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

المدارات الذرية لها طاقات مختلفة،كما تم تفسيرها من خلال تفاعلات كولوم،تأثير التدريع والاختراق المداري. يشير قانون كولوم إلى أن قوى الجذب والطرد بين جسيمين مشحونين،لها علاقة مربعة عكسية مع المسافة بينهما. تزداد أحجام المدارات الذرية مع زيادة رقم الغلاف،ويتم طرد الإلكترونات من الفضاء المشغول بواسطة المدارات ذات الغلاف الأقل.وهكذا،فإن قانون كولوم يقترح أنّبازدياد رقم الغلاف،الإلكترونات تواجه أقل جاذبية للنواة،والتي تتوافق مع طاقات المدارات الأعلى. بالإضافة إلى ذلك،فإنّالإلكترونات الموجودة على نفس المسافة تقريبًا،من أو أقرب إلى النواة،لها تأثير تدريع مما يقلل من الانجذاب إلى النواة. كلما زاد التدريع،قل الانجذاب إلى النواة.هذا هو أحد أسباب الاختلافات في الطاقات المدارية داخل أغلفة الإلكترون. على سبيل المثال،إلكترونات 3s و 3p تعمل بشكل ملحوظ كدرع لإلكترونات 3d. الشحنة النووية الفعالة التي يشعر بها الإلكترون يتم حسابها عن طريق طرح ثابت التدريع S،والتي تعتمد على عدد إلكترونات التدريع،والأغلفة الفرعية التي يشغلونها،من العدد الذري.على سبيل المثال،الإلكترونان في 1s للليثيوم،الذي عدده الذري ثلاثة،تغطي إلكترون 2s الخاص به. ثابت التدريع لذلك الإلكترون،تم تحديده من القواعد شبه التجريبية ليكون 1.7. ومن ثم،فإن الشحنة النووية الفعالة،التي يشعر بها الإلكترون الثاني هي 1.3.إنّأشكال المدارات تملي طاقتها. إذا كانت الإلكترونات في مدار خارجي يمكن أن تتحرك بعيدًا في المناطق التي تحتلها الإلكترونات الداخلية ليكونوا قريبين من النواة تكون أقل حماية هناك. وبالتالي،فإن طاقة هذا المدار الخارجي أقل.يمكن تصور ذلك،بدالة توزيع شعاعي تصف احتمالية إيجاد إلكترون عند مسافة معينه من النواة. دالة التوزيع الشعاعي للأغلفة الفرعية 1s،2s و 2p تكشف أن إلكترونات 2s لديها احتمال قليل بالتواجد بالقرب من النواة،بينما تبقى إلكترونات 2p في الغالب بالخارج،أو عند الحافة الخارجية من منطقة 1s. وبالتالي،يُقال عن مدار 2s أنه يحصل على قدرة اختراق أكبر.في الغلاف الثالث،إلكترونات 3s الأكثر إختراقاًو إلكترونات 3d الاقل اختراقاًبشكل عام،تزداد الطاقة المدارية الذرية مع زيادة رقم الغلاف،وعلى المستوى الفرعي،من s إلى f. ومع ذلك،يصبح تأثير الاختراق واضح جدا في الأغلفة الرابعة والخامسة،حتى أن المدارات s4 و s5 في كثير من الأحيان لديها طاقة نسبية أقل من المدارات 3d و 4d،على التوالي.

طاقات المدارات الذرّية

في الذرة، تنجذب الإلكترونات سالبة الشحنة إلى النواة الموجبة الشحنة. في الذرة متعددة الإلكترونات، تتم أيضًا ملاحظة عمليات سحب الإلكترون-الإلكترون. إن القوى الجذابة والسحارة معتمدة على المسافة بين الجسيمات، فضلاً عن إشارة الشحنات على الجسيمات الفردية وحجمها. عندما تكون الشحنات على الجسيمات معاكسة، فإنها تجذب بعضها البعض. إذا كان لكل من الجزئيات نفس الشحنة، فإنها تتنافر مع بعضها البعض. ومع تزايد حجم الشحنات، يزداد حجم القوة. ولكن عندما يكون فصل الشحنات أكثر، ينخفض مستوى القوة. وبالتالي، فإن قوة الجذب بين الإلكترون ونواة الذرة تتناسب بشكل طردي مع المسافة بينهما. إذا كان الإلكترون أقرب إلى النواة، فإنه يرتبط بشكل أكثر إحكاماً بالنواة؛ وبالتالي فإن الإلكترونات الموجودة في الحاويات المختلفة (على مسافات مختلفة) لها طاقات مختلفة. بالنسبة إلى الذرات ذات مستويات الطاقة المتعددة، تقوم الإلكترونات الداخلية بحمايتها جزئياً من سحب النواة، نتيجة لتنافرات الإلكترون-الإلكترون. تعمل الإلكترونات الأساسية على حماية الإلكترونات في الحاويات الخارجية، بينما لا تمنع الإلكترونات الموجودة في نفس حاوية التكافؤ الجاذبية النووية التي يجرها بعضها البعض بكفاءة. وبوسعنا أن نفسر هذا بمفهوم الشحن النووي الفعّال، em>Zeff. هذا الجذب الذي يتم بذله على إلكترون معين بواسطة النواة، مع الأخذ في الاعتبار أي عمليات تنافر إلكترون-إلكترون. في حالة الهيدروجين، فلا يوجد سوى إلكترون واحد، وعلى هذا فإن الشحنة النووية (Z) والشحنة النووية الفعّالة (Zeff) متساويتان. بالنسبة لجميع الذرات الأخرى، تقوم الإلكترونات الداخلية بحمايتها جزئياً من جذب النواة، وبالتالي: <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/985/985_Equations-01.png" style="height: 40px;" />يصف الاختراق المداري قدرة الإلكترون على الاقتراب من النواة. يمكن أن تقترب الإلكترونات الموجودة في s-المدار من النواة وأن تكون لها قدرة  أكثر على الاختراق. كثافة الاحتمال لـ s-مدار كروي ليست صفراً في النواة. تختلف الاتجاهات المكانية بـ  اختلاف الحاويات الفرعية. وبسبب المستوى الذي يتخذ شكل الدمبل، يخترق p-إلكترون بشكل أقل بكثير. يحتوي التموّج على عقدة تمر عبر النواة، حيث يكون احتمال العثور على الإلكترون صفراً. وبالتالي، فإن الإلكترون المداري s يرتبط بشكل أكثر إحكاماً بالنواة وله طاقة أقل من p-الإلكترون. حتى أن d-الإلكترون لديه قدرة اختراق أقل وطاقة أعلى منالإلكترون المداري p. بالنسبة للقِشر والقشر الفرعية المختلفة، يمكن تصوير اتجاه قوة الالكترونات المخترِقة كما يلي <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/985/985_Equations-02.png" style="height: 40px;" />يكون تأثير التدريع والاختراق كبيراً، وقد يكون للإلكترونات 4s طاقة أقل من الإلكترونات 3d.تم اقتباس هذا النص من  <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>

في الذرة ، تنجذب الإلكترونات سالبة الشحنة إلى النواة الموجبة الشحنة. في ذرة متعددة الإلكترونات ، تكون تنافر الإلكترون والإلكترون ...

Education

JoVE Core

Chemistry

الكيمياء

واحد

Electronic Structure of Atoms

البنية الإلكترونية للذرات

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

Electromagnetic Waves: Uses Across the Spectrum

The electromagnetic spectrum includes all electromagnetic radiation arranged by frequency and wavelength. Visible light is only a small part of it, and each color of visible light has its own frequency and wavelength. Different parts of the spectrum also use different units. Radio waves are usually measured in MHz, while the visible range is often measured in nm or angstroms. The spectrum is organized from radio waves to gamma rays as frequency increases and wavelength decreases. Radio waves...

interference and diffraction

Wave Patterns from Light and Slits

Light can form wave patterns through interference and diffraction. When two electromagnetic waves meet with their peaks and troughs lined up, they combine into a larger wave. This is constructive interference, and the waves are in phase. When a peak of one wave meets a trough of the other, the waves reduce each other. This is destructive interference, and the result has a much lower amplitude. Diffraction is another wave behavior. When light passes through a slit that is about the same size as...

photoelectric effect

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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

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the uncertainty principle

Electron Position and Momentum Limits

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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

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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

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.12

Virginia  Standards of Learning

HIgh School

CH.2

CH.2.e

Physical Science

PS.2

PS.2.a

CHEM.6

CHEM.6.B

Alabama Course of Study Science

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

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS1-4

new-york-state-science-learning-standards

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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Physical and Chemical Properties of Matter

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Physical Properties of Matter

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IPC.7.B

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Classifying Matter by Composition

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IPC.7.C

Emission Spectra

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

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Shielding and Orbital Penetration

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