Chemistry Chapter 13: Structure and Shape

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Questions and Answers

What is the first step in drawing a Lewis diagram?

  • Join atoms by single bonds.
  • Place the least electronegative atom(s) in the center of the molecule or ion.
  • Calculate the total number of valence electrons. (correct)
  • Draw a tentative diagram.

What is the second step in drawing a Lewis diagram?

  • Place the least electronegative atom(s) in the center of the molecule or ion. (correct)
  • Join atoms by single bonds.
  • Calculate the total number of valence electrons.
  • Draw a tentative diagram.

What is the purpose of step 4 in drawing a Lewis diagram?

  • To calculate the number of valence electrons in the tentative diagram.
  • To compare the number of valence electrons in the tentative diagram with the actual number of valence electrons.
  • To remove a lone pair from the central and terminal atoms and replace them with an additional bonding pair.
  • All of the above. (correct)

What is the main goal of this chapter?

<p>To learn about the structure and shape of molecules. (B)</p> Signup and view all the answers

What is the difference between hydrocarbons and other organic compounds?

<p>Hydrocarbons contain only carbon and hydrogen atoms, while other organic compounds contain other atoms as well. (A)</p> Signup and view all the answers

What is the difference between alcohols, ethers, and carboxylic acids?

<p>They differ in the functional group that they contain. (A)</p> Signup and view all the answers

What is the central atom in the hydrogen carbonate ion, HCO3-

<p>Carbon (B)</p> Signup and view all the answers

How many valence electrons are there in the hydrogen carbonate ion, HCO3-

<p>24 (C)</p> Signup and view all the answers

What is the electron-pair geometry for a molecule with 3 regions of electron density surrounding the central atom?

<p>Trigonal planar (D)</p> Signup and view all the answers

What is the total number of electron pairs in the hydrogen carbonate ion, HCO3-

<p>11 (C)</p> Signup and view all the answers

What is the shape of the hydrogen carbonate ion, HCO3-, according to VSEPR theory?

<p>Trigonal planar (D)</p> Signup and view all the answers

What is the bond angle for a molecule with a linear electron-pair geometry?

<p>180° (C)</p> Signup and view all the answers

What is the electron-pair geometry of the hydrogen carbonate ion, HCO3-

<p>Tetrahedral (D)</p> Signup and view all the answers

Which of the following describes the molecular geometry of a molecule with two bonding regions and one lone pair of electrons?

<p>Angular (C)</p> Signup and view all the answers

What is the electron-pair angle in a tetrahedral geometry?

<p>109.5 degrees (D)</p> Signup and view all the answers

What is resonance?

<p>The process of creating a molecule or ion by changing only the positions of the electrons (C)</p> Signup and view all the answers

What is the bond angle for a molecule with a tetrahedral electron-pair geometry?

<p>109.5° (D)</p> Signup and view all the answers

What is the molecular geometry of a molecule with three bonding regions and no lone pairs?

<p>Trigonal planar (B)</p> Signup and view all the answers

What is a resonance hybrid?

<p>The actual molecule or ion that is an average of the resonance structures (D)</p> Signup and view all the answers

What are isomers?

<p>Two compounds having the same molecular formulas but different structures (B)</p> Signup and view all the answers

What type of line is used to represent an atom that is behind the plane of the page in a wedge-and-dash diagram?

<p>Dashed line (D)</p> Signup and view all the answers

What is VSEPR theory?

<p>The idea that electron pairs repel each other (B)</p> Signup and view all the answers

In a wedge-and-dash diagram, what does a wedge-shaped line represent?

<p>An atom in front of the plane of the page (A)</p> Signup and view all the answers

What is the first step in predicting the molecular geometry of a molecule?

<p>Draw the Lewis diagram (A)</p> Signup and view all the answers

What two factors are considered when determining the electron-pair geometry of a molecule?

<p>Number of lone pairs and number of bonding pairs (B)</p> Signup and view all the answers

Which of the following molecules would be considered a polar molecule?

<p>CH2Cl2 (A), CHCl3 (D)</p> Signup and view all the answers

Which of the following is NOT classified as an inorganic compound?

<p>Hydrocarbons (D)</p> Signup and view all the answers

What is the defining characteristic of an alkane?

<p>Each carbon atom forms four single bonds. (B)</p> Signup and view all the answers

Which functional group is characteristic of alcohols?

<p>Hydroxyl group (C)</p> Signup and view all the answers

Which of the following statements accurately describes carboxylic acids?

<p>They are weak acids that only slightly ionize in water. (A)</p> Signup and view all the answers

What is the molecular geometry of a molecule with three regions of electron density, one of which is a lone pair?

<p>Trigonal pyramidal (A)</p> Signup and view all the answers

What is the electron-pair geometry around a central atom with two lone pairs and two bonding regions?

<p>Tetrahedral (A)</p> Signup and view all the answers

Which of the following features can result in a nonpolar molecule?

<p>All bonded atoms are identical (B)</p> Signup and view all the answers

In a wedge-and-dash diagram, what does a dashed line represent?

<p>A bond pointing away from the viewer (D)</p> Signup and view all the answers

What is the molecular geometry of nitrogen trichloride, NCl3?

<p>Trigonal pyramidal (A)</p> Signup and view all the answers

How does a polar molecule behave in an electric field?

<p>It aligns with the more electronegative atoms pointing towards the positive plate (C)</p> Signup and view all the answers

Which of the following molecules will have a linear molecular geometry?

<p>CO2 (D)</p> Signup and view all the answers

What is the electron-pair geometry around the carbon atom in tetrafluoroethylene, C2F4?

<p>Trigonal planar (B)</p> Signup and view all the answers

What is the main factor that determines the electron-pair geometry around a central atom?

<p>The number of regions of electron density around the central atom (C)</p> Signup and view all the answers

Which of the following statements accurately describes a wedge-and-dash diagram?

<p>It shows the arrangement of bonds and lone pairs around the central atom (B)</p> Signup and view all the answers

Flashcards

Lewis Diagram

A representation showing all valence electrons in a molecule or ion.

Electron-Pair Geometry

The spatial arrangement of regions of electron density around a central atom.

Molecular Geometry

The 3D arrangement of atoms in a molecule, determined by electron-pair geometry.

Wedge-and-Dash Diagram

A 2D representation of a molecule that shows 3D connectivity with bonds.

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Polar vs Nonpolar Molecules

Polar molecules have a net dipole moment; nonpolar do not.

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Organic Compounds

Compounds primarily made of carbon, often including hydrogen.

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Inorganic Compounds

Compounds that typically do not contain carbon-hydrogen bonds.

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Valence Electrons

Electrons in the outermost shell of an atom, involved in bonding.

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Central Atom

The atom in a molecule that other atoms bond to, typically less electronegative.

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Resonance Structures

Different Lewis diagrams for the same molecule, differing only in electron positions.

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Resonance Hybrid

A representation of a molecule that is an average of multiple resonance structures.

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Electron-Pair Repulsion

The principle that electron pairs around a central atom repel each other and maximize distance.

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VSEPR Theory

Theory that predicts molecular shapes based on electron pair repulsion.

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Electron-Pair Angle

The angle formed between two electron pairs around a central atom.

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Isomers

Compounds that have the same molecular formula but different structural arrangements.

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Tetrahedron

A geometric shape with four triangular faces, common in molecular geometry.

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Linear Electron-Pair Geometry

Occurs with 2 regions of electron density, bond angle 180°.

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Trigonal Planar Geometry

Occurs with 3 regions of electron density, bond angle 120°.

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Tetrahedral Geometry

Occurs with 4 regions of electron density, bond angle 109.5°.

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Bond Angle

The angle between two adjacent bonds.

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Regions of Electron Density

Represents areas where electrons reside around a central atom (bonds + lone pairs).

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Angular/Bent Molecular Geometry

Occurs when there are 2 bonding and 1 lone pair electron regions.

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Predicting Molecular Geometries

A systematic approach using Lewis diagrams to determine geometry by counting electron density regions.

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Polar molecules

Molecules that have an uneven distribution of charges, resulting from asymmetry around an axis.

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Hydrocarbons

Compounds composed only of hydrogen and carbon atoms; includes alkanes, alkenes, and alkynes.

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Alcohols

Organic compounds that contain a hydroxyl group (-OH) which determines their chemical properties.

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Ethers

Compounds with two hydrocarbon groups bonded to a single oxygen atom.

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Carboxylic Acids

Compounds with a carboxyl group (-COOH), weak acids that ionize partially in water.

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Trigonal Pyramidal

A molecular geometry with three bonding regions and one lone pair.

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Bent Molecular Geometry

A molecular shape with two bonding regions and two lone pairs.

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Conditions for Nonpolarity

Central atom has no lone pairs and all bonded atoms are identical.

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Study Notes

Chapter 13: Structure and Shape

  • This chapter focuses on the structure and shape of molecules and polyatomic ions.

  • Key goals include drawing Lewis diagrams, describing electron-pair geometries, predicting molecular geometries, and drawing wedge-and-dash diagrams.

  • Determining if a molecule is polar or nonpolar and identifying polarity.

  • Distinguishing between organic and inorganic compounds, as well as hydrocarbons and other organic compounds. Differences in structure and geometry for various organic compound classes (alcohols, ethers, carboxylic acids).

  • A step-by-step process is outlined for drawing Lewis diagrams, including calculating valence electrons and ensuring octet completion.

  • Resonance structures are explored, representing equivalent Lewis diagrams where electrons are repositioned.

  • The actual molecule is a 'resonance hybrid,' a blend of the resonance structures. Isomers are also introduced: different molecules with the same molecular formula.

  • Valence Shell Electron Pair Repulsion (VSEPR) theory explains how electron pairs arrange themselves to maximize distance, influencing molecular shapes.

  • Electron-pair angles and specific geometries (linear, trigonal planar, tetrahedral) are presented based on the number of electron-pair regions around the central atom.

  • Tables and figures illustrate various molecular geometries for different numbers of regions of electron density (2, 3, and 4).

  • Wedge-and-dash diagrams are explained for illustrating 3D molecular structures.

  • Steps for predicting molecular geometries based on electron density around the central atom are given

  • Examples and exercises (like ammonia NH3 and hydrogen carbonate HCO3-) are provided to further illustrate the concepts.

  • Differences between organic and inorganic compounds are detailed.

  • Organic chemistry focuses on carbon compounds.

  • Alkane definition: Each carbon atom forms four single bonds.

  • Isomers and their structures (such as butane and pentane isomers) are described.

  • Hydroxyl (-OH), ethers, and carboxylic acids (-COOH) groups are part of specific classes of organic compounds.

  • Differences between alcohols, ethers, and carboxylic acids in terms of their structure and properties are shown.

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