Name: molecular shapes from electron pairs
Uploaded: 2025-05-22T09:05:32.000Z
Duration: 2 min 37 s
Channel: JoVE

valence 쉘 전자 쌍 반발, 또는 VSEPR, 이론은 단일 채권에 관련된 전자 그룹, 여러 채권, 또는 외로운 쌍서로 격퇴하고 서로 가능한 최대 거리에 머물려고 가정합니다.
분자 기하학은 중앙 원자 주위에 각종 전자 단의 배열에 의해 지시됩니다.
5개의 기본적인 분자 모양이 있습니다: 2개의 접합 전자 단을 위한 선형, 3개의 삼각형 평면, 4를 위한 테트라헤드랄, 5를 위한 삼각 양성체, 및 6개의 옥타헤드랄.
분자 기하학을 예측하는 동안, 외로운 쌍-외로운 쌍 반발은 외로운 쌍 결합 쌍 및 결합 쌍-결합 쌍 반발 보다 더 큰 기억.
메탄, 암모니아 및 물의 루이스 구조를 고려하십시오. 각각, 중앙 원자는 4개의 전자 단에 의해 포위됩니다.
메탄에서 4개의 접합 전자 쌍은 이상적인 H-C-H 각도109.5°로 테트라헤드방식으로 배열됩니다.
암모니아에서 질소 원자에는 3 개의 결합 쌍과 1 개의 외로운 쌍이 있습니다.
전자의 외로운 쌍은 결합 쌍보다 더 큰 공간을 차지한다. 이것은 외로운 쌍이 단지 1개의 핵에 묶여 있기 때문에, 결합 전자 단은 2개의 핵에 의해 공유되는 반면.
H-N-H 결합 각도는 메탄에서 관찰된 바와 같이 예상 테트라헤드랄 각도인 109.5°보다 작습니다. 본드 각도의 이러한 압축은 인접한 결합 전자 그룹에 외로운 쌍에 의해 가해지는 반발력에 기인한다.
전자 쌍의 배열은 전자 쌍 형상이라고합니다. 분자 형상은 원자의 배열을 설명하고 전자 쌍 형상과 다릅니다. 암모니아용 전자 쌍 기하학은 테트라헤드랄인 반면 분자 형상은 삼각형 피라미드입니다.
물 분자는 또한 중앙 원자의 주위에 4개의 전자 단이 있습니다. 전자 쌍 형상은 또한 두 개의 결합 전자 그룹과 두 개의 외로운 쌍을 가진 테트라 헤드랄입니다.
두 개의 외로운 쌍에 의해 가해지는 더 중대한 반발은 물 분자에 있는 H-O-H 결합 각을 더 압축합니다. 이상적인 테트라헤드랄 결합 각도보다 훨씬 작고 분자 형상이 구부러져 있습니다.

vsepr 이론

원자가 껍질 전자쌍 반발 이론(VSEPR 이론)을 사용하면 루이스 구조의 결합 수와 고독 전자쌍을 조사하여 중심 원자 주변의 분자 구조를 예측할 수 있습니다. VSEPR 모델은 중심 원자의 원자가 껍질에 있는 전자 쌍이 전자 쌍 사이의 거리를 최대화하여 전자 쌍 사이의 반발을 최소화하는 배열을 채택한다고 가정합니다. 중심 원자의 원자가 껍질에 있는 전자는 주로 결합된 원자 사이에 위치하는 결합쌍이나 고립전자쌍을 형성합니다.

분자 내 전자 밀도의 두 영역은 반발을 최소화하기 위해 중심 원자의 반대쪽에 선형으로 배향됩니다. 유사하게, 3개의 전자 그룹은 삼각 평면 기하학적으로 배열되고, 4개의 전자 그룹은 사면체를 형성하고, 5개의 전자 그룹은 삼각 쌍뿔 기하학을 선호하는 반면, 6개의 그러한 그룹은 팔면체 방향으로 배열됩니다.

중심 원자 주변의 전자쌍 기하학적 구조가 분자 구조와 항상 동일하지는 않다는 점에 유의하는 것이 중요합니다. 전자쌍 기하학은 전자가 분자, 결합 및 고립 전자쌍에 위치하는 모든 영역을 설명합니다. 분자 구조는 전자가 아닌 분자 내 원자의 위치를 나타냅니다. 따라서 전자쌍의 기하학적 구조는 중심 원자 주위에 고독한 전자쌍이 없을 때만 분자 구조와 동일합니다.

고립전자쌍은 결합쌍보다 더 큰 공간을 차지합니다. 이는 고립 전자쌍은 단 하나의 핵에만 결합되어 있는 반면, 결합 전자 그룹은 두 개의 핵에 의해 공유되기 때문입니다. 따라서 고독쌍-고립쌍 반발력은 고독쌍-결합쌍 및 결합쌍-결합쌍 반발력보다 더 큽니다.

VSEPR 이론에 따르면, 말단 원자 위치는 선형, 삼각 평면, 사면체 및 팔면체 전자쌍 기하학에서 동일합니다. 따라서 단일 단독 쌍이 모든 위치를 차지할 수 있습니다. 그러나 삼각쌍뿔기하학에서는 두 개의 축 위치가 세 개의 적도 위치와 다릅니다. 여기서 적도 위치는 120° 결합각으로 인해 더 많은 공간을 사용할 수 있으며 더 큰 고립 쌍을 선호합니다. 마찬가지로 두 개의 비공유 전자쌍과 4개의 결합 쌍이 중심 원자 주위에 팔면체로 배열되면 두 비공유 쌍은 180° 떨어져 있어 정사각형 평면 분자 구조가 됩니다.

이 문서는 에서 발췌되었습니다.<a href="https://openstax.org/books/chemistry-2e/pages/7-6-molecular-structure-and-polarity">Openstax, Chemistry 2e, Section 7.6 Molecular Structure and Polarity</a>.

VSEPR 이론

원자가 껍질 전자 쌍 반발 이론 (VSEPR 이론)을 통해 중앙 원자 주변의 분자 구조를 예측할 수 있습니다.

Education

교육

JoVE Core

Organic Chemistry

유기 화학

Unit 1

제1단원

Covalent Bonding and Structure

공유 결합과 구조

KEY TERMS AND CONCEPTS

주요 용어 및 개념

VSEPR Theory

molecular shapes from electron pairs

Molecular shape can be predicted from the way electron pairs arrange around a central atom. Valence shell electron-pair repulsion theory, or VSEPR theory, uses a Lewis structure to count bonding pairs and lone electron pairs. The main idea is simple: electron pairs spread out as far as possible to reduce repulsion.

In a molecule, the valence electrons around the central atom can be bonding pairs or lone pairs. Bonding pairs are found mainly between bonded atoms. Lone pairs stay on one atom and take up more space than bonding pairs because they are held by only one nucleus.

The number of electron groups helps determine the electron-pair geometry. Two regions of electron density arrange in a linear shape. Three electron groups form a trigonal planar geometry, four form a tetrahedron, five prefer a trigonal bipyramidal geometry, and six arrange in an octahedral pattern.

Electron-pair geometry is not always the same as molecular structure. Electron-pair geometry includes both bonds and lone pairs. Molecular structure shows only the positions of the atoms, so the two match only when the central atom has no lone pairs.

Lone pair repulsions are not equal to bonding pair repulsions. Lone pair–lone pair repulsions are strongest. Lone pair–bonding pair repulsions are next, and bonding pair–bonding pair repulsions are weakest.

In some geometries, the terminal positions are equivalent. This is true for linear, trigonal planar, tetrahedral, and octahedral electron-pair geometries, so a lone pair can occupy any one of those positions. In a trigonal bipyramidal geometry, the two axial positions are different from the three equatorial positions. The equatorial position has more space because of the 120° bond angles, so larger lone pairs prefer it.

A square planar molecular structure can also form in an octahedral arrangement. When two lone pairs and four bonding pairs are placed octahedrally around a central atom, the lone pairs sit 180° apart. That arrangement leaves the atoms in a square planar shape.

Molecular Shapes from Electron Pairs

what is organic chemistry?

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...

polar covalent bonds

Electronegativity in Polar Covalent Bonds

Polar covalent bonds form when atoms share electrons unevenly. This happens in covalent bonds between atoms that have similar, but not identical, tendencies to attract electrons. Nonmetal atoms often make these bonds with other nonmetals. Hydrogen gas, H2, is a simple example of a covalent bond between two hydrogen atoms. A covalent bond begins when two atoms move close enough for their valence orbitals to overlap. In hydrogen, the 1s orbitals overlap and the single electrons on each atom...

lewis structures and formal charges

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...

vsepr theory

Molecular shape can be predicted from the way electron pairs arrange around a central atom. Valence shell electron-pair repulsion theory, or VSEPR theory, uses a Lewis structure to count bonding pairs and lone electron pairs. The main idea is simple: electron pairs spread out as far as possible to reduce repulsion. In a molecule, the valence electrons around the central atom can be bonding pairs or lone pairs. Bonding pairs are found mainly between bonded atoms. Lone pairs stay on one atom and...

molecular geometry and dipole moments

Predicting Shape and Molecular Polarity

Molecular shape and molecular polarity can be predicted with VSEPR theory and dipole moments. Start by writing the Lewis structure of the molecule or polyatomic ion. Then count the electron groups around the central atom. Lone pairs and bonds both count as electron groups, and a single, double, or triple bond each counts as one region of electron density. Use that count to identify the electron-pair geometry. Next, use the number of lone pairs to determine the molecular structure. If more than...

resonance and hybrid structures

Resonance in Nitrite and Carbonate Ions

Resonance explains why some Lewis structures do not match the measured properties of a molecule or ion. When two or more Lewis structures have the same atom arrangement, the real electron distribution is an average of the structures shown. The nitrite anion, NO2−, is one example. It can be drawn in two ways, with the N–O and N=O bonds in different places. If nitrite had one single bond and one double bond, the two bond lengths should be different, because a double bond is shorter and stronger...

valence bond theory and hybridized orbitals

valence-bond-theory-and-hybridized-orbitals

Covalent Bond Overlap and Orbital Hybridization

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mo theory and covalent bonding

Bond Order and Molecular Orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found. Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no...

intermolecular forces and physical properties

intermolecular-forces-and-physical-properties

How Intermolecular Forces Affect Matter

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solubility

Why Some Substances Dissolve in Water

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introduction to functional groups

Functional Groups and Organic Molecules

Functional groups are groups of atoms with specific chemical properties that appear within organic molecules. They are sometimes shown as "R." These groups sit along the carbon backbone of macromolecules, which can form chains or rings of carbon atoms. Functional groups help functionalize a compound. That means they can give the molecule different physical and chemical properties. In organic chemistry, this change in group structure can strongly affect how a compound behaves. Common...

overview of advanced functional groups

Advanced Functional Groups in Organic Chemistry

Advanced functional groups are atom clusters in organic molecules that give those molecules specific chemical properties. They are sometimes shown as "R" in formulas. By changing the atoms attached to a carbon skeleton, a functional group can make a compound behave differently in physical and chemical reactions. This topic covers several major classes of organic compounds with advanced functional groups. Aromatic hydrocarbons include benzene. Phenol is another example and is also called...

key terms and concepts

Learn how VSEPR theory uses bonding pairs and lone pairs to predict molecular shape, electron-pair geometry, and common arrangements like linear and octahedral.

Molecular Shapes from Electron Pairs | JoVE K12

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JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Molecular Shapes from Electron Pairs

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