Chemistry Chapter 8: Lewis Dot Structures

Questions and Answers

What are Lewis Dot Structures?

Lewis Dot Structures show the number of valence (s and p) electrons.

What is the Octet Rule in Lewis Structures?

Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons.

Which element always breaks the octet rule?

Hydrogen

List the steps for drawing Lewis Dot Structures: 1) Sum the # of valence electrons. 2) Find the __________.

central atom Signup and view all the answers

What must you take into account when summing valence electrons for an ion?

Overall charge Signup and view all the answers

What is the central atom of a Lewis Dot Structure for covalent bonds usually?

Usually the first atom in the compound, or the atom that can form the most bonds or is least electronegative. Signup and view all the answers

What is a Resonance Structure?

When multiple Lewis Dot Structures for a molecule can occur. Signup and view all the answers

What is the formal charge formula?

Formal charge = valence electrons - (bonds + dots) Signup and view all the answers

How to determine the dominant Lewis Structure?

Atoms have formal charges closest to zero and the negative formal charge is on the most electronegative atom. Signup and view all the answers

What atoms always form octets, and how many bonds do they typically form? (F, O, N, C) Bonds: _, _, _, _

1, 2, 3, 4 Signup and view all the answers

Which elements can form ions/molecules with less than an octet?

Typically B and Be. Signup and view all the answers

If filling the octet of a central atom results in a negative charge on the central atom, should you complete the octet?

False Signup and view all the answers

Which elements can form ions/molecules with an expanded octet?

Period 3 and below elements Signup and view all the answers

What atom often forms an expanded octet?

Phosphorous Signup and view all the answers

What is the molecular formula of benzene?

C6H6 Signup and view all the answers

Study Notes

Lewis Dot Structures

Represent the number of valence electrons (s and p) in atoms.
Essential for understanding molecular bonding and electron arrangements.

Octet Rule

Atoms aim to achieve eight valence electrons for stability by gaining, losing, or sharing electrons.

Hydrogen Exception

Hydrogen violates the octet rule, requiring only 2 valence electrons to achieve stability.

Steps for Drawing Lewis Dot Structures

Sum total valence electrons from all atoms.
Identify the central atom, typically the least electronegative or one that can form the most bonds.
Connect surrounding atoms using single bonds, adjusting valence count accordingly.
Complete the octets of outer atoms and adjust valence count.
Place any remaining electrons on the central atom.
If the central atom lacks an octet, consider forming double or triple bonds.
Determine the dominant structure based on formal charges if necessary.

Valence Electrons in Ions

For ions, adjust total valence electrons based on charge: add for anions, subtract for cations.

Lone Pair vs Bonding Pair

Lone pairs are non-bonding electrons localized on an atom, while bonding pairs are shared between atoms in a bond.

Lewis Dot Structures for Ions

Indicate charge outside brackets for monoatomic and polyatomic ions.

Identifying the Central Atom

Generally the first listed atom, which can form the most bonds and is the least electronegative.
Hydrogen is never the central atom, while carbon is always included; common central atoms include C, N, P, S.

Resonance Structure

Drawn for molecules with multiple valid Lewis structures, representing delocalized electron sharing.

Formal Charge

Indicates the hypothetical charge on an atom if bonding electrons are shared equally.
Calculated with the formula: formal charge = valence electrons - (bonds + dots).

Determining Dominant Lewis Structure

Focus on structures with formal charges closest to zero.
Prefer negative formal charges on the most electronegative atoms.

Elements Forming Octets

Fluorine (F), Oxygen (O), Nitrogen (N), Carbon (C) typically form octets with bonding patterns of 1, 2, 3, and 4 respectively.

Elements Forming Less than Octets

Beryllium (Be) and Boron (B) often form stable configurations with fewer than eight electrons.

Completing Central Atom Octets

Avoid completing the octet of a central atom if it leads to a negative charge on the central atom and a positive charge on an electronegative outer atom.

Expanded Octet Formation

Elements in period 3 and below can exceed eight valence electrons by utilizing d orbitals for additional bonding.

Oxidation Number and Expanded Octet

A discrepancy between oxidation number and regular charge suggests a requirement for an expanded octet.

Common Element for Expanded Octets

Phosphorous frequently participates in forming expanded octets.

Benzene (C6H6)

Exhibits resonance structures due to delocalized electrons within the cyclic arrangement.

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Description

This quiz covers the essential rules and concepts related to Lewis Dot Structures, including the octet rule and specific exceptions. Test your knowledge on how to depict valence electrons and the structural representation of molecules. Perfect for chemistry students looking to reinforce their understanding of bonding and electron configurations.