Unit 4.2 Resonance, Shapes, and Giant Structures

Resonance Structures

Structures that represent different possible arrangements of electrons in a molecule, ion, or solid metal, where the electrons are delocalized and not permanently associated with one atom or covalent bond.

Nitrate (V) Ion

A molecule with 1 double bond and 2 single bonds, which has 3 possible resonance structures where the double bond moves around and is with each of the three oxygens.

Resonance Hybrid

The actual structure of a molecule that is a combination or intermediate between multiple resonance structures, where the electron density is spread evenly between atoms and the bond lengths are between a single and a double bond.

Valence Shell Electron Pair Repulsion (VSEPR) Theory

A theory that predicts molecular shape and bond angles based on the concept that electron pairs, both bonding and lone pairs, arrange themselves as far apart in space as possible.

Steric Number (SN)

The sum of the number of atoms and lone pairs around the central atom in a molecule, which determines the molecular shape according to VSEPR theory.

Linear

A molecular geometry where the central atom is bonded to two other atoms, resulting in a bond angle of 180°.

Trigonal Planar

A molecular shape where the central atom is bonded to three other atoms, resulting in a bond angle of 120°.

Bent Linear

A molecular geometry where the central atom is bonded to two other atoms and has one lone pair, resulting in a bond angle slightly less than 120°.

Tetrahedral

A molecular geometry where the central atom is bonded to four other atoms, resulting in a bond angle of 109.5°.

Trigonal Pyramidal

A molecular shape where the central atom is bonded to three other atoms and has one lone pair, resulting in a bond angle slightly less than 109.5°.

Bent

A molecular geometry where the central atom is bonded to two other atoms and has two lone pairs, resulting in a bond angle slightly less than 109.5°.

Molecular Polarity

The overall polarity of a molecule, determined by the arrangement of polar bonds and whether their dipole moments cancel each other out.

Giant Covalent Structures

Covalent lattices where the bonds between atoms continue forever, forming a large lattice with no separate molecules.

Allotrope

Different atomic or molecular arrangements of the same element in the same physical state.

Diamond

A giant lattice of carbon atoms, where each carbon is covalently bonded to four others in a tetrahedral geometry, resulting in a very hard substance.

Graphite

A layered structure of carbon atoms, where each carbon is bonded to three others in a hexagonal pattern, and the spare electron is delocalized between the layers.

Buckminsterfullerene

A molecule containing 60 carbon atoms, where each atom is bonded to three others by single covalent bonds and the fourth electron is delocalized, allowing for semi-conducting properties.

Graphene

A single layer of carbon atoms bonded in a repeating hexagonal pattern, considered a 2D material due to its thinness and has unique properties such as strength, flexibility, and transparency.