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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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

Electronegativity

אל-מתכות יוצרות קשרים קוולנטיים על ידי שיתוף אלקטרונים. אך האם אלקטרונים אלה משותפים במידה שווה על ידי שני האטומים או שאחד האטומים מושך את האלקטרונים יותר מהאחר? מודל לואיס מתאר את כל הקשרים הקוולנטיים עם שיתוף אלקטרונים במידה שווה, אך זהו לא תמיד המצב.לדוגמה, אם חנקן גזי נמצא בשדה חשמלי, הוא יימצא במידה שווה בין הקטבים. אבל כשמימן כלורי גזי, שהוא מולקולה ניטרלית, ממוקם בשדה חשמלי, המימן קרוב יותר לקתודה והכלור קרוב יותר לאנודה, מה שמצביע על כך שלמימן יש מטען חיובי חלקי ולכלור יש מטען שלילי חלקי. יכולתו של אטום למשוך אלקטרונים לעברו נקרא אלקטרושליליות.לכן ניתן לומר שכלור הוא אלקטרושלילי יותר ממימן ומושך אליו את האלקטרונים המשותפים, תוך התנגדות לגריעת האלקטרונים שלו. יחד עם זאת, אין זה הופך את הקשר ליוני. בקשר יוני, אלקטרונים מועברים ממתכות לאל-מתכות, בעוד שב-HCl האלקטרונים משותפים במידה לא שווה.צפיפות האלקטרונים גבוהה יותר על הכלור מאשר על אטום המימן, מה שיוצר קשר קוולנטי קוטבי. ככל שההבדל באלקטרושליליות בין האטומים גדול יותר, כך הקשר יהיה קוטבי יותר. לכן, בנוסף לקשרים קוולנטיים לא קוטביים או קשרים יוניים, ניתן למצוא קשרים קוולנטיים קוטביים במגוון רחב של תרכובות.הכימאי האמריקאי לינוס פאולינג חקר את האנרגיות הנדרשות כדי לנתק קשרים במולקולות כגון כלור דיאטומי או מימן. הוא פיתח סולם אלקטרושליליות על סמך נתונים תרמוכימיים, מה שעוזר לחזות סוגי קשרים. אלקטרושליליות מקושרת לאנרגיית יינון ולזיקה האלקטרונית של האטומים.בטבלה המחזורית ערכים אלקטרושליליים גדלים משמאל לימין מתכות הן פחות אלקטרומגנטיות מאל-מתכות, למעט מתכות מעבר. בנוסף לכך, ערכי האלקטרושליליות יורדים במורד הטור ועם העלייה בגודל האטומי, מפני שאטומים פחות יכולים למשוך אלקטרונים לעברם. לפלואור, היסוד הכי אלקטרושלילי, יש ערך אלקטרושלילי שנקבע בשרירותיות של 3.98.פרנציום, לעומת זאת, הוא היסוד הכי פחות אלקטרושלילי עם ערך אלקטרושליליות של 0.7. לאלקטרושליליות אין כל יחידה, היא לא יכולה להיקבע באמצעות ניסוי.

אלקטרושליליות

<div style="direction:rtl">אם הקשר הוא לא קוטבי או קוולנטי קוטבי נקבעת על ידי תכונה של אטומים מקשרים הנקראת אלקטרושליליות. ערכי האלקטרושליליות של היסודות הוצעו על ידי אחד הכימאים המפורסמים ביותר של המאה העשרים: לינוס פאולינג. פאולינג חקר את האנרגיות הנדרשות לשבירת קשרים במולקולות הטרו-גרעיניות כמו מימן ופלואוריד. בהתבסס על הערכים, הוא הציע שהאנרגיה הנדרשת לשבירת קשר תהיה הממוצע של אנרגיות הקשר של H2 (436 קילו-ג'ול/מול) ו-F2 (155 קילו-ג'ול-מול), כלומר 296 קילו-ג'ול-מול. עם זאת, אנרגיית הקשר המתקבלת בניסוי של HF היא 565 קילו ג'ול/מול, שהוא הרבה יותר גבוה מהערך החזוי. כדי להסביר את ההבדל הזה, פאולינג הציע שהקשר חייב להיות בעל אופי יוני, שנקבע על ידי המושג של אלקטרושליליות. אלקטרושליליות היא מדד לנטייתו של אטום למשוך אלקטרונים (או צפיפות אלקטרונים) כלפי עצמו. האלקטרושליליות קובעת כיצד האלקטרונים המשותפים מתחלקים בין שני האטומים בקשר. ככל שאטום מושך חזק יותר את האלקטרונים בקשרים שלו, האלקטרושליליות שלו גדולה יותר. אלקטרונים בקשר קוולנטי קוטבי מוזזים לעבר האטום האלקטרושלילי יותר; לפיכך, האטום האלקטרושלילי יותר הוא זה עם המטען השלילי החלקי. ככל שההבדל באלקטרושליליות גדול יותר, כך התפלגות האלקטרונים מקוטבת יותר והמטענים החלקיים של האטומים גדולים יותר. <h4>אלקטרושליליות והטבלה המחזורית</h4> <ul style="padding-right: 35px; list-style-type: disc;"> <li style="text-align: right;">האלקטרושליליות עולה משמאל לימין לאורך המחזור בטבלה המחזורית ויורדת על פני הקבוצה. </li> <li style="text-align: right;">ערכי האלקטרושליליות שנגזרו על ידי פאולינג עוקבים אחר מגמות מחזוריות הניתנות לחיזוי, כאשר האלקטרושליליות הגבוהות יותר לכיוון הימין העליון של הטבלה המחזורית.</li> <li style="text-align: right;">לפיכך, הלא-מתכות, השוכנות בפינה הימנית העליונה, נוטות להיות בעלות האלקטרושליליות הגבוהות ביותר, כאשר הפלואור הוא היסוד האלקטרושלילי ביותר מכולם (EN = 4.0). </li> <li style="text-align: right;">מתכות נוטות להיות יסודות פחות אלקטרוניים, ולמתכות מקבוצה 1 יש את האלקטרושליליות הנמוכה ביותר. </li> <li style="text-align: right;">גזים אצילים אינם נכללים מרשימת האלקטרושליליות מכיוון שלרוב אטומים אלו אינם חולקים אלקטרונים עם אטומים אחרים מכיוון שיש להם קליפת ערכיות מלאה. (בעוד שתרכובות גז אצילות כגון XeO2 אכן קיימות, הן יכולות להיווצר רק בתנאים קיצוניים, ולכן הן אינן משתלבות בצורה מסודרת במודל הכללי של אלקטרושליליות.)</li> </ul> <h4>אלקטרושליליות מול זיקה אלקטרונית</h4> היזהר לא לבלבל בין אלקטרושליליות לבין זיקה אלקטרונית. זיקת האלקטרון של יסוד היא כמות פיזיקלית הניתנת למדידה, כלומר, האנרגיה המשתחררת או הנספגת כאשר אטום מבודד בשלב גז רוכש אלקטרון, הנמדד בקילו-ג'ול/מול. אלקטרושליליות, לעומת זאת, מתארת באיזו חוזקה אטום מושך אלקטרונים בקשר. זוהי כמות חסרת מימד שמחושבת, ולא נמדדת. פאולינג הסיק את ערכי האלקטרושליליות הראשונים על ידי השוואת כמויות האנרגיה הנדרשות לשבירת סוגים שונים של קשרים. הוא בחר בסולם יחסי שנע בין 0 ל-4. טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Chemistry 2e, Section: 7.2 Covalent Bonding.</a></div>

השאלה אם קשר הוא לא קוטבי או קוולנטי קוטבי נקבעת על ידי תכונה של אטומי הקשר הנקראת אלקטרושליליות. 

ערכי אלקטרושליליות של ...

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כימיה

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Chemical Bonding: Basic Concepts

קשרים כימיים: מושגים בסיסיים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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

types of chemical bonds

Chemical Bonding and Bond Properties

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O. Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence...

the born-haber cycle

Predicting Ionic Stability with Lattice Energy

Lattice energy helps explain why ionic compounds are stable. It measures the strength of attraction between positive and negative ions in a crystal. In one common definition, lattice energy is the energy required to separate one mole of an ionic solid into gaseous ions, so it has a positive value. Another definition uses the opposite sign and describes the energy released when gaseous ions form a lattice. When checking data, it is important to confirm which convention is being used. In either...

lewis symbols and the octet rule

Valence Electrons, Lewis Symbols, and Bonding

Chemical bonds form when atoms or ions interact in ways that lower the potential energy of a molecule. Gilbert N. Lewis created a simple model to show bond formation using valence electrons, the electrons in the outer shell. In this model, electrons are shared or transferred to help atoms reach a stable electron configuration. The Lewis model helps describe two common bond types. An ionic bond forms when electrons move from a metal to a nonmetal. A covalent bond forms when two nonmetals share...

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...

ionic bonding and electron transfer

Ionic Compounds and Crystal Lattices

Ionic compounds form when positive and negative ions attract each other. A cation is a positive ion, and it forms when an atom loses one or more valence electrons. An anion is a negative ion, and it forms when an atom gains one or more valence electrons. Compounds made of these ions are called ionic compounds, or salts, and the force between them is an ionic bond. The properties of ionic solids help show how strong this attraction is. They usually form rigid, brittle crystals and have high...

trends in lattice energy: ion size and charge

trends-in-lattice-energy-ion-size-and-charge

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...

covalent bonding and lewis structures

Shared Electrons in Covalent Molecules

Covalent molecules form when atoms share electrons instead of transferring them. This bonding usually happens between nonmetal atoms with similar tendencies to attract electrons. Because the atoms pull on the electrons in a shared way, the bond is held together by mutual attraction. Covalent compounds often have physical properties that differ from ionic compounds. The attraction between neutral molecules is weaker than the attraction between charged ions. As a result, many covalent compounds...

bond polarity, dipole moment, and percent ionic character

bond-polarity-dipole-moment-and-percent-ionic-character

How Bond Polarity Shapes Molecular Dipoles

Bond polarity depends on electronegativity, the ability of an atom to attract shared electrons. The absolute value of the electronegativity difference, or ΔEN, gives a rough guide to bond type. When the difference is very small or zero, the bond is covalent and nonpolar. When it is larger, the bond may be polar covalent or ionic. Examples show how this works in real compounds. H–H has a ΔEN of 0, so it is nonpolar. H–Cl has a ΔEN of 0.9, so it is polar covalent. Na–Cl has a ΔEN of 2.1, so it...

lewis structures of molecular compounds and polyatomic ions

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Drawing Lewis Structures with Valence Electron Counts

Drawing Lewis structures starts with counting valence electrons and building the atom arrangement step by step. Valence electrons are the outer-shell electrons that help show how atoms bond. For ions, a positive charge means one electron is removed for each plus sign, and a negative charge means one electron is added for each minus sign. The next step is to sketch the skeleton structure. The least electronegative atom usually goes in the center, while hydrogen is almost never central. Fluorine...

resonance

Resonance Forms in Lewis Structures

Resonance forms in Lewis structures help explain molecules and ions that cannot be shown correctly with just one drawing. In nitrite ion, NO2−, the Lewis structure can be drawn in two ways. The N-O and N=O bonds switch positions in the two drawings, but the atoms stay in the same arrangement. If nitrite really had one single bond and one double bond, the two bond lengths should be different. A double bond is shorter and stronger than a single bond between the same atoms. Experiments show that...

formal charges

Lewis Structures with Formal Charge

Lewis structures can sometimes show more than one reasonable arrangement for a molecule or polyatomic ion. Formal charge helps chemists choose the best Lewis structure when that happens. It is a useful way to compare possible structures in chemistry. Formal charge is the hypothetical charge an atom would have if bonding electrons were shared evenly between the atoms. It can also be found by starting with the valence electrons of the neutral atom, subtracting the nonbonding electrons, and then...

exceptions to the octet rule

Octet Rule Exceptions in Lewis Structures

Some covalent molecules do not follow the octet rule in their Lewis structures. Their central atoms can fall into three groups: odd-electron molecules, electron-deficient molecules, and hypervalent molecules. These cases show why a Lewis structure may not always give every atom eight valence electrons. Odd-electron molecules have an odd number of valence electrons, so one electron remains unpaired. Molecules with an odd number of electrons are called radicals. Nitric oxide, NO, is one example,...

bond energies and bond lengths

How Bond Energy Predicts Reaction Heat

Bond energy helps explain why molecules stay together and how much heat a reaction may release or absorb. A covalent bond is stronger when more energy is needed to separate the atoms. The energy needed to break one specific covalent bond in one mole of gaseous molecules is called bond energy, or bond dissociation energy. For a diatomic molecule, bond energy is the standard enthalpy change for an endothermic reaction that breaks that bond. The H-H bond is a common example. Its bond energy is...

bonding in metals

Electron Sea Model in Metals

Electron sea model explains how metallic bonding holds metals together. In this model, most metal atoms do not have enough valence electrons to form ionic or covalent bonds in the usual way. Their valence electrons are held loosely because metals have low electronegativity, and their ionization energy is low, so electrons are removed easily. When a metal atom loses these outer electrons, it becomes a positively charged metal ion. The freed electrons form a delocalized electron cloud around...

key terms and concepts

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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Physical Science

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Scientific Laws

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The Scientific Method

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Matter: Pure Substances and Mixtures
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Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

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Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

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The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

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Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

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Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

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

PS.Chm.2.2

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

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

Trends in Lattice Energy: Ion Size and Charge

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 ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

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.

Electronegativity and Polar Bonds

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