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Unit 5: The Structure of Molecules—Lewis Structures and Molecular Geometries

Glossary

Pi (π ) bond
A covalent sharing of electrons formed by the side-to-side overlap of two p orbitals; found in double and triple bonds.
Sigma (σ ) bonds
A covalent sharing of electrons that is formed by head-to-head overlap between two atomic orbitals and is cylindrically symmetrical about the axis between the nuclei.
Aqueous solution
A solution where the solvent (primary component) is water.
Bond
An association between two atoms in which they remain close together in space due to some type of electron-based interaction.
Central atom
The atom for which we are determining the geometry when applying VSEPR theory.
Coulombic forces
Attractive or repulsive forces exerted by particles that bear an electric charge on other particles that also bear an electric charge. Like charges repel each other, and opposite charges attract each other.
Covalent bond
A bond formed by the sharing of electrons between two atoms, as distinct from an ionic bond in which atoms are held together because they have opposite charges.
Dipole forces
The intermolecular forces of attraction between molecules that are polar.
Double bond
A bond between two atoms when two pairs of electrons are shared.
Electron density
In an electron cloud, the chance of finding that electron per volume in a given region of space.
Expanded octet
The situation in which a third row or higher element violates the octet rule, by having more than eight valence electrons and usually forming more than four bonds.
Formal charge
An assignment of charge to each of the atoms in a molecule, based on the difference between their valence electrons and the electrons they control.
Hydrogen bonding
A type of intermolecular attraction in which a hydrogen is shared between two very electronegative atoms atoms. This commonly happens when a hydrogen is attached to a nitrogen or an oxygen atom, and the hydrogen reaches out to a nearby lone pair to make a weak bonding interaction.
Hydrophilic
Description of a molecule that dissolves easily in an aqueous or other polar solvent.
Hydrophobic
Description of a molecule that dissolves readily in a nonpolar solvent.
Intermolecular forces
Forces that exist between different molecules.
Ionic bond
A bond in which two atoms are held together by the fact that they possess opposite charges, as distinct from a covalent bond in which atoms are held together by the sharing of electrons.
Lewis dot structures
A way of representing molecular structures in which atoms and their electrons are represented as two-electrons bonds and lone pairs of electrons. Formal charges are assigned to each atom.
London dispersion forces
A type of intermolecular force that arises from brief, temporary dipoles in the electron cloud surrounding a molecule.
Lone pair
A pair of valence electrons on an atom not involved in a bond.
Molecular orbital
A region where atomic orbitals from different atoms overlap, creating a new orbital where electrons may be shared in a covalent bond.
Octet rule
The principle that covalent bonds form such that the shared electrons complete the valence shell of each atom. For the common atoms other than hydrogen, this means eight valence electrons.
Polar covalent bond
A covalent bond between two atoms of different electronegativities in which the electrons are shared unequally. The bond will be polarized toward the more electronegative atom.
Pure covalent bond
A covalent bond between two atoms of the same electronegativity, which equally share the electrons in the bond.
Single bond
A covalent bond between two atoms where just two electrons are being shared.
Substituents
The lone pairs and atoms of a molecule attached to the central atom when applying VSEPR theory.
Triple bond
A covalent bond between two atoms when they share three pairs of electrons.
VSEPR Theory
A theory that describes the shapes of molecules based on the mutual repulsion of the electron clouds surrounding the nucleus.
van der Waals force
A collective term for intermolecular forces, including London dispersion forces and dipole forces.

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