Questions and Answers
Which scientist developed a model that can be used to predict the structure of a molecule?
Which atom has a Lewis structure with an octet?
In a Lewis structure, a dash drawn between two atoms represents _______________.
a shared electron pair
Which of the following atoms would most likely be terminal in a Lewis structure?
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Which of the following descriptions best describes the type of electrons used to write a Lewis structure?
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Which of the following is an exception to the octet rule?
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Which of the following symbols are used to illustrate commonalities between two or more resonance structures?
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How many resonance structures exist for the formate ion, HCO2−?
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Which of these molecules or ions exhibit resonance?
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Construct an orbital diagram to show the electron configuration for a neutral magnesium atom, Mg.
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To form a stable ion, will magnesium gain or lose electrons? How many electrons?
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Match each ion with the noble gas whose electron configuration it shares.
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How many electrons are transferred between the cation and anion to form the ionic bond in one formula unit of each compound?
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Which nonmetals could form an ionic compound with magnesium with the formula MgX2 (where X represents the nonmetal)?
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Use Lewis theory to determine the formula for the compound that forms from Al and S.
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Use Lewis theory to determine the formula for the compound that forms from Na and S.
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Use Lewis theory to determine the formula for the compound that forms from Sr and Se.
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Use Lewis theory to determine the formula for the compound that forms from Ba and F.
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Use the Lewis model to predict the correct formula for the compound that forms between Ca and Br.
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How many total valence electrons are in the Lewis structure of NO3−?
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Determine the electron geometry of N2O (oxygen is terminal).
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Determine the molecular geometry of N2O (oxygen is terminal).
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Determine the electron geometry of SO2.
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Determine the molecular geometry of SO2.
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Determine the electron geometry of H2S.
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Determine the molecular geometry of H2S.
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Determine the electron geometry of PF3.
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Determine the molecular geometry of PF3.
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CO2−3
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ClO−2
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NO−3
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NH+4
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What is the molecular geometry of N2O (Nitrogen is the central atom)?
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What is the molecular geometry of PBr3?
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Which bond is polar?
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Which molecule is polar?
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If a molecule has polar bonds, is the molecule itself polar?
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Why?
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How do you determine the number of electrons that go into the Lewis structure of a molecule?
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What happens if you try to mix a polar liquid with a nonpolar one?
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Use the Lewis model to explain why the compound that forms between hydrogen and sulfur has the formula H2S.
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Would you expect HS to be stable?
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Would you expect H3S to be stable?
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If all of the electron groups around a central atom are bonding groups (that is, there are no lone pairs), what is the molecular geometry for two electron groups?
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If all of the electron groups around a central atom are bonding groups (that is, there are no lone pairs), what is the molecular geometry for three electron groups?
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If all of the electron groups around a central atom are bonding groups (that is, there are no lone pairs), what is the molecular geometry for four electron groups?
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Indicate which of the electrons in the electron configuration are shown in the Lewis structure.
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Indicate which of the electrons in the electron configuration are shown in the Lewis structure.
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Electron groups: 2. Bonding groups: 2. Lone pairs: 0.
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Bonding groups: 3. Lone pairs: 0.
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Bonding groups: 2. Lone pairs: 1.
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Bonding groups: 4. Lone pairs: 0.
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Bonding groups: 3. Lone pairs: 1.
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Bonding groups: 2. Lone pairs: 2.
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How many bonding electrons are in the Lewis structure of N2?
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How many bonding electrons are in the Lewis structure of carbon monoxide, CO?
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How many valence electrons are in the nitrate ion?
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The correct Lewis structure for BF3 would be exactly:
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Which of the following compounds have resonance structures?
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The VSEPR theory predicts that the angle between the central carbon atom and the two oxygen atoms in CO2 measures 180°.
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What is the angle between electron groups in the linear electron geometry?
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When you have 4 electron groups and none of them are lone pairs, the molecular geometry is trigonal pyramidal.
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What is the molecular geometry if you have 4 single bonds around the central atom?
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What is the electron geometry if you have 3 electron groups around the center atom?
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What is the molecular geometry of CCl4?
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The electron geometry and the molecular geometry of ammonia (NH3) are, respectively:
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The elements with the highest electronegativity values tend to be found in the:
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Which molecule listed below has a polar covalent bond?
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Which molecule listed below has a nonpolar covalent bond?
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Which molecule listed below is a polar molecule?
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Which of the following statements are TRUE about the BF3 molecule?
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Consider the following electronegativity values: H = 2.1, Cl = 3.0, F = 4.0. Which molecule below would you expect to have the more polar bond?
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The electronegativity value for Mg is 1.2 and the value for O is 3.5. Based on these values, what type of bond is expected for a compound formed between Mg and O?
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Electronegativity Difference
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CBr4
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H2CO
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CS2
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BH3
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Study Notes
G.N. Lewis and Lewis Structures
- G.N. Lewis developed a model for predicting molecular structures.
- Lewis structures use symbols to represent atoms, with dots for valence electrons.
- A dash between atoms indicates a shared electron pair.
Valence Electrons and Octet Rule
- Valence electrons are the electrons involved in chemical bonding.
- Noble gases typically have a complete octet, contributing to their stability (e.g., Ar has an octet).
- Exceptions to the octet rule include molecules like SF6.
Resonance Structures
- Resonance occurs when more than one valid Lewis structure can be drawn for a molecule.
- The symbol ↔ illustrates shared characteristics between multiple resonance structures.
- The formate ion (HCO2−) has 2 resonance structures.
Electron and Molecular Geometry
- Electron geometry considers bonding and lone pairs around a central atom.
- For two electron groups: linear geometry (180° angle).
- For three electron groups: trigonal planar geometry (120° angle).
- For four electron groups: tetrahedral geometry (109.5° angle).
Bonding and Ions
- Ionic compounds form from the transfer of electrons between metals and nonmetals.
- Magnesium typically loses two electrons to form a stable ion.
- Common ionic compounds include Na2S and BaF2.
- Elements with high electronegativity often form polar bonds, as seen in H2O and HF.
Polar vs. Nonpolar Molecules
- Polar molecules have an uneven distribution of charge due to their molecular structure and bonds.
- Nonpolar molecules, like H2, have an even charge distribution.
- Geometry plays a crucial role in determining whether a molecule is polar or nonpolar.
Molecular Shapes
- Molecular geometry determines physical properties and reactivity.
- Examples of molecular geometries include:
- NH3: Trigonal pyramidal
- H2S: Bent
- CO2: Linear
- CF4: Tetrahedral
Electronegativity and Bonding Types
- Electronegativity differences determine bond types:
- Pure covalent (0-0.4), polar covalent (0.4-2.0), and ionic (2.0+).
- Compounds formed from Mg and O are expected to be ionic due to their significant electronegativity difference.
Summary of Notable Compounds
- Ozone (O3) exhibits resonance structures.
- BF3 is nonpolar with trigonal planar geometry and violates the octet rule.
- The molecule HCN and others like NH3 and H2O are polar due to their structure and electronegativity differences.
Important Concepts in Lewis Structures
- When counting electrons for Lewis structures, sum the valence electrons from all atoms involved.
- Mixing polar and nonpolar liquids results in separation into distinct regions rather than forming a homogenous solution.
- Stable compounds can form despite differing electron configurations, emphasizing understanding of valence electrons and molecular geometries.
VSEPR Theory
- VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular shapes based on repulsion between electron groups.
- Molecules with no lone pairs around a central atom exhibit clear geometric arrangements (linear, trigonal planar, tetrahedral).
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