Chemistry Chapter 9 & 10: Chemical Bonding
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Questions and Answers

What factor primarily causes lone pairs to compress the angles between bonding pairs in a molecule?

  • Bonding pair dominance
  • Hybridization effects
  • Electron-electron repulsion (correct)
  • Nuclear attraction

Which type of molecular species includes O2, F2, and OF?

  • Hetero Nuclear Diatomic Species (correct)
  • Radical Species
  • Homo Nuclear Diatomic Species
  • Triatomic Species

How is the Bond Order (B.O.) calculated?

  • # of bonding e's - # of antibonding e's / 2 (correct)
  • # of bonding e's + # of lone pairs
  • # of antibonding e's + # of bonding e's
  • # of bonding e's / # of antibonding e's

Which of the following correctly identifies the bond length relation in relation to bond order?

<p>Higher bond order leads to shorter bond lengths (D)</p> Signup and view all the answers

What is the Bond Order of the ion O2-?

<p>1.5 (A)</p> Signup and view all the answers

What characteristic describes species such as B2, C2, and N2?

<p>They are homo nuclear diatomic species. (B)</p> Signup and view all the answers

Which statement is true regarding the dipole moments of molecules with a bond order of 0?

<p>They possess no dipole moment. (C)</p> Signup and view all the answers

Which interaction primarily influences the stability and length of bonds in diatomic molecules?

<p>Covalent sharing of electrons (C)</p> Signup and view all the answers

What is the significance of the octet rule in Lewis structures?

<p>It ensures all atoms have 8 electrons surrounding them. (B), It applies only to hydrogen which should have 2 electrons. (C)</p> Signup and view all the answers

How is the formal charge calculated for an atom within a Lewis structure?

<p>Group number - Number of valence electrons assigned to the atom. (A)</p> Signup and view all the answers

Which atom in a molecule typically carries the negative charge?

<p>The one with the highest electronegativity. (C)</p> Signup and view all the answers

Why do lone pairs of electrons require more space than bonding pairs?

<p>Lone pairs are subject to electron-electron repulsion. (C)</p> Signup and view all the answers

What role do resonance structures play in understanding molecular bonding?

<p>They demonstrate the different ways electrons can be arranged. (A)</p> Signup and view all the answers

In the context of Lewis structures, what does 'AX3' generally represent?

<p>A central atom bonded to three terminal atoms. (D)</p> Signup and view all the answers

What is the bond order for the N-O bond in the molecule NO2 based on the resonance structures?

<p>1.5 (B)</p> Signup and view all the answers

Which of the following statements about Lewis structures is true?

<p>Only valence electrons are shown. (B)</p> Signup and view all the answers

What is the bond order for the N-O bond in NO2?

<p>2 (A)</p> Signup and view all the answers

Which of the following statements is true regarding the N-O bond in NO3?

<p>It has a bond order of 1.33. (D)</p> Signup and view all the answers

How is the number of π bonds determined when a central atom is P, S, Cl, or elements in the 3rd row or beyond?

<p>It equals the number of terminal oxygen atoms plus the charge. (A)</p> Signup and view all the answers

What is the reason a central atom should typically have a formal charge of zero in Lewis structures?

<p>To achieve balance in overall charge. (D)</p> Signup and view all the answers

What is the impact of lone pairs on bond angles in Lewis structures?

<p>They compress the angles between bonding pairs. (D)</p> Signup and view all the answers

Which statement accurately reflects the rules of drawing a Lewis structure regarding valence electrons?

<p>Only the valence electrons are included. (A)</p> Signup and view all the answers

In a molecule containing a terminal F atom, what is true regarding π bonds?

<p>F cannot form any π bonds. (C)</p> Signup and view all the answers

When drawing a Lewis structure for a molecule, what should be the surrounding electron count for terminal atoms?

<p>8 electrons except for hydrogen. (C)</p> Signup and view all the answers

What is the primary requirement for the formation of a stable molecule?

<p>Atoms must achieve noble gas electron configurations. (C)</p> Signup and view all the answers

Which elements are expected to strictly obey the octet rule without exceeding it?

<p>C, N, O, F (A)</p> Signup and view all the answers

Which statement about lone pairs and bonding pairs is true?

<p>Lone pairs require more room than bonding pairs. (D)</p> Signup and view all the answers

What is the formula for calculating Formal Charge (F.C.)?

<p>F.C. = Group number - # of V e's assigned to the atom (B)</p> Signup and view all the answers

For a compound to be polar, what condition must be met regarding its dipole moment?

<p>The dipole moment must be different from zero. (B)</p> Signup and view all the answers

What happens to bond length and bond strength as bond order increases?

<p>Bond length decreases while bond strength increases. (B)</p> Signup and view all the answers

Which rule applies regarding terminal atoms in Lewis structures?

<p>Terminal atoms should obey the octet rule, except Hydrogen which requires 2 electrons. (A)</p> Signup and view all the answers

In VSEPR theory, what configuration minimizes electron-electron repulsion?

<p>Both 120 degrees and 180 degrees minimize repulsion. (B)</p> Signup and view all the answers

What is the geometry of a molecule with the formula AX4?

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

Which of the following species will typically have a non-zero dipole moment?

<p>NCl3 (A), SCl2 (B)</p> Signup and view all the answers

In which circumstance will the formal charge of a central atom be zero?

<p>When the sum of valence electrons assigned equals the group number (A)</p> Signup and view all the answers

Which of the following molecular shapes is not linear?

<p>NCl3 (D)</p> Signup and view all the answers

The electron repulsion is maximum in which position of two electron pairs?

<p>90 degrees (B)</p> Signup and view all the answers

Which of the following arrangements would most likely lead to a zero dipole moment?

<p>AX3 (A), AX4E2 (C)</p> Signup and view all the answers

For the molecule with the formula AX2E2, how many total valence electrons are typically present if A is in group 14 of the periodic table?

<p>18 (B)</p> Signup and view all the answers

Which of the following statements is true about the VSEPR theory?

<p>It predicts molecular shapes based on bonding and non-bonding electron pairs. (A)</p> Signup and view all the answers

What is the maximum number of bonds that hydrogen can form?

<p>One sigma bond (A)</p> Signup and view all the answers

Which of the following atoms can exceed the octet rule?

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

Which hybridization corresponds to a linear molecular geometry with 2 bonding pairs and 0 lone pairs?

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

Which of the following molecular shapes corresponds to an AX3E system?

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

What type of bond can carbon typically form?

<p>Both sigma and pi bonds (B)</p> Signup and view all the answers

Which molecular geometry is predicted for an AX4 molecule with no lone pairs?

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

What is a characteristic feature of fluorine in molecular structures?

<p>Requires 8 electrons around it (D)</p> Signup and view all the answers

In a Lewis structure, what does a dot represent?

<p>A valence electron (C)</p> Signup and view all the answers

Which of the following is true about bromine in molecular structures?

<p>Can be a central atom (B)</p> Signup and view all the answers

In a molecule with the notation AX5, what will its molecular geometry be?

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

If an atom is in the same group as another but is in a lower row, which one should be the central atom?

<p>The one with a larger atomic radius (D)</p> Signup and view all the answers

For the molecular geometry with the notation AX2E2, what shape does the molecule adopt?

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

What is the molecular angle associated with a tetrahedral geometry?

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

Flashcards

Octet Rule

Atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with eight valence electrons, similar to the noble gases.

Lewis Structure

A diagram showing the arrangement of valence electrons around atoms in a molecule or ion, representing bonds and lone pairs.

Formal Charge

The charge an atom would have if all bonding electrons were shared equally.

Valence Shell Electron Pair Repulsion (VSEPR) Theory

Predicts the three-dimensional shape of molecules based on the repulsion between electron pairs in the valence shell.

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Lone Pair

A pair of valence electrons not involved in bonding.

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Bond Order

The number of chemical bonds between two atoms.

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Bond Length

The average distance between the nuclei of two bonded atoms.

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Bond Strength

The energy required to break a bond.

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Central Atom

The atom in a molecule that is bonded to the most other atoms.

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Terminal Atom

An atom in a molecule that is bonded to only one other atom.

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Electronegativity

The tendency of an atom to attract electrons to itself in a chemical bond.

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Resonance Structure

Multiple Lewis structures that contribute to the true electron distribution of a molecule.

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Pi (Ï€) Bonds

A type of covalent bond formed by the sideways overlap of atomic orbitals. They are weaker and less localized than sigma bonds.

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Lone Pair Effect

Lone pairs of electrons, due to electron-electron repulsion, require more space than bonding pairs. This pushes bonding pairs closer together, causing a decrease in bond angle.

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Molecular Polarity

A molecule is polar if it has a net dipole moment. A dipole moment arises due to unequal sharing of electrons in a bond. Polar molecules have a positive and negative end.

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Bond Order (B.O.)

A measure of the strength of a bond. Calculated by subtracting the number of antibonding electrons from the number of bonding electrons, then dividing by 2.

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Bond Length (B.L.)

The distance between the nuclei of two atoms in a bond. Inversely proportional to bond order.

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Bond Strength (B.S.)

The energy required to break a bond. Directly proportional to bond order.

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HOMO & LUMO

HOMO (Highest Occupied Molecular Orbital) is the highest energy level occupied by electrons. LUMO (Lowest Unoccupied Molecular Orbital) is the lowest energy level that can accept electrons.

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Diatomic Species

Molecules composed of two atoms of the same element (homonuclear) or different elements (heteronuclear).

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What is e-e repulsion?

Electron-electron repulsion is the force of repulsion between electron pairs around a central atom in a molecule. This repulsion influences the shape of the molecule. Repulsion is strongest when electron pairs are at 90 degrees, and weakest at 180 or 120 degrees.

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What is Formal Charge?

Formal charge (F.C.) is a way to calculate the charge on an atom in a molecule. It helps to determine the most stable Lewis structure. It's calculated by subtracting the number of valence electrons assigned to the atom in the Lewis structure from its group number in the periodic table.

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What is a Dipole Moment?

A dipole moment (µ) is a measure of the separation of positive and negative charges within a molecule. It's a vector quantity, with both magnitude and direction.

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What makes a molecule nonpolar?

A molecule is nonpolar if its dipole moment is zero. This happens when the molecule has symmetrical distribution of electron density. This can happen with symmetrical shapes, like linear, tetrahedral, and octahedral.

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What makes a molecule polar?

A molecule is polar if the central atom is surrounded by different atoms, or has at least one lone pair, leading to an uneven distribution of electron density. This creates a partial positive and negative charge on opposite ends of the molecule.

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What is the relationship between VSEPR theory and molecular shape?

The VSEPR (Valence Shell Electron Pair Repulsion) theory helps predict the shape of a molecule based on the repulsion between electron pairs around the central atom. This allows us to understand how electron pairs arrange themselves to minimize repulsion, resulting in specific molecular shapes.

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What are the exceptions to the rule about central atoms?

There are a few exceptions to choosing the central atom based on its group number. Oxygen cannot be a central atom when bonded to halogens (Cl, Br, I), and instead, it should carry the negative charge in polyatomic ions. Halides can form a pi bond if they are central atoms.

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How is the number of pi bonds determined?

The number of pi bonds in a molecule is determined by the number of oxygen atoms and the charge of the molecule.

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Hydrogen's Bonding Limit

Hydrogen can only form one single (sigma) bond and cannot participate in pi bonding.

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Fluorine's Octet Rule

Fluorine always follows the octet rule, needing 8 electrons around it in a molecule.

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Central Atom Preference

In a molecule, the atom with the smaller group number is typically the central atom.

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Central Atom Row Preference

If two atoms in the same group are candidates for the central atom, the one in a lower row is preferred.

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AX2 Molecular Geometry

A molecule with two bonding groups and no lone pairs will be linear, with a 180 degree bond angle.

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AX3 Molecular Geometry

A molecule with three bonding groups and no lone pairs will be trigonal planar, with 120 degree bond angles.

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AX2E Molecular Geometry

A molecule with two bonding groups and one lone pair will have a bent or V-shaped geometry, with a bond angle slightly less than 120 degrees.

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AX4 Molecular Geometry

A molecule with four bonding groups and no lone pairs will be tetrahedral, with bond angles of 109.5 degrees.

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AX3E Molecular Geometry

A molecule with three bonding groups and one lone pair will be trigonal pyramidal, with a bond angle slightly less than 109.5 degrees.

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AX2E2 Molecular Geometry

A molecule with two bonding groups and two lone pairs will be bent or V-shaped, with a bond angle slightly less than 109.5 degrees.

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AX5 Molecular Geometry

A molecule with five bonding groups and no lone pairs will be trigonal bipyramidal, with bond angles of 90, 120, and 180 degrees.

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AX4E Molecular Geometry

A molecule with four bonding groups and one lone pair will be distorted tetrahedral or seesaw, with bond angles of 90, 120, and 180 degrees.

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AX3E2 Molecular Geometry

A molecule with three bonding groups and two lone pairs will be T-shaped, with bond angles of 90 and 180 degrees.

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AX2E3 Molecular Geometry

A molecule with two bonding groups and three lone pairs will be linear, with a bond angle of 180 degrees.

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AX6 Molecular Geometry

A molecule with six bonding groups and no lone pairs will be octahedral, with bond angles of 90 and 180 degrees.

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Study Notes

Chapter Nine: Chemical Bonding I - Basic Concepts

  • Chemical bonding is a fundamental process that underlies the formation of stable molecules essential for matter.

  • Atoms achieve noble gas electron configurations (adhering to the octet rule) to obtain stability, leading to molecule formation.

  • Only valence electrons, which are the outermost electrons, are considered when constructing Lewis structures, as they play a key role in bonding.

  • It is crucial that charges in Lewis structures correctly reflect the actual charge distribution in the molecule, ensuring accurate representation.

  • Chemical bonding is a fundamental process for forming stable molecules

  • Atoms achieve noble gas electron configurations (obey the octet rule) to form stable molecules

  • Valence electrons are the only electrons considered when building Lewis structures

  • Charges in Lewis structures should be minimized whenever possible

  • Second-row elements (C, N, O, F) adhere to the octet rule. Their valence orbitals (2s and 2p) can only accommodate eight valence electrons

  • Third-row elements (P, S, etc.) and heavier elements can sometimes exceed the octet rule by using d-orbitals

Chapter Ten: Chemical Bonding II - Molecular Geometry & Hybridization of Atomic Orbitals

  • Molecular structure determination relies on general rules
  • Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shapes based on electron-electron repulsion
  • Lone pairs require more space than bonding pairs, influencing bond angles.
  • Formal Charge (F.C.) is calculated to help determine the most stable Lewis structure
  • For a molecule to be polar, its dipole moment must be nonzero

Molecular Structure Determination - General Rules

  • The identification of molecular geometries and related properties in molecules relies on general rules, for example, the positions of electrons
  • The theory predicts molecular shapes based on electron-electron repulsion, which is fundamental in chemistry

Lewis Structures - Key Considerations

  • Only valence electrons are part of Lewis structures
  • Minimize charges to find the most stable structure
  • Second-row elements obey the octet rule
  • Third-row elements can exceed the octet rule if needed to form a stable structure
  • Hydrogen participates in bonds that use only two electrons

Bond Types

  • σ-bonds involve head-on overlap forming a strong bond.
  • Ï€-bonds are formed by side-to-side overlap resulting in a weaker bond.
  • Multiple bonds consist of sigma(σ) and pi (Ï€) bonds

Bond Order and Properties

  • Bond order relates to bond strength and length. A higher bond order means a stronger bond and shorter length
  • Bond order (B.O.) is calculated from the difference between bonding and antibonding electrons in Molecular Orbital (MO) diagrams.

Molecular Shapes

  • Different molecular geometries (linear, planar triangular, tetrahedral, etc.) can be predicted from the number of bonding pairs and lone pairs around the central atom
  • Molecular geometries are crucial to predict the structure and properties of molecules

Resonance Structures

  • Resonance forms are alternate Lewis structures for molecules with delocalized electrons, and exhibit the same geometry but different arrangements of electrons
  • The actual structure is a hybrid of all resonance structures.
  • Bond order in resonance structures refers to the average bond strength observed in the molecule

Molecular Orbital Theory

  • Molecular orbital (MO) theory describes bonding in diatomic molecules by combining atomic orbitals
  • Homo-nuclear diatomic species include molecules of the same element
  • Hetero-nuclear diatomic species include molecules of different elements
  • Bond order (B.O.) in MO theory reflects the number of bonding electrons minus the number of antibonding electrons, divided by 2
  • Bond properties, including strength, length, and magnetism, are related to the bond order

Summary of 2nd Row Diatomic Molecules

  • The MO summary for 2nd row elements (B2, C2, N2, O2, F2) illustrates bond order, magnetism, and bond energy
  • The higher the bond order, the stronger the bond

Additional Specific Information on Species

  • Various specific examples (NO2+, NO3-, NO2, SO42-, etc.) are studied to understand their structure and properties for each case
  • Applying the general rules and principles.

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CHM 101 Chapters 9,10 PDF

Description

Explore the fundamental concepts of chemical bonding in Chapters Nine and Ten. Learn about the formation of stable molecules, the octet rule, and the molecular geometry influenced by VSEPR theory. This quiz covers key principles essential for understanding chemical structures and bond hybridization.

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