CHEM 12 Lewis Structure Flashcards

Questions and Answers

Based on molecular geometry, which of the following molecules could have net dipole moments if all bonds present were polar? (Select all that apply)

PCl3 (P is the central atom) (correct)

CS2

ClNO (N is the central atom) (correct)

SeS2 (correct)

What is the bond structure in the resonance hybrid for NO−2?

One covalent bond and one partial bond

In what ratio will sodium ions and sulfide ions combine to give sodium sulfide?

2:1

Identify the Lewis structure of sodium chloride.

Na+[ :..Cl..: ]− Signup and view all the answers

How many bonds and lone pairs does the carbon monoxide molecule have?

3 bonds and 2 lone pairs Signup and view all the answers

What is the Lewis symbol for K+?

K^+ Signup and view all the answers

What does the equation `Ca` --> Ca^2+ + 2e^- represent?

Cations are formed by losing valence electrons. Signup and view all the answers

The tendency for elements to form compounds with zero or eight valence electrons is called the?

Octet rule Signup and view all the answers

Identify the correct Lewis structure of potassium fluoride.

K+ { :..F..: }− Signup and view all the answers

A Lewis symbol that has a non-noble gas element with no dots represents a?

Cation Signup and view all the answers

What is an exception to the octet rule?

Hydrogen is almost never a central atom. Signup and view all the answers

How many valence electrons does the cyanide ion (CN−) have?

10 electrons and 3 bonds Signup and view all the answers

Which of the following is the correct Lewis structure for carbon dioxide CO2?

:O..=C=..O: Signup and view all the answers

Identify the tendency of main group atoms to form enough bonds to obtain eight valence electrons.

Octet rule Signup and view all the answers

A group 14 element has four electrons in its outermost shell; how many more electrons does it need to reach an octet?

4 bonds Signup and view all the answers

Group 15 elements form?

Three covalent bonds. Signup and view all the answers

The other halogen molecules form?

A single bond and 3 lone pairs. Signup and view all the answers

Lead (Pb) is a group 14 element which has 4 valence electrons. How many bonds does this element usually form?

4 Signup and view all the answers

How many electrons does hydrogen need to gain to fill its outermost shell?

1 Signup and view all the answers

What are odd-electron molecules?

They have an odd number of valence electrons. Signup and view all the answers

What are electron-deficient molecules?

They have a central atom that has fewer electrons than needed for a noble gas configuration. Signup and view all the answers

What are hypervalent molecules?

They have a central atom surrounded by more electrons than needed for a noble gas configuration. Signup and view all the answers

What do we call molecules that contain an odd number of electrons?

Free radicals. Signup and view all the answers

List the steps for dealing with odd-electron molecules.

<ol> <li>Determine the total number of valence electrons. 2. Draw a skeleton structure. 3. Distribute remaining electrons as lone pairs. 4. Place remaining electrons on the central atom. 5. Rearrange electrons to form bonds.</li> </ol> Signup and view all the answers

Describe electron-deficient molecules.

Generally, these are molecules with central atoms from groups 2 and 13. Signup and view all the answers

A molecule contains a central atom from Group 13 that shows no characteristics of a free radical. It is most likely?

An electron-deficient molecule. Signup and view all the answers

What will a central atom from Group 13 most likely display?

An electron-deficient nature. Signup and view all the answers

Electron-deficient molecules react with?

Molecules with lone pairs. Signup and view all the answers

Which molecule will have a double bond?

H2CO Signup and view all the answers

When drawing the Lewis structure for a molecule, what should be done if the central atom does not have a complete octet?

Rearrange lone pairs of electrons from the outer atom(s) to form double or triple bonds to the central atom. Signup and view all the answers

What must be done once all of the valence electrons have been placed on a Lewis structure?

Rearrange electrons to satisfy the octet rule Signup and view all the answers

How can we predict the number of bonds an atom can form?

By knowing the number of electrons needed to form an octet. Signup and view all the answers

Which of the following elements can NOT form hypervalent molecules? (Select all that apply)

N Signup and view all the answers

Which of the following is very reactive and can readily combine with molecules containing atoms with lone pairs?

Electron-deficient molecules Signup and view all the answers

What is the actual electronic structure of a molecule, reflecting an average of resonance forms?

Resonance hybrid of the individual resonance forms. Signup and view all the answers

Is a resonance hybrid the actual structure of a given molecule?

Yes, based on experimental evidence. Signup and view all the answers

Does a resonance hybrid fluctuate between resonance forms?

No. Signup and view all the answers

Which of the following is true of a resonance hybrid? (Select all that apply)

It has some characteristics of its resonance forms. Signup and view all the answers

What is the structure that represents the averaging of all resonance forms called?

Resonance hybrid. Signup and view all the answers

Which molecule will NOT exhibit resonance?

CO2 Signup and view all the answers

How can resonance structures be described?

They represent electronic structures equal to that of a combination of the resonance structures. Signup and view all the answers

What is crucial about resonance structures concerning overall electronic structure?

They do not fluctuate over time. Signup and view all the answers

How does electron-pair geometry differ from molecular structure?

Electron-pair geometry shows the placement of all valence electrons; molecular structure shows only the placement of atoms. Signup and view all the answers

What does VSEPR theory use to illustrate molecular shapes?

The wedge and dash notation. Signup and view all the answers

Order the electron-pair repulsions from greatest to least.

Lone pair−lone pair > lone pair−bonding pair > bonding pair−bonding pair Signup and view all the answers

What is the size ordering of bonds based on their electron occupation?

Lone pair > triple bond > double bond > single bond Signup and view all the answers

What is the bond angle for a molecule with two electron domains?

180 degrees Signup and view all the answers

Which pair of molecules has the same electron-pair geometry?

SF6 and XeF4 Signup and view all the answers

What determines how strongly an atom attracts the electrons in its bonds?

Its electronegativity. Signup and view all the answers

What is the bond type in the molecule MgO?

Ionic bond. Signup and view all the answers

What is the formula for bond dipole moment?

μ=Qr Signup and view all the answers

Which of the following has the largest dipole moment?

NCl3 Signup and view all the answers

Which molecule has bonds with the greatest bond-polarity?

H2O Signup and view all the answers

Which of the following is the least polar?

ICl Signup and view all the answers

What does the net dipole moment of PF5 look like?

The dipole moment is 0. Signup and view all the answers

Which equation accurately represents bond dipole moment?

μ depends on the magnitude of the partial charges and the distance between the charges. Signup and view all the answers

Study Notes

Ionic Compounds and Lewis Structures

Sodium ions (Na⁺) and sulfide ions (S²⁻) combine in a 2:1 ratio to form sodium sulfide, achieving electrical neutrality.
The Lewis structure for sodium chloride (NaCl) is represented as Na⁺[:Cl⋅⋅⋅⋅:]⁻, illustrating the transfer of Na's one valence electron to Cl.
Potassium fluoride (KF) features a Lewis structure of K⁺ { :..F..: }⁻, showing ionic bonding between the elements.

Valence Electrons and Bonding

Carbon monoxide (CO) contains 3 bonds and 2 lone pairs, indicating its triple bond structure.
The cyanide ion (CN⁻) contains a total of 10 electrons in its Lewis structure and has 3 bonds.
Cations, such as K⁺, are represented by Lewis symbols with no valence electron dots.

Octet Rule and Bonding Theories

The octet rule predicts that atoms bond to achieve a stable configuration of zero or eight valence electrons.
Group 14 elements typically form 4 bonds, while group 15 elements form 3 covalent bonds.
Hydrogen requires 1 additional electron to fill its outermost shell.

Molecule Types and Exceptions

Odd-electron molecules possess an unpaired electron, while electron-deficient molecules have fewer electrons than needed for a stable configuration.
Hypervalent molecules possess a central atom surrounded by more electrons than required for a noble gas configuration.

Resonance and Molecular Structure

Resonance structures represent different electron configurations of a molecule, contributing to an average structure known as the resonance hybrid.
CO₂ exhibits no resonance as it has strictly localized electrons.
A resonance hybrid reflects the average of resonance forms, showing properties of all forms and not fluctuating between them.

VSEPR Theory and Molecular Geometry

VSEPR (Valence Shell Electron Pair Repulsion) theory focuses on predicting molecular shapes based on repulsions between electron domains.
Electron-pair geometry differs from molecular structure: geometry considers all electron regions, while structure focuses on the arrangement of atoms.
Lone pairs exert greater repulsive force than bonding pairs, influencing the spatial arrangement of atoms significantly.

Electronegativity and Bonding

Electronegativity, the attraction of an atom for electrons in a bond, dictates the polarity of bonds. The greater the difference in electronegativity, the more polar the bond.
Ionic bonds, like that found in MgO, involve a complete transfer of electrons from one atom to another.

Dipole Moments and Molecular Polarity

The bond dipole moment is calculated using the formula μ = Qr, where Q represents the magnitude of partial charges and r is the distance between charges.
Molecules like NCl₃ possess net dipole moments due to polar bonds, while symmetrical molecules like CS₂ do not have resulting polar characteristics.

Summary of Key Molecular Characteristics

Hybridization is determined by the number of electron domains around a central atom.
In molecular geometry, bond angles may vary; for example, linear geometries have 180° bond angles.
Some molecules, like PCl₃ and ClNO, can exhibit net dipole moments based on their geometrical structure.

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Description

This quiz focuses on the Lewis structures of key ionic compounds, specifically sodium sulfide and sodium chloride. Test your understanding of ionic ratios and the representation of ionic compounds through Lewis dot structures.