Name: predicting shape and molecular polarity
Uploaded: 2023-04-30T18:28:31.000Z
Duration: 2 min 36 s
Channel: JoVE

VSEPR 이론은 전자 쌍 형상 및 분자 형상을 결정하는 데 도움이됩니다.
일련의 단계는 인 트리클로라이드와 같은 분자의 기하학과 결합 각도를 예측하는 데 사용됩니다.
첫 번째 단계는 분자의 루이스 구조를 그리는 것입니다.
다음으로, 중앙 원자에 전자 그룹의 총 수를 계산합니다. 인 주위에는 4개의 전자 단이 있습니다: 3개의 결합 쌍 및 1개의 외로운 쌍.
이제 전자 쌍 형상을 결정합니다. 전자 쌍 형상은 테트라헤드랄입니다. 그러나, 외로운 쌍 때문에, 분자 기하학은 삼각형 피라미드입니다. 외로운 쌍은 본드 각도를 109.5 ° 미만으로 줄입니다.
접합 전자 쌍은 항상 두 접합 원자 사이에 동등하게 공유되지 않습니다.
수력 불소산과 같은 공유 결합에서 전자는 부분 전하로 표시된 더 전기 음수 원자쪽으로 당겨져 있습니다. 이러한 채권은 극지 채권이라고합니다.
전하 분리는 그리스 문자 μ표시된 본드 이폴 순간이라는 벡터를 만듭니다. 그 값은 부분 충전의 크기와 그들 사이의 거리의 제품입니다.
딜레폴 의 순간은 일반적으로 디비로 표현됩니다. 하나의 debye는 3.336 × 10-30 쿨롬 미터와 동일합니다.
벡터는 더 적은 에서 더 많은 전기 음성 원자로 가리키며 결합 이폴 모멘티브를 나타냅니다. 그 길이는 두 원자 사이의 전기성 차이의 크기에 비례한다. 다른 원소의 원자를 포함하는 대부분의 다원자 분자는 편극 순간을 가지고 있으며, 따라서 극성 분자입니다.
다원화합물에서, 그물 이폴 모멘트는 화합물의 개별 결합 이폴 순간 및 기하학에 의해 결정된다.
두 개의 극성 결합을 가진 물 분자를 고려하십시오. 그것은 구부러진 모양을 가지고 있으며 극성 분자입니다.
대조적으로, 이산화탄소 분자는 선형입니다. 두 탄소 - 산소 결합은 극성이지만 반대 방향으로 지향되어 서로의 이폴 순간을 취소하고 전체 분자를 비극성으로 만듭니다.

분자 기하학과 쌍극자 모멘트

VSEPR 이론은 다음과 같이 전자쌍 기하학과 분자 구조를 결정하는 데 사용될 수 있습니다.

<ol style="display: flex; flex-direction: column; gap: 10px;">
<li>-분자나 다원자 이온의 루이스 구조를 쓰세요.</li>

<li>-중심 원자 주변의 전자 그룹(고독전자쌍과 결합)의 수를 셉니다. 단일, 이중 또는 삼중 결합은 전자 밀도의 한 영역으로 간주됩니다.</li>

<li>-전자 그룹의 수를 기준으로 전자쌍의 기하학적 구조를 식별합니다.</li>

<li>-분자 구조를 결정하려면 고립쌍의 수를 사용하십시오. 고립전자쌍과 화학결합의 배열이 두 개 이상 가능하다면 반발력을 최소화하는 배열을 선택하세요.</li>
</ol>

분자의 쌍극자 모멘트

전기음성도가 다른 원자가 결합을 형성하면 전자는 전기음성도가 더 높은 원자 쪽으로 끌려가서 한 원자는 부분 양전하(δ+)를 띠고 다른 원자는 부분 음전하(δ-)를 띠게 됩니다. 이러한 결합을 극성 공유 결합이라고 하며, 전하의 분리로 인해 결합 쌍극자 모멘트가 발생합니다. 결합 쌍극자 모멘트의 크기는 그리스 문자 µ로 표시되며 다음과 같이 주어집니다.

μ = QR

여기서 Q는 부분 전하의 크기(전기 음성도 차이로 결정됨)이고 r은 이들 사이의 거리입니다. 쌍극자 모멘트는 일반적으로 디바이로 표현되며, 여기서 1디바이는 3.336 × 10-30C·m와 같습니다.

결합 쌍극자 모멘트는 전기음성도가 낮은 원자부터 전기음성도가 높은 원자 방향으로 결합을 가리키는 화살표로 표시되는 벡터이며, 전기음성도가 낮은 쪽 끝에는 작은 더하기 기호가 표시됩니다.

전체 분자는 분자 구조와 각 결합의 극성에 따라 전하 분리를 가질 수도 있습니다. 이러한 분자를 극성이라고 합니다. 쌍극자 모멘트는 분자 전체의 순 전하 분리 정도를 측정합니다. 이원자 분자에서는 결합 쌍극자 모멘트가 분자 극성을 결정합니다.

분자가 둘 이상의 결합을 포함하는 경우 기하학적 구조를 고려해야 합니다. 분자의 결합이 결합 모멘트의 벡터 합이 0이 되도록 배열되면 분자는 비극성입니다(예: CO2). 물 분자는 구부러진 분자 구조를 가지고 있으며 두 결합 모멘트는 상쇄되지 않습니다. 따라서 물은 순 쌍극자 모멘트를 갖는 극성 분자입니다.

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 이론은 다음과 같이 전자쌍 형상 및 분자 구조를 결정하는 데 사용할 수 있습니다.

분자의 루이스 구조를 쓰거나 ...

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

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 one arrangement of lone pairs and bonds is possible, choose the one with the fewest repulsions. This step helps show how atoms arrange themselves in space.

Bond polarity depends on electronegativity, which is how strongly an atom pulls shared electrons. When atoms with different electronegativities form a bond, the electrons are pulled toward the more electronegative atom. That leaves one atom with a partial positive charge, written as δ+, and the other with a partial negative charge, written as δ−. These are polar covalent bonds.

The charge separation in a polar bond creates a bond dipole moment. Its magnitude is written with the Greek letter μ and follows the relation μ = Qr, where Q is the size of the partial charges and r is the distance between them. Dipole moments are usually measured in debyes. One debye equals 3.336 × 10^−30 C·m. A bond dipole is shown as an arrow pointing from the less electronegative atom toward the more electronegative atom, with a small plus sign on the less electronegative end.

A whole molecule can also have a dipole moment. That depends on both the polarity of its bonds and its molecular shape. In diatomic molecules, the bond dipole determines the molecular polarity. In molecules with more than one bond, the bond dipoles must be added as vectors. If the vector sum is zero, the molecule is nonpolar, as in CO2. Water has a bent molecular structure, so its bond moments do not cancel. As a result, water is a polar molecule with a net dipole moment.

Predicting Shape and Molecular Polarity

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 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...

molecular geometry and dipole moments

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...

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Resonance in Nitrite and Carbonate Ions

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intermolecular forces and physical properties

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How Intermolecular Forces Affect Matter

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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 VSEPR theory predicts molecular shape, how bond polarity forms, and why some molecules like CO2 are nonpolar while water is polar.

Predicting Shape and Molecular Polarity | JoVE K12

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Predicting Shape and Molecular Polarity

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