Name: shielding and orbital penetration
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 3 min 21 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry and Physics

IPC.7

IPC.7.E

The Energies of Atomic Orbitals

לאורביטלים אטומיים אנרגיות שונות, כפי שמוסבר באמצעות חוק האינטראקציות של קולון, אפקט המיסוך והחדירה האורביטלית. על פי החוק של קולון, לכוח מושך או דוחה בין שני חלקיקים טעונים יש יחס ריבועי הפוך למרחק ביניהם. הגדלים של אורביטלי האטום גדלים בהתאם למספר הקליפה, ואלקטרונים נדחים מהשטח המאוכלס על ידי אורביטלי הקליפה התחתונה.לכן, לפי חוק קולון, ככל שמספר הקליפה גדל, האלקטרונים חווים פחות משיכה לגרעין, בהלימה עם אנרגיות אורביטליות גבוהות יותר. בנוסף לכך, לאלקטרונים שנמצאים בערך באותו מרחק מהגרעין או קרוב יותר אליו יש אפקט מיגון שמפחית עוד יותר את המשיכה אל הגרעין. ככל שהמיגון גדול יותר, מורגשת פחות משיכה לגרעין.זאת אחת הסיבות להבדלים באנרגיות אורביטליות בין קליפות אלקטרונים. לדוגמה, אלקטרונים מסוג 3s ו-3p ממסכים במידה משמעותית על אלקטרוני 3d. המטען הגרעיני בפועל שאלקטרון חש מחושב על ידי הפחתת קבוע המיסוך S, שתלוי במספר האלקטרונים הממסכים ובתתי קליפות המשנה שהם מאכלסים, מהמספר האטומי.לדוגמה, שני האלקטרונים ברמת 1s בליתיום, שמספרם האטומי הוא 3 ממסכים את אלקטרוני 2S שלו. קבוע המיסוך של אותו אלקטרון נקבע על פי כללים נסיוניים למחצה כ-1.7. לכן המטען הגרעיני בפועל המורגש על ידי אלקטרון 2S הוא 1.3.גם הצורות האורביטליות מכתיבות את האנרגיה שלהם. אם האלקטרונים באורביטל חיצוני יכולים לנוע הרחק לאזורים המאוכלסים על ידי אלקטרונים פנימיים כדי להתקרב לגרעין, הם יהיו ממוסכים הרבה פחות שם. לכן האנרגיה של אותו אורביטל חיצוני נמוכה יותר.ניתן לדמיין זאת באמצעות התפלגות רדיאלית, פונקציה המתארתאת ההסתברות של מציאת אלקטרון במרחק נתון מהגרעין. שרטוט פונקציות התפלגות רדיאלית עבור תתי קליפות 1s, 2s ו-2p מגלה כי קיימת סבירות נמוכה שאלקטרוני 2s יהיו קרובים לגרעין, ואילו אלקטרוני 2p נשארים בעיקר בחוץ או בקצה החיצוני של אזור 1s. ניתן לומר, אם כן, כי אורביטל 2s הוא בעל יכולת חדירה גדולה יותר.בקליפה השלישית, אלקטרוני 3s הם החודרים ביותר ואלקטרוני 3d הכי פחות חודרים. אנרגיה אורביטלית אטומית עולה בדרך כלל עם מספר הקליפה וברמת תת הקליפה, עולה מ-s ועד f. יחד עם זאת, אפקט החדירה הופך כה משמעותי בקליפות הרביעית והחמישית עד שאורביטלי 4s ו-5s הם לעיתים קרובות בעלי אנרגיות נמוכות יותר באופן יחסי לעומת אורביטלי 3d ו-4d בהתאמה.

אנרגיות של אורביטלים אטומיים

<div style="direction:rtl">

באטום, האלקטרונים הטעונים שלילי נמשכים לגרעין הטעון חיובי. באטום רב-אלקטרוני ניתן לראות גם דחיית אלקטרון-אלקטרון. כוחות המשיכה והדחיה תלויים במרחק בין החלקיקים, כמו גם בסימן ובגודל המטענים על החלקיקים הבודדים. כאשר המטענים על החלקיקים מנוגדים, הם מושכים זה את זה. אם לשני החלקיקים יש אותו מטען, הם דוחים זה את זה. 

ככל שגודל המטענים גדל, גודל הכוח גדל. אולם כאשר הפרדת המטענים גדולה יותר, הכוחות פוחתים. לפיכך, כוח המשיכה בין אלקטרון לגרעין שלו עומד ביחס ישר למרחק ביניהם. אם האלקטרון קרוב יותר לגרעין, הוא קשור בצורה הדוקה יותר לגרעין; לכן, לאלקטרונים בקליפות שונות (במרחקים שונים) יש אנרגיות שונות. 

עבור אטומים בעלי רמות אנרגיה מרובות, האלקטרונים הפנימיים מגנים חלקית על האלקטרונים החיצוניים מפני המשיכה של הגרעין, עקב דחיית אלקטרון-אלקטרון. אלקטרוני הגרעין מגנים על אלקטרונים בקליפות החיצוניות, בעוד שאלקטרונים באותה קליפת ערכיות אינם חוסמים את המשיכה הגרעינית שהם חווים זה מזה בצורה יעילה באותה מידה. ניתן להסביר זאת באמצעות המושג של מטען גרעיני יעיל, "זף". זוהי המשיכה המופעלת על אלקטרון ספציפי על ידי הגרעין, תוך התחשבות בכל דחיית אלקטרון-אלקטרון. למימן, יש רק אלקטרון אחד, ולכן המטען הגרעיני (Z) והמטען הגרעיני האפקטיבי (זף) שווים. עבור כל שאר האטומים, האלקטרונים הפנימיים מגנים חלקית על האלקטרונים החיצוניים מפני המשיכה של הגרעין, וכך:

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/985/985_Equations-01.png" style="height: 40px;"> 

חדירה לאורביטל מתארת את היכולת של אלקטרון להיות קרוב יותר לגרעין. האלקטרונים ב-אורביטל s יכולים להתקרב לגרעין ולהיות בעלי יכולת חדירה יותר גדולה. צפיפות ההסתברות עבור אורביטל s כדורי אינה אפס בגרעין. לתת-קליפות שונות יש אוריינטציות מרחביות שונות. בשל האורביטל בצורת משקולת, ה-p-אלקטרון חודר הרבה פחות. לפונקציית הגל שלו יש צומת העוברת דרך הגרעין, שבו ההסתברות למצוא את האלקטרון היא אפס. לפיכך, אלקטרון באורביטל s קשור בצורה הדוקה יותר לגרעין ויש לו אנרגיה נמוכה יותר מאשר האלקטרון p. ל-d-אלקטרון יש חדירה נמוכה עוד יותר ואנרגיה גבוהה יותר מאלקטרון אורביטלי p.

עבור קליפות ותת-קליפות שונות, ניתן לתאר את מגמת הכוח החדירה של האלקטרון באופן הבא

<img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/985/985_Equations-02.png" style="height: 40px;"> 

השפעת המיגון והחדירה גדולה, ואלקטרון 4s עשוי להיות בעל אנרגיה נמוכה יותר מאלקטרון 3d. 

טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/6-4-electronic-structure-of-atoms-electron-configurations">Openstax, Chemistry 2e, Section 6.4: Electronic Structure of Atoms (Electron Configurations).</a></div>

באטום, האלקטרונים הטעונים שלילית נמשכים לגרעין הטעון חיובית. באטום רב-אלקטרונים, דחיות אלקטרונים-אלקטרונים הן ...

Education

JoVE Core

Chemistry

כימיה

אחד

Electronic Structure of Atoms

מבנה אלקטרוני של אטומים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

shielding and orbital penetration

Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart.

An electron that stays closer to the nucleus is held more tightly. That means electrons in different shells can have different energies because they sit at different distances from the nucleus. In atoms with several energy levels, inner electrons partly block the nucleus from outer electrons. This blocking is called shielding, and it happens because of electron-electron repulsions.

The pull felt by one electron after shielding is the effective nuclear charge, or Zeff. It describes the attraction from the nucleus after repulsions are taken into account. For hydrogen, which has only one electron, Z and Zeff are the same. In atoms with more than one electron, core electrons shield outer electrons, while electrons in the same valence shell do not block the nuclear pull very well.

Orbital penetration describes how close an electron can get to the nucleus. s orbitals penetrate best because their spherical probability density is non-zero at the nucleus. p orbitals penetrate less because their dumbbell shape has a node through the nucleus, where the chance of finding an electron is zero. d orbitals penetrate even less than p orbitals.

Because of shielding and penetration, s electrons are usually bound more tightly and have lower energy than p electrons. d electrons have higher energy than p electrons. These effects can be strong enough that a 4s electron may have lower energy than a 3d electron.

Shielding and Orbital Penetration

the wave nature of light

Measuring Light with Wavelength and Frequency

Light can be described as an electromagnetic wave, and its behavior helps explain many patterns seen in science. For centuries, scientists have tried to understand light. Newton used lenses and prisms to show that white light is made of the colors of the rainbow mixed together. He explained light as tiny particles moving at high speed. Other scientists, including Christiaan Huygens, showed that reflection and refraction could also be explained by treating light as a wave. At the time, people...

the electromagnetic spectrum

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interference and diffraction

Wave Patterns from Light and Slits

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the bohr model

Bohr’s Quantized Atomic Orbits

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emission spectra

Line Spectra from Heated Gases

Line spectra are produced when heated gases give off light at specific wavelengths. In contrast, hot solids, liquids, or condensed gases radiate excess energy as a continuous spectrum. That spectrum contains an unbroken range of wavelengths. A gas at low partial pressure can produce a line spectrum when it is excited by an electric current or heated. Fluorescent light bulbs and neon signs work in this way. Each element has its own characteristic set of lines, and molecules can also produce...

the de broglie wavelength

Electron Waves and Standing Orbits

Electron waves and standing orbits explain how tiny particles can behave like waves. Large objects in the macroscopic world, like a billiard ball on a table, follow classical physics. A ball keeps moving in a straight line unless it hits another ball or a force such as friction acts on it. It also has a well-defined position, velocity, and momentum, where momentum is mass times velocity. Waves behave differently from macroscopic particles. When waves interact, they can form interference...

the uncertainty principle

Electron Position and Momentum Limits

Heisenberg’s uncertainty principle sets a limit on how precisely we can know an electron’s position and momentum at the same time. Momentum is the motion of a particle, and the two measurements affect each other. If the momentum is known more accurately, the position becomes less certain, and the reverse is also true. Heisenberg described this limit with an equation that uses Planck’s constant. The equation shows the smallest possible uncertainty for position and momentum together. It explains...

the quantum-mechanical model of an atom

Electron Orbitals in Quantum Mechanics

Quantum mechanics explains how electrons behave in atoms using waves and probability. Erwin Schrödinger built on de Broglie’s idea that an electron in hydrogen could act like a circular standing wave instead of moving in fixed circular paths. He then derived the Schrödinger equation, which became a major step in modern atomic theory. When Schrödinger applied his equation to hydrogen-like atoms, it matched Bohr’s energy expression and the Rydberg formula for hydrogen spectra. He described...

quantum numbers

Electron Orbitals and Spin

Electron orbitals are described by quantum numbers that show where an electron is most likely to be found around the nucleus. These numbers come from the quantum mechanical model, which is based on solutions of the Schrödinger equation. They also help explain why electron energy comes in set values instead of changing smoothly. The principal quantum number, n, labels the energy level. It can be 1, 2, 3, and so on, and higher n values usually mean higher electron energy. This number also tells...

atomic orbitals

Electron Regions in Atomic Orbitals

Electron regions in atomic orbitals show where an electron is most likely to be found in an atom. These three-dimensional regions are often drawn as boundary surfaces around the densest part of the cloud. The shape of an orbital depends on the angular momentum quantum number, l. This value can range from 0 to n - 1, where n is the principal quantum number. For n = 1, only l = 0 is allowed. For n = 2, both l = 0 and l = 1 are allowed. Orbitals with the same value of l form a subshell. The l =...

the pauli exclusion principle

Electron Spin and Orbital Pairing

Electron spin and orbital pairing explain why only two electrons can fit in one atomic orbital. Electron configuration describes how electrons are arranged in an atom’s orbitals. It is written with three parts: the principal quantum number, n, the orbital type, or subshell, and a superscript that shows how many electrons are in that subshell. For example, 2p4 means four electrons in a p subshell with n = 2, and 3d8 means eight electrons in a d subshell with n = 3. The three quantum numbers...

the energies of atomic orbitals

Shielding and orbital penetration help explain why electrons in an atom have different energies. Electrons are attracted to the positive nucleus, but they also repel one another in atoms with more than one electron. The strength of these forces depends on the charge and the distance between the particles. Opposite charges attract, like charges repel, and the force gets weaker as the particles move farther apart. An electron that stays closer to the nucleus is held more tightly. That means...

the aufbau principle and hund's rule

Electron Filling Order in Atomic Orbitals

Electron filling order in atomic orbitals follows the aufbau principle and Hund's rule. To write an electron configuration, we build atoms in order of atomic number. Starting with hydrogen and moving across the periods of the periodic table, one proton is added to the nucleus and one electron is placed into the correct subshell. This process describes the ground-state electron configurations of the elements. The aufbau principle comes from the German word aufbau, which means "to build up." It...

electron configuration of multielectron atoms

electron-configuration-of-multielectron-atoms

Valence Electrons and Noble Gas Shorthand

Valence electrons and noble gas shorthand help show how electrons are arranged in multielectron atoms. Sodium, the alkali metal with atomic number 11, has one more electron than neon. That extra electron goes into the lowest-energy subshell available, the 3s orbital, so sodium has the configuration 1s2 2s2 2p6 3s1. Electrons in the outermost shell, where n is highest, are called valence electrons. Electrons in the inner shells are called core electrons. Because core electrons often match a...

key terms and concepts

Learn how shielding, effective nuclear charge, and orbital penetration affect electron energy levels, and why s, p, and d orbitals differ in energy.

Shielding and Orbital Penetration | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

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NC K-12 Science Standard Course of Study

9-12

Matter and its Interactions

PS.Chm.1.3

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Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Atomic structure

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Matter and Its Interactions

CHEM1.PS1.12

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HIgh School

CH.2

CH.2.e

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PS.2

PS.2.a

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CHEM.6.B

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9-12.C.1.1.c

Next Generation Science Standards

HS-PS1-1

Florida Department of Education

SC.912.P.8

SC.912.P.8.5

SC.912.P.10

SC.912.P.10.9

IPC.7.D

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South Carolina College and Career Ready Science Standards

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-7.

Georgia Standards of Excellence

SC1.

electron-configuration-and-chemical-properties

Electron Configuration and Chemical Properties

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IPC.7.A

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The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Melting Points

Melting Points in Organic Chemistry
The melting point of a compound is the temperature at which the solid phase transitions into the liquid phase at a ...

Boiling Points

Source: Lara Al Hariri at the University of Massachusetts Amherst, MA, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation ...

Explain how physical and chemical properties of substances are related to their usage in everyday life such as in sunscreen, cookware, industrial applications, and fuels.

IPC.7.C

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

Metal Flame Emission

Metal Flame Emission
Flame testing is an analytical technique where a sample is placed in a flame, and the characteristic flame color is used to identify ...

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 ...

Explain how electrons can transition from a high energy level to a low energy state, emitting photons at different frequencies for different energy transitions.

Science concepts. The student knows that relationships exist between the structure and properties of matter. The student is expected to:

Shielding and Orbital Penetration

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