Name: predicting molecular shape with vsepr
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 52 s
Channel: JoVE

K12 Standards

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Ohio’s Learning Standards and Model Curriculum

9-12

Chemistry

Structure And Properties Of Matter

Chemical bonding

VSEPR Theory and the Basic Shapes

Valence shell electron-pair repulsion or VSEPR theory serves as a tool to predict molecular structure.

It assumes that the negatively charged electron groups, which may be electrons involved in a single bond, multiple bonds, or lone pairs, repel one another and try to stay at the maximum possible distance from each other to minimize repulsions.

Imagine a set of balloons tied together. Each balloon orients itself away from the other as much as possible.

Molecular geometry is dictated by the arrangement of various electron groups around the central atom. 

Beryllium fluoride has two electron groups around the central atom. According to VSEPR, the minimum repulsion between these electron groups is achieved through a maximum separation. Thus, the bond angle is 180&#176;, and the molecular shape is linear.

Boron trifluoride has three electron groups around the central boron atom. The repulsion between these groups can be minimized by assuming a 120&#176; bond angle. VSEPR theory predicts that the molecule exhibits trigonal planar geometry.

In the case of methane, there are four electron groups surrounding the central carbon atom. They are farthest when the bond angle is 109.5&#176;, and the molecule ass

vsepr theory and the basic shapes

<h4>Overview of VSEPR Theory</h4>

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure, including approximate bond angles around a central atom, of a molecule from an examination of the number of bonds and lone electron pairs in its Lewis structure. The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between these electron pairs by maximizing the distance between them. The electrons in the valence shell of a central atom form either bonding pairs of electrons, located primarily between bonded atoms, or lone pairs. The electrostatic repulsion of these electrons is reduced when the various regions of high electron density assume positions as far from each other as possible.

VSEPR theory predicts the arrangement of electron pairs around each central atom and, usually, the correct arrangement of atoms in a molecule. We should understand, however, that the theory only considers electron-pair repulsions. Other interactions, such as nuclear-nuclear repulsions and nuclear-electron attractions, are also involved in the final arrangement that atoms adopt in a particular molecular structure.

<h4>Application of VSEPR Theory</h4>

VSEPR theory can be used to predict the structure of molecules. For example, let us predict the structure of a gaseous CO2 molecule. The Lewis structure of CO2 (Figure 1) shows only two electron groups around the central carbon atom. With two bonding groups and no lone pairs of electrons on the central atom, the bonds are as far apart as possible, and the electrostatic repulsion between these regions of high electron density is reduced to a minimum when they are on opposite sides of the central atom. The bond angle is 180&#176;.

<img alt="Carbon dioxide Lewis structure diagram, showing C=O double bonds and electron arrangement." src="/files/core/CDNSource/lessons/1069/1069Image_1.png" style="height: 40px;" data-altupdatedat="1754904545000" data-alt="Carbon dioxide (CO2) Lewis structure, diagram, showing electron sharing and bond formation." />

The table below illustrates electron-pair geometries that minimize the repulsions among regions of high electron density (bonds and/or lone pairs). Two regions of electron density around a central atom in a molecule form a linear geometry; three regions form a trigonal planar geometry; four regions form a tetrahedral geometry; five regions form a trigonal bipyramidal geometry, and six regions form an octahedral geometry.

<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;"> </td>
			<td style="color: black; border: 1px solid black; text-align: center;">BeF2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">BF3</td>
			<td style="color: black; border: 1px solid black; text-align: center;">CH4</td>
			<td style="color: black; border: 1px solid black; text-align: center;">PCl5</td>
			<td style="color: black; border: 1px solid black; text-align: center;">SF6</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Number of electron regions </td>
			<td style="color: black; border: 1px solid black; text-align: center;">2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">3</td>
			<td style="color: black; border: 1px solid black; text-align: center;">4</td>
			<td style="color: black; border: 1px solid black; text-align: center;">5</td>
			<td style="color: black; border: 1px solid black; text-align: center;">6</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Electron region geometry</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Linear; 180&#176; angle</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Trigonal planar; all angles 120&#176;</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Tetrahedral; all angles 109.5&#176;</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Trigonal bipyramidal, angles 90&#176; or 120&#176;.</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Octahedral; all angles 90&#176; or 180&#176;.</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Spatial arrangement</td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Molecular structure diagram, showing linear triatomic molecule with two outer and one central atom." src="/files/core/CDNSource/lessons/1069/1069Image_2.png" style="width: 140px;" data-altupdatedat="1754904545000" data-alt="Ball and stick model of a dioxygen molecule, O2, illustrating molecular structure in chemistry." /></td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Sodium chloride molecule diagram, ball-and-stick model, NaCl structure." src="/files/core/CDNSource/lessons/1069/1069Image_3.png" style="height: 80px;" data-altupdatedat="1754904545000" data-alt="Molecule structure diagram with central atom, bonds, and three peripheral atoms." /></td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Methane molecule diagram, CH&#8324; structural formula, 3D chemical education, molecular geometry." src="/files/core/CDNSource/lessons/1069/1069Image_4.png" style="height: 80px;" data-altupdatedat="1754904545000" data-alt="Molecular structure of methane, CH&#8324;, diagram showing geometry for chemistry education." /></td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Molecular geometry diagram; trigonal bipyramidal arrangement; educational chemistry illustration." src="/files/core/CDNSource/lessons/1069/1069Image_5.png" style="height: 80px;" data-altupdatedat="1754904545000" data-alt="Chemical structure diagram; trigonal bipyramidal molecular geometry, central atom with five bonds." /></td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Molecular structure diagram of sulfur hexafluoride, SF6, octahedral shape, inorganic chemistry." src="/files/core/CDNSource/lessons/1069/1069Image_6.png" style="height: 80px;" data-altupdatedat="1754904545000" data-alt="Molecular structure diagram of octahedral coordination complex, featuring central and peripheral atoms." /></td>
		</tr>
	</tbody>
</table>

Table 1. The basic electron-pair geometries predicted by VSEPR theory maximize the space around any region of electron density (bonds or lone pairs).

This text has been adapted from <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><a href="https://openstax.org/books/chemistry-2e/pages/7-6-molecular-structure-and-polarity">.</a>

Overview of VSEPR Theory

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure, including approximate ...

Education

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Chemical Bonding: Molecular Geometry and Bonding Theories

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KEY TERMS AND CONCEPTS

predicting molecular shape with vsepr

VSEPR theory helps predict molecular shape and approximate bond angles around a central atom. VSEPR stands for valence shell electron-pair repulsion. The model uses the Lewis structure to count bonding pairs and lone pairs in the valence shell of the central atom.

The idea behind the theory is simple. Electron pairs in the valence shell arrange themselves to reduce repulsion by staying as far apart as possible. Bonding pairs are found mainly between bonded atoms, while lone pairs stay on the central atom. This spacing helps explain the arrangement of electron regions in a molecule.

VSEPR theory predicts the arrangement of electron pairs around each central atom and, in many cases, the correct arrangement of atoms in a molecule. It is important to remember that the model only considers electron-pair repulsions. Other forces, such as nuclear-nuclear repulsions and nuclear-electron attractions, also affect the final molecular structure.

The theory can be used to predict specific shapes. For CO2, the Lewis structure shows two electron groups around the central carbon atom. With two bonding groups and no lone pairs, the groups move to opposite sides of the carbon. This gives a linear shape with a 180° bond angle.

The basic electron-pair geometries depend on how many regions of electron density surround the central atom. Two regions give a linear geometry with a 180° angle. Three regions give a trigonal planar geometry with 120° angles, and four regions give a tetrahedral geometry with 109.5° angles.

Five electron regions produce a trigonal bipyramidal geometry with 90° or 120° angles. Six electron regions produce an octahedral geometry with 90° or 180° angles. Examples of these groupings include BeF2, BF3, CH4, PCl5, and SF6. In each case, the arrangement maximizes space around the bonds and lone pairs.

Predicting Molecular Shape with VSEPR

VSEPR theory helps predict molecular shape and approximate bond angles around a central atom. VSEPR stands for valence shell electron-pair repulsion. The model uses the Lewis structure to count bonding pairs and lone pairs in the valence shell of the central atom. The idea behind the theory is simple. Electron pairs in the valence shell arrange themselves to reduce repulsion by staying as far apart as possible. Bonding pairs are found mainly between bonded atoms, while lone pairs stay on the...

vsepr theory and the effect of lone pairs

vsepr-theory-and-the-effect-of-lone-pairs

How Lone Pairs Change Molecular Shape

Lone pairs of electrons can change molecular shape and bond angles. Electron-pair geometry includes every region of electron density around a central atom, while molecular structure shows only where the atoms are located. These two ideas match when the central atom has no lone pairs, but they differ when lone pairs are present. Methane, CH4, is a simple example. It has four bonding pairs around carbon, so both the electron-pair geometry and the molecular structure are tetrahedral. Ammonia,...

predicting molecular geometry

VSEPR Rules for Molecular Shapes

VSEPR theory helps predict electron-pair geometry and molecular shape from a Lewis structure. First, write the Lewis structure of the molecule or polyatomic ion. Then count the electron groups around the central atom. A single, double, or triple bond each counts as one region of electron density. Next, match the number of electron groups to the electron-pair geometry. The main geometries are linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. Then use the number of lone...

molecular shape and polarity

Bond Dipoles and Molecular Polarity

Bond dipoles and molecular polarity explain why some molecules have a charged end and others do not. In a polar covalent bond, atoms with different electronegativities share electrons unevenly. The more electronegative atom pulls electron density toward itself and becomes partially negative, while the other atom becomes partially positive. This separation of charge creates a bond dipole moment. The size of a bond dipole moment is written with the Greek letter mu, or μ. It depends on the size...

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Covalent Bond Strength and Orbital Overlap

Covalent bond strength depends on how atomic orbitals overlap. In valence bond theory, a covalent bond forms when two half-filled orbitals, each with one electron, overlap and the two electrons pair up. The shared electron pair is then attracted to both positively charged nuclei, which holds the atoms together. The amount of overlap affects both bond strength and energy. When atoms are far apart, there is no overlap, so the energy is set to zero by convention. As the atoms move closer, their...

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Atomic Orbital Hybridization and Bond Shapes

Atomic orbital hybridization explains how electron orbitals change shape when atoms form covalent bonds. The wave function, ψ, describes the behavior of electrons in an isolated atom. When atoms bond, their wave functions combine through the linear combination of atomic orbitals, and the new orbitals are called hybrid orbitals. Hybrid orbitals do not exist in isolated atoms. They form only in covalently bonded atoms. Their shapes and directions differ from those of the original atomic orbitals.

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Trigonal Bipyramidal and Octahedral Hybridization

Trigonal bipyramidal and octahedral hybridization explain how atoms form five or six bonding orbitals. These models use valence shell atomic orbitals to match the shape of the molecule. They apply to atoms that have d orbitals in their valence subshells, so they do not apply to atoms in the first or second period. For five bonding orbitals, an atom uses one s orbital, three p orbitals, and one d orbital. This creates five sp3d hybrid orbitals. In phosphorus pentachloride, PCl5, the five P-Cl...

molecular orbital theory i

Bonding and Antibonding Molecular Orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It uses quantum mechanics and wave functions, written as Ψ, to describe electron behavior in a molecule. Like electrons in isolated atoms, electrons in molecules occupy discrete, quantized energy levels. A molecular orbital is the region where a valence electron is likely to be found. It is full when it contains two electrons with opposite spin. Molecular orbitals can be built by combining atomic orbitals through the...

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MO Diagrams, Bond Order, and Mixing

Molecular orbital diagrams show how atomic orbitals combine to make bonding and antibonding orbitals in diatomic molecules. In these diagrams, the atomic orbitals of one atom are placed on the left and the atomic orbitals of the other atom are placed on the right. The molecular orbitals appear in the center. Each horizontal line stands for one orbital, and each orbital can hold two electrons. Dashed lines show which atomic orbitals combine to form each molecular orbital. When atomic orbitals...

key terms and concepts

Learn how VSEPR theory uses Lewis structures to predict molecular shape, bond angles, and electron-pair geometry with clear examples like CO2.

Predicting Molecular Shape with VSEPR | JoVE K12

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HS. Structure and Properties of Matter

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The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Quantum Numbers

It is said that the energy of an electron in an atom is quantized; that is, it can be equal only to certain specific values and can jump from one energy ...

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

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Thomson's e/m Experiment

In a beam of charged particles created by a heated cathode, the particles move at different speeds. However, many applications need a beam with uniform ...

Atomic structure
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Content elaboration: Physical Science included properties and locations of protons, neutrons and electrons, atomic number, mass number, cations and anions, isotopes and the strong nuclear force which holds the nucleus together. In this course, the historical development of the atomic model and the positions of electrons are explored in greater detail. Atomic models are constructed to explain experimental evidence and make predictions. The changes in the atomic model over time exemplify how scientific knowledge changes as new evidence emerges and how technological advancements like electricity extend the boundaries of scientific knowledge. Thompson's study of electrical discharges in cathode-ray tubes led to the discovery of the electron and the development of the plum pudding model of the atom. Rutherford's experiment, in which he bombarded gold foil with a-particles, led to the discovery that most of the atom consists of empty space with a relatively small, positively charged nucleus. Bohr used data from atomic spectra to propose a planetary model of the atom in which electrons orbit the nucleus, like planets around the sun. Later, Schrödinger used the idea that electrons travel in waves to develop a model in which electrons travel randomly in regions of space called orbitals (quantum mechanical model). Based on the quantum mechanical model, it is not possible to predict exactly where electrons are located but there is a region of space surrounding the nucleus in which there is a high probability of finding an electron (electron cloud or orbital). Data from atomic spectra (emission and absorption) gives evidence that electrons can only exist at certain discrete energy levels and not at energies between these levels. Atoms are usually in the ground state where the electrons occupy orbitals with the lowest available energy. However, the atom can become excited when the electrons absorb a photon with the precise amount of energy (indicated by the frequency of the photon) to move to an orbital with higher energy. Any photon without this precise amount of energy will be ignored by the electron. The atom exists in the excited state for a very short amount of time. When an electron drops back down to the lower energy level, it emits a photon that has energy equal to the energy difference between the levels. The amount of energy is indicated by the frequency of the light that is given off and can be measured. Each element has a unique emission and absorption spectrum due to its unique electron configuration and specific electron energy jumps that are possible for that element. Being aware of the quantum mechanical model as the currently accepted model for the atom is important for science literacy as it explains and predicts subatomic interactions, but details should be reserved for more advanced study. Electron energy levels consist of sublevels (s, p, d and f), each with a characteristic number and shape of orbitals. Orbital diagrams and electron configuration can be constructed to show the location of the electrons in an atom using established rules. Valence electrons are responsible for most of the chemical properties of elements. In this course, electron configuration (extended and noble gas notation) and orbital diagrams can be shown for any element in the first three periods. Although the quantum mechanical model of the atom explains the most experimental evidence, other models can still be helpful. Thinking of atoms as indivisible spheres is useful in explaining many physical properties of substances, such as the state (solid, liquid or gas) of a substance at room temperature. Bohr's planetary model is useful to explain and predict periodic trends in the properties of elements.

Atomic structure

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 ...

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 ...

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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

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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 ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Periodic Table
• Properties
• Trends

Content elaboration: In the Physical Science course, the concept that elements are placed in order of increasing atomic number in the periodic table such that elements with similar properties are placed in the same column is introduced. How the periodic table is divided into groups, families, periods, metals, nonmetals and metalloids is also included and will be revisited here. In this course, with more information about the electron configuration of elements, similarities in the configuration of the valence electrons for a particular group can be observed. The electron configuration of an atom can be determined from the position on the periodic table. The repeating pattern in the electron configuration for elements on the periodic table explains many of the trends in the properties observed. Atomic theory is used to describe and explain trends in properties across periods or down columns including atomic radii, ionic radii, first ionization energies, electronegativities and whether the element is a solid or gas at room temperature. Additional ionization energies, electron affinities and periodic properties of the transition elements, and the lanthanide and actinide series are reserved for more advanced study.

Periodic Table

Types of Chemical Bonds

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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 ...

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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 ...

Electronegativity

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Electronegativity values of ...

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Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

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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

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Formal Charges

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Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

VSEPR Theory and the Effect of Lone Pairs

Effect of Lone Pairs of Electrons&nbsp;on Molecule Geometry

It is important to note that electron-pair geometry around a central atom is not the same ...

Predicting Molecular Geometry

VSEPR Theory for Determination of Electron Pair Geometries

The following procedure uses VSEPR theory to determine the electron pair geometries and the ...

Molecular Shape and Polarity

Dipole Moment of a Molecule

Polar covalent bonds connect two atoms with differing electronegativities, leaving one atom with a partial positive charge ...

Valence Bond Theory

Overview of Valence Bond Theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single ...

Hybridization of Atomic Orbitals I

The mathematical expression known as the wave function, &#x3C8;, contains information about each orbital and the wavelike properties of electrons in an ...

Hybridization of Atomic Orbitals II

sp3d and sp3d&nbsp;2 Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell ...

Molecular Orbital Theory I

Overview of Molecular Orbital Theory

Molecular orbital theory describes the distribution of electrons in molecules in the same way as the distribution of ...

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams

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Bonding in Metals

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Chemical bonding
• lonic
• Polar/covalent

Content elaboration: Content in the Physical Science course included recognizing that atoms with unpaired electrons tend to form ionic and covalent bonds with other atoms, forming molecules, ionic lattices or network covalent structures. In this course, electron configuration, electronegativity values and energy considerations will be applied to bonding and the properties of materials with different types of bonding. Atoms of many elements are more stable when they are bonded to other atoms. In such cases, as atoms bond, energy is released to the surroundings, resulting in a system with lower energy. An atom's electron configuration, particularly the valence electrons, determines how an atom interacts with other atoms. Molecules, ionic lattices and network covalent structures have different, yet predictable, properties that depend on the identity of the elements and the types of bonds formed. Differences in electronegativity values can be used to predict where a bond fits on the continuum between ionic and covalent bonds. The polarity of a bond depends on the electronegativity difference and the distance between the atoms (bond length). Polar covalent bonds are introduced as an intermediary between ionic and pure covalent bonds. The concept of metallic bonding is also introduced to explain many of the properties of metals (e.g., conductivity). Since most compounds contain multiple bonds, a substance may contain more than one type of bond. Carbon atoms can bond together and with other atoms, especially hydrogen, oxygen, nitrogen and sulfur, to form chains, rings and branching networks that are present in a variety of important compounds, including synthetic polymers, fossil fuels and the large molecules essential to life.

Chemical Formulas

A chemical formula presents information about the proportions of atoms constituting a particular chemical compound or molecule, mainly using symbols of ...

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Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

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Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

Organic Compounds

All living things are formed mostly of carbon compounds called organic compounds. The category of organic compounds includes both natural and synthetic ...

Classification of Elements and Compounds

Pure substances consist of only one type of matter. A pure substance can be an element or a compound. An element consists of only one type of atom, while ...

Molecular Models

Physical models representing molecular architectures of chemical compounds play essential roles in understanding chemistry. The use of molecular models ...

Representing compounds
• Formula writing
• Nomenclature
• Models and shapes (Lewis structures, ball and stick, molecular geometries)

Content elaboration: Using the periodic table, formulas of ionic compounds containing specific elements can be predicted. This can include ionic compounds made up of elements from groups 1, 2, 17, hydrogen, oxygen and polyatomic ions (given the formula and charge of the polyatomic ion). Given the formula, a compound can be named using conventional systems that include Greek prefixes and Roman numerals where appropriate. Given the name of an ionic or covalent substance, formulas can be written. Many different models can be used to represent compounds including chemical formulas, Lewis structures, and ball and stick models. These models can be used to visualize atoms and molecules and to predict the properties of substances. Each type of representation provides unique information about the compound. Different representations are better suited for particular substances. Lewis structures can be drawn to represent covalent compounds using a simple set of rules and can be combined with valence shell electron pair repulsion (VSEPR) theory to predict the three-dimensional electron pair and molecular geometry of compounds. Lewis structures and molecular geometries will only be constructed for the following combination of elements: hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and the halogens.

Measurement: Standard Units

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Measurement: Derived Units

The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, ...

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Uncertainty in Measurement: Accuracy and Precision

Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accuracy ...

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Uncertainty in Measurement: Reading Instruments

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such ...

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Uncertainty in Measurement: Significant Figures

All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a ...

Dimensional Analysis

Dimensional analysis, also known as the factor label method, is a versatile approach for mathematical operations. The main principle behind this approach ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Quantifying matter

Content elaboration: In earlier grades, properties of materials were quantified with measurements that were always associated with some error. In this course, scientific protocols for quantifying the properties of matter accurately and precisely are studied. Using the International System of Units (SI), significant digits or figures, scientific notation, error analysis and dimensional analysis are vital to scientific communication. There are three domains of magnitude in size and time: the macroscopic (human) domain, the cosmic domain and the submicroscopic (atomic and subatomic) domain. Measurements in the cosmic domain and submicroscopic domains require complex instruments and/or procedures. Matter can be quantified in a way that macroscopic properties such as mass can reflect the number of particles present. Elemental samples are a mixture of several isotopes with different masses. The atomic mass of an element is calculated given the mass and relative abundance of each isotope of the element as it exists in nature. Because the mass of an atom is very small, the mole is used to translate between the atomic and macroscopic levels. A mole is equal to the number of atoms in exactly 12 grams of the isotope carbon-12. The mass of one mole of a substance is equal to its molar mass in grams. The molar mass for a substance can be used in conjunction with Avogadro's number and the density of a substance to convert between mass, moles, volume and number of particles of a sample.

Quantifying matter

Predicting Molecular Shape with VSEPR

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