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

K12 Standards

Tennessee Academic Standards

High School

Chemistry

Matter and Its Interactions

CHEM1.PS1.12

Lewis Structures and Formal Charges

Struktury Lewisa są uproszczonymi reprezentacjami wiązań chemicznych między atomami. Weźmy pod uwagę eten, w którym dwa atomy węgla z czterema elektronami walencyjnymi każdy są otoczone czterema atomami wodoru, z których każdy ma jeden elektron walencyjny. Stąd eten ma w sumie dwanaście elektronów walencyjnych.
Potrzeba dwudziestu czterech elektronów, aby zaspokoić oktety dla dwóch atomów węgla i duety dla czterech atomów wodoru. W ten sposób dwanaście elektronów musi być współdzielonych między atomami. Mając do dyspozycji tylko dwanaście elektronów, wszystkie muszą wiązać elektrony, aby umożliwić wszystkim atomom osiągnięcie stabilnej konfiguracji elektronicznej.
Czasami atomy w strukturach wieloatomowych nie wykazują standardowej liczby elektronów walencyjnych. W takich przypadkach niezerowy ładunek formalny, F, jest związany z anomalnym atomem. Ładunek formalny jest równy liczbie elektronów walencyjnych na atomie neutralnym pomniejszonej o liczbę wiązań i niewspółdzielonych elektronów na tym atomie.
Na przykład w jonie amonowym każdy atom wodoru ma jeden elektron walencyjny w postaci obojętnej i jest połączony pojedynczym wiązaniem, co daje ładunek formalny równy zero.
To pozostawia atom azotu z czterema elektronami walencyjnymi zamiast zwykłych pięciu elektronów walencyjnych. Ponieważ brakuje mu jednego elektronu, nosi formalny ładunek jeden z plusem. Zatem całkowity ładunek jonu amonowego jest jeden plus.
Stabilne konfiguracje na ogół minimalizują opłaty formalne. W przypadku niektórych większych pierwiastków oktet może zostać rozszerzony do więcej niż ośmiu elektronów, aby osiągnąć konfigurację z mniejszą liczbą ładunków formalnych.
Na przykład atom siarki w trójtlenku siarki może tworzyć zarówno pojedyncze, jak i podwójne wiązania z otaczającymi atomami tlenu. Jednak preferowany jest układ podwójnych wiązań, ponieważ zmniejsza ogólny ładunek formalny atomu.
Inne wyjątki od reguły oktetu obejmują związki zawierające bor, których celem jest sześć wspólnych elektronów, a nie osiem, ponieważ osiągnięcie oktetu wymaga formalnego ładunku.

Na podstawie <a href="https://openstax.org/books/chemistry-2e/pages/7-3-lewis-symbols-and-structures">Openstax, Chemia 2e, Sekcja 7.3: Symbole i struktury Lewisa</a> oraz <a href="https://openstax.org/books/chemistry-2e/pages/7-4-formal-charges-and-resonance">Openstax, Chemia 2e, Sekcja 7.4: Ładunki formalne i rezonans</a>.

struktury lewisa i ładunki formalne

Symboli Lewisa można użyć do wskazania tworzenia wiązań kowalencyjnych, które pokazano na strukturach Lewisa - rysunkach opisujących wiązania w cząsteczkach i jonach wieloatomowych. Układ okresowy można wykorzystać do przewidywania liczby elektronów walencyjnych w atomie i liczby wiązań, które zostaną utworzone, aby osiągnąć oktet. Pierwiastki z grupy 18, takie jak argon i hel, mają wypełnione konfiguracje elektronowe i dlatego rzadko uczestniczą w wiązaniach chemicznych. Jednak atomy z grupy 17, takie jak brom czy jod, potrzebują tylko jednego elektronu, aby dotrzeć do oktetu. Zatem atomy należące do grupy 17 mogą tworzyć pojedyncze wiązanie kowalencyjne. Atomy grupy 16 potrzebują dwóch elektronów, aby osiągnąć oktet; stąd mogą tworzyć dwa wiązania kowalencyjne. Podobnie węgiel należący do grupy 14 potrzebuje czterech dodatkowych elektronów, aby osiągnąć oktet; w ten sposób węgiel może tworzyć cztery wiązania kowalencyjne.

Rozważmy strukturę Lewisa cząsteczki chloru:

<img alt="Figure1" src="/files/ftp_upload/11681/PTfigure_1.svg" style="text-align: center; height: 30px;">

Struktura Lewisa wskazuje, że każdy atom Cl posiada trzy pary elektronów, które nie są wykorzystywane w wiązaniu (zwane parami samotnymi) i jedną wspólną parę elektronów (zapisaną pomiędzy atomami). Czasami używa się myślnika (lub linii) do wskazania wspólnej pary elektronów: Cl – Cl

Pojedynczą wspólną parę elektronów nazywamy wiązaniem pojedynczym. Każdy atom Cl oddziałuje z ośmioma elektronami walencyjnymi: sześcioma w wolnych parach i dwoma w pojedynczym wiązaniu. Jednak w celu uzyskania wymaganego oktetu może być konieczne współdzielenie więcej niż jednej pary elektronów przez parę atomów.

Wiązanie podwójne powstaje, gdy dwie pary elektronów są wspólne dla pary atomów, tak jak między atomami węgla i tlenu w CH2O (formaldehydzie).

 <img alt="Figure2" src="/files/ftp_upload/11681/PTfigure_2.svg" style="text-align: center; height: 60px;">

Wiązanie potrójne powstaje, gdy trzy pary elektronów są wspólne dla pary atomów, jak w przypadku tlenku węgla (CO).

<img alt="Figure3" src="/files/ftp_upload/11681/PTfigure_3.svg" style="text-align: center; height: 20px;">

 Ładunek formalny atomu w cząsteczce to hipotetyczny ładunek, jaki miałby atom, gdyby elektrony w wiązaniach były równomiernie rozmieszczone pomiędzy atomami. Ładunek formalny można obliczyć odejmując sumę liczby elektronów niewiążących i liczbę wiązań na atomie (lub połowę liczby elektronów wiążących) od liczby elektronów walencyjnych atomu obojętnego:

Ładunek formalny = # elektronów powłoki walencyjnej (wolny atom) - # elektronów w wolnej parze - # wiązań

Obliczenia ładunków formalnych można sprawdzić ponownie, ustalając sumę ładunków formalnych dla całej konstrukcji. Suma ładunków formalnych wszystkich atomów w cząsteczce obojętnej musi wynosić zero; suma ładunków formalnych w jonie powinna być równa ładunkowi jonu. Pamiętaj, że ładunek formalny obliczony dla atomu nie jest rzeczywistym ładunkiem atomu w cząsteczce. Ładunek formalny jest jedynie użyteczną procedurą zapisu; nie wskazuje na obecność rzeczywistych ładunków.

Struktury Lewisa i ładunki formalne

Symbole Lewisa mogą być używane do wskazania tworzenia wiązań kowalencyjnych, które są pokazane w strukturach Lewisa - rysunkach opisujących wiązanie w ...

Education

JoVE Core

Organic Chemistry

Chemia organiczna

Unit 1

Jednostka 1

Covalent Bonding and Structure

Wiązania kowalencyjne i struktura

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

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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Carbon Compounds in Everyday Life

Organic chemistry focuses on carbon compounds called organic compounds. These compounds may come from living things or be made by chemists. Carbon is the main element in them, and it bonds with other carbon atoms as well as hydrogen, oxygen, nitrogen, and sulfur. Carbon can form up to four strong bonds. That ability lets carbon atoms build chains and rings of many sizes, shapes, and levels of complexity. Not every carbon-containing substance is classified as organic. Carbonates, cyanides, and...

electronic structure of atoms

Atomic Orbitals and Quantum Numbers

Atomic orbitals and quantum numbers describe how electrons are arranged around the nucleus. An atom has a small, positively charged nucleus with electrons surrounding it. The nucleus contains protons and neutrons, and the quantum mechanical model gives a better picture of this structure than older models. Protons carry a +1 charge and have a mass of 1.0073 amu. Neutrons have no charge and have a mass of 1.0087 amu. Electrons carry a −1 charge and have a mass of 0.00055 amu. The number of...

electron configurations

How Electrons Fill Atomic Orbitals

Electron filling in atoms follows a set order based on orbital energy. The Aufbau principle says each new electron enters the lowest-energy subshell available. The Pauli exclusion principle says no two electrons can share the same set of four quantum numbers. Hund’s rule of maximum multiplicity says electrons stay unpaired in equal-energy orbitals when possible. The order of filling follows the relative energies of the subshells. A common sequence is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.

chemical bonds

Chemical Bonds: Types and Strength

Chemical bonds help atoms reach a full valence shell like the nearest noble gas. The main bond types are ionic, covalent, and metallic. Bond energy and bond length also help explain how strong a bond is. An ionic bond forms from electrostatic attraction between cations and anions. In many cases, one atom transfers electrons to another atom, and the ions form from that transfer. Ionic bonds have no defined direction because the attraction spreads evenly through three-dimensional space. A...

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Electronegativity in Polar Covalent Bonds

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lewis structures and formal charges

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...

vsepr theory

Molecular Shapes from Electron Pairs

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molecular geometry and dipole moments

Predicting Shape and Molecular Polarity

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resonance and hybrid structures

Resonance in Nitrite and Carbonate Ions

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valence bond theory and hybridized orbitals

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Covalent Bond Overlap and Orbital Hybridization

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Bond Order and Molecular Orbitals

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intermolecular forces and physical properties

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solubility

Why Some Substances Dissolve in Water

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introduction to functional groups

Functional Groups and Organic Molecules

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Advanced Functional Groups in Organic Chemistry

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key terms and concepts

Learn how Lewis structures show bonding, lone pairs, single, double, and triple bonds, and how to calculate formal charge in molecules and ions.

Lewis Structures, Bonds, and Formal Charge | JoVE K12

organic chemistry

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Formula Mass and Mole Concepts of Compounds

Formula Mass of Covalent Compounds

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Determining the Mass Percent Composition in an Aqueous Solution

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Solutions and Concentrations

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Reaction Stoichiometry

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Stoichiometry, Product Yield, and Limiting Reactants

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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.

CHEM1.PS1.1

Chemical Equations

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The Atomic Theory of Matter

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Chemical Reactions

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Balancing Redox Equations

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Demonstrate that atoms, and therefore mass, are conserved during a chemical reaction by balancing chemical reactions. EXPLANATION: Standard 7.PS1.4 explores the idea that chemical reactions are rearrangements of atoms, and students undertake the process of balancing chemical reactions with that standard in seventh grade. The introduction of molar masses in high school makes an explicit connection between the number of atoms, as previously investigated, and the actual masses of the atoms, permitting the collection of more concrete evidence for the conservation of mass in chemical reactions.

CHEM1.PS1.2

Reaction Yield

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A balanced chemical equation provides the information of chemical formulas of the reactants and products involved in the chemical change. A ...

Limiting Reactant

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Chemical Equilibria: Systematic Approach to Equilibrium Calculations

In systems with multiple equilibria, the equilibrium calculations use a systematic approach involving a series of steps to make sure there are as many ...

Perform stoichiometric calculations involving the following relationships: mole- mole; mass-mass; mole-mass; mole- particle; and mass- particle. Show a qualitative understanding of the phenomenon of percent yield, limiting, and excess reagents in a chemical reaction through pictorial and conceptual examples. (states of matter liquid and solid; excluding volume of gasses). EXPLANATION: This standard builds on the idea that balancing chemical reactions provides evidence for conservation of mass and that the behavior of atoms follows predictable patterns. Students now have the opportunity to utilize this understanding as they perform and evaluate chemical reactions. (The concepts of limiting reagent and percent yield are presented; however, students are not expected to determine these values algebraically. Use of molar volume in stoichiometric processes is beyond the scope of this standard.)

CHEM1.PS1.3

Predicting Reaction Outcomes

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Introduction to Chemical Reactions

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Chemical Reactions in Aqueous Solutions

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Precipitation Reactions

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Oxidation-Reduction Reactions

Oxidation&ndash;Reduction Reactions

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Oxidation Numbers

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Acids, Bases and Neutralization Reactions

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Synthesis and Decomposition Reactions

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Types of Chemical Reactions: Exchange and Reversible

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Use the reactants in a chemical reaction to predict the products and identify reaction classes (synthesis, decomposition, combustion, single replacement, double replacement). EXPLANATION: Chemical reactions are rearrangements of atoms that follow predicable patterns. There are patterns both at the macroscopic level in the behavior of some of the reaction classes, as well as patterns in the rearrangements of the atoms underlying the reaction. Students should be able to predict the products of the reactions, which also requires the ability to recognize the general patterns for each type of reaction.

CHEM1.PS1.4

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Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

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Ideal Gas Law

Derivation of the Ideal Gas Law
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Kinetic Theory of an Ideal Gas

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Applications of the Ideal Gas Law: Molar Mass, Density, and Volume

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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.

CHEM1.PS1.5

Ideal Gas Equation

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

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

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pV-Diagrams

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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

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States of Matter and Phase Changes

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Distillation: Vapor&ndash;Liquid Equilibria

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Filtration

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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

Lewis Structures, Bonds, and Formal Charge

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