3" src="/files/ftp_upload/11681/PTfigure_3.svg" style="text-align: center; height: 20px;">

Формальный заряд атома в молекуле — это гипотетический заряд, который имел бы атом, если бы электроны в связях равномерно распределялись между атомами. Формальный заряд можно рассчитать, вычитая сумму числа несвязывающих электронов и числа связей на атоме (или половины числа связывающих электронов) из числа валентных электронов нейтрального атома:

Формальный заряд = # электронов валентной оболочки (свободный атом) − # неподеленных пар электронов − # связей

Расчеты формальных зарядов можно перепроверить, определив сумму формальных зарядов для всей структуры. Сумма формальных зарядов всех атомов нейтральной молекулы должна быть равна нулю; сумма формальных зарядов иона должна равняться заряду иона. Помните, что формальный заряд, рассчитанный для атома, не является фактическим зарядом атома в молекуле. Формальный заряд — это всего лишь полезная математическая процедура; это не указывает на наличие реальных зарядов.

Символы Льюиса можно использовать для обозначения образования ковалентных связей, которые показаны в структурах Льюиса — рисунках, описывающих связь в ...

Education

JoVE Core

Organic Chemistry

Органическая химия

Unit 1

Раздел 1

Covalent Bonding and Structure

Ковалентная связь и структура

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

lewis structures, bonds, and formal charge

Lewis structures show how atoms share electrons in covalent bonds and in polyatomic ions. Lewis symbols help draw these structures, and the periodic table helps predict how many valence electrons an atom has and how many bonds it can form to reach an octet.

Group 18 elements, such as argon and helium, already have filled electron configurations. They rarely take part in chemical bonding. Atoms in group 17, such as bromine and iodine, need one more electron to reach an octet, so they can form one covalent bond. Atoms in group 16 need two electrons, so they can form two covalent bonds. Carbon is in group 14 and needs four more electrons, so it can form four covalent bonds.

The chlorine molecule is a simple example of a Lewis structure. Each Cl atom has three lone pairs, which are electron pairs not used in bonding, and one shared pair between the atoms. A dash or line can show this shared pair, so the bond can be written as Cl–Cl. A single shared pair is a single bond, and each chlorine atom reaches eight valence electrons when its lone pairs and bond are counted.

Some atoms must share more than one pair of electrons to complete an octet. A double bond forms when two pairs of electrons are shared, as in formaldehyde, CH2O, between carbon and oxygen. A triple bond forms when three electron pairs are shared, as in carbon monoxide, CO. These bond types help show how atoms connect in a molecule.

Formal charge is a bookkeeping tool for Lewis structures. It is the hypothetical charge an atom would have if bonding electrons were shared evenly. To calculate it, subtract the number of lone pair electrons and the number of bonds from the number of valence shell electrons in the free atom. The formal charges in a neutral molecule must add to zero, and the formal charges in an ion must add to the ion’s charge. Even so, formal charge is not the same as actual charge on an atom.

Lewis Structures, Bonds, and Formal Charge

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Understand and be prepared to use values specific to chemical processes: the mole, molar mass, molarity, and percent composition. EXPLANATION: During the early and mid-1800s, a tremendous amount of early research poured into building an understanding of the way that atoms combine. This work required analysis of the percent composition of different substances. Joseph Proust's work with tin oxides led him to publish his law of definite proportions noting that a given pure substance will have a constant ratio for the combination of elements making up the substance. Building on Proust's work, John Dalton published his law of multiple proportions and atomic theory noting that multiple patterns exist for the way that atoms combine, yet the combining atoms are invariable. Meanwhile Amedeo Avogadro hypothesizes that given equal pressures and temperatures, two equal volumes of gas will contain equal numbers of atoms. Acknowledging that the exact number of atoms was unknown in these gaseous volumes, the Latin word "mole" was used. "Mole" translates to "lump" recognizing the ambiguous quantity of gas. A number of attempts have been undertaken historically to quantify the mole. Robert Millikan's oil drop experiment revealed the change of a single electron, which could then be divided into Faraday's Constant for the charge of a mole of electrons. Dividing the charge of a mole of electrons by the charge of a single electron yields the number of electrons in a mole, $6.022\times10^{\wedge}23$. Students should be familiar with how to translate between the given quantities. Student's first use atomism/Dalton's atomic theory in third grade noting that matter is made up of particles too small to be seen. This the first time where students will undertake the process of counting these invisible particles. Electrolysis of water provides a tangible experience to demonstrate the constituent parts of water, though the definite proportions of water may not be easily seen due to the solubility of the gasses produced. The concept of relative mass can be explored by comparing small groups of like items. For example, relative masses of beans can be compared with pinto, white, and black beans. If bags are created with equal numbers of like beans, students can develop a concept of why the smallest bean will have a relative mass of 1, analogous to hydrogen.

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CHEM1.PS1.4

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Conduct investigations to explore and characterize the behavior of gasses (pressure, volume, and temperature), develop models to represent this behavior, and construct arguments to explain this behavior. Evaluate the relationship (qualitative and quantitatively) at STP between pressure and volume (Boyle's Law), temperature and volume (Charles' Law), temperature and pressure (Gay-Lussac Law) and moles and volume (Avogadro's Law), and evaluate and explain these relationships with respect to kinetic molecular theory. Be able to understand, establish, and predict the relationships between volume, temperature, and pressure using combined gas law both qualitatively and quantitatively. EXPLANATION: When exploring the behavior of gasses, it is important to consider experimental design. Experiments used to show the relationships between these sets of variables should include one independent and one dependent variable. Other variables should be held constant. Pressure should serve as the dependent variable because it cannot be manipulated directly. Avogadro's Law can be used to relate the amount of gas in two different containers in lieu of knowing actual number of gas particles in an individual container. Individual demonstrations can be performed to explore each of the different gas laws.

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Source: Laboratory of Dr. Andreas Z&#252;ttel - Swiss Federal Laboratories for Materials Science and Technology
The ideal gas law describes the behavior ...

real-gases-effects-intermolecular-forces-molecular-volume-deriving

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and ...

chemical-stoichiometry-gases-using-ideal-gas-law-to-determine

Chemical Stoichiometry and Gases: Using Ideal Gas Law to Determine Moles

Chemical stoichiometry describes the quantitative relationships between reactants and products in chemical reactions.

In addition to measuring quantities ...

pV-Diagrams

The pV diagram, which is a graph of pressure versus volume of the gas under study, is helpful in describing certain aspects of the substance. When the ...

Use the ideal gas law, PV = nRT, to algebraically evaluate the relationship among the number of moles, volume, pressure, and temperature for ideal gases. EXPLANATION: If students have collected data during investigations for CHEM1.PS1.5, these data can then be used to linearize. With pressure assigned as the dependent variable and plotted against (moles) (temperature)/volume, the slope of the graph will be the gas constant, yielding the ideal gas law. After developing the mathematical model, this model can be used to make predictions for other systems.

CHEM1.PS1.6

Separation of Mixtures via Precipitation

Source: Laboratory of Dr. Ana J. Garc&#237;a-S&#225;ez &#8212; University of T&#252;bingen
Most samples of interest are mixtures of many different ...

States of Matter and Phase Changes

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

Distillation: Vapor&ndash;Liquid Equilibria

Distillation is a separation technique that takes advantage of the boiling point properties of disparate elements in a mixture. To perform distillation, ...

Filtration

Filtration is the physical separation of solids from a fluid using a filtration medium.
The filtration medium is chosen depending on the purpose of ...

Centrifugation

Centrifugation is a method of separating suspended particles from a liquid by spinning in a centrifuge at a high number of revolutions per minute.
...

Sublimation

Sublimation is the direct phase transformation from the solid to the gaseous phase, bypassing the liquid state.
For example, solid carbon dioxide, or dry ...

recrystallization-solidsolution-equilibria

Recrystallization: Solid&ndash;Solution Equilibria

Recrystallization is a purification technique used to separate impurities from solid compounds. In this technique, no chemical reactions occur. Instead, ...

Precipitation and Co-precipitation

Precipitation and coprecipitation techniques can be applied to separate a mixture of ions.
When different ions form sparingly soluble salts with the same ...

Electrodeposition

During electrodeposition, ions are separated from a solution by deposition on an electrode in an electrolytic cell.
While reduction occurs at the cathode ...

extraction-partition-and-distribution-coefficients

Extraction: Partition and Distribution Coefficients

The distribution law or Nernst&#39;s distribution law is the law that governs the distribution of a solute between two immiscible solvents. This law, also ...

Extraction: Effects of pH

Consider a weak base,&#160; B, with a partition coefficient, K, between the organic and aqueous phases.&#160;&#160;
While organic bases are usually more ...

Extraction: Advanced Methods

Metal ions can be separated by complexation with organic ligands to form uncharged chelates.
The chelating agent must contain hydrophobic groups and ...

Chromatography: Introduction

Chromatography is a technique used to separate compounds based on differences of partitioning between two phases, the stationary phase and the mobile ...

Dialysis

Dialysis separates desired analyte ions or molecules from unwanted molecules, or &#39;interferents&#39;, by allowing the sample solution to diffuse ...

Analyze solutions to identify solutes and solvents, quantitatively analyze concentrations (molarity, percent composition, and ppm), and perform separation methods such as evaporation, distillation, and/or chromatography and show conceptual understanding of distillation. Construct argument to justify the use of certain separation methods under different conditions. EXPLANATION: In seventh grade, students developed an understanding that chemical and physical properties of a sample of matter could be used to identify a substance. Building on this understanding, students now explore the use of these physical and chemical properties to separate mixtures. Analysis of the substances is performed to aid in further discussion and facilitate further quantitative analysis.

CHEM1.PS1.7

Acids and bases play several important roles in biology. The pH of a biological system can significantly impact the function of biological molecules, ...

Identify acids and bases as a special class of compounds with a specific set of properties. EXPLANATION: The concept of pH is first introduced in seventh grade as a chemical property of matter. Students should be introduced to multiple explanations of acid and base behavior to permit classification of common substances (e.g. baking soda, ammonia, carbon dioxide) as acids or bases. To further develop discussions of solubility, qualitative discussions of the differences between strong and weak acids are appropriate. (Calculations of pH or ion concentrations are beyond the scope of this standard. Discussions of pOH are beyond the scope of this standard. Conjugate pairs are beyond the scope of this standard.)

CHEM1.PS1.8

Lewis Structures, Bonds, and Formal Charge

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