CHM 2045C Chapter 9 Key Terms

Bonding and Molecular Structure: Fundamental Concepts

*Module 4 Part I Vocabulary

Axial: in the trigonal bipyramidal electron-pair geometry, the two positions directly across from each other

Bent: the molecular geometry that results when two atoms and one lone pair are connected to a central atom in the trigonal planar electron-pair geometry and when two atoms and tow lone pairs are connected to a central atom with the tetrahedral electron-pair geometry

Bond angle: the angle formed between two atoms that are connected to the same central atom

Bond dissociation energy (D): the enthalpy change for breaking a bond in a molecule with the reactants and products in the gas phase

Bond length: the distance between the nuclei of two bonded atoms

Bond order: the number of bonding electron pairs shared by two atoms in a molecule or polyatomic

Bonding pair: a pair of electron that is shared between two atoms

Bonding: describes the forces that hold adjacent atoms together

Born-Haber cycle: an energy cycle in which the formation of one mole of a solid crystalline ionic compound from its elements is pictured as going through the following steps: conversion of the elements to gaseous monatomic atoms, the loss of electrons by the metal atoms, the gain of electrons by the nonmetal atoms, and finally the formation of a solid crystal lattice from the isolated ions in the gas phase; the overall some of this cycle will equal the enthalpy of formation of the solid crystalline ionic compound

*Chemical bond: an interaction between the valence electrons in two atoms that results in an attractive force between two atoms

*Coordinate covalent bond: a covalent bond in which both electrons in the bond were contributed by one atom

*Core electrons: all of the electrons in an atom except for the valence electrons

*Covalent bond: a force of attraction between two atoms that results from the sharing of electrons in the valence shells of two atoms

Dipole moment (μ): the product of the magnitude of the partial charges on a molecule and the distance by which they are separated. The dipole moment is a vector quantity having both a magnitude and a direction

*Double bond: a double bond exists when four electrons are shared by two atoms; two pairs of electrons are shared

*Electronegativity (_X): a measure of the ability of an atom in a molecule to attract electrons to itself

Electroneutrality principle: electrons in a molecule or Polyatomic ion will be distributed in such a way that the charges on all atoms are as close to zero as possible

Electron-pair geometry: the geometry taken up the valence electron pairs around a central atom

Equatorial: in the trigonal bipyramidal electron-pair geometry, the three positions in a plane midway between the two axial positions

Formal charge: the charge calculated for an atom by comparing the number of valence electrons in an atom in a molecule or polyatomic ion (in which lone pairs are assigned solely to the atom and bonding pairs are evenly split between the two atoms involved in the bond) to the number of valence electrons that a free atom of that element would have. It is calculated by the equation: Formal charge = group number - {Lone pair electrons + ½ bonding electrons}

Free radical: a chemical species containing an unpaired electron; these tend to be very reactive

*Ionic bond: the electrostatic attraction between two oppositely charged ions. Ion formation results from the transfer of electrons from one atom to another

*Isoelectronic: containing the same number and arrangement of valence electrons

Isostructural: having the same structure

Lattice energy: the energy for the formation of one mole of a solid crystalline ionic compound from its constituent ions in the gas phase

*Lewis electron dot symbol: in a Lewis dot symbol for an element, the chemical symbol is used to represent the nucleus and core electrons often atom; the valence electrons are represented by dots placed around the symbol

*Lewis structure: a representation of a covalently bonded species in which the chemical symbol is used to represent the nucleus and core electrons of each atom; a lone pair belonging solely to one atom is represented by two dots and a pair of electron that is shared between two atoms is represented by a line connecting the two atoms

Linear: the electron-pair geometry having two groups connected to a central atom, and the molecular geometry that results when both groups connected central atom in the linear electron-pair geometry are atoms and when two atoms and three lone pairs are connected to a central atom in the trigonal bipyramidal electron-pair geometry

*Lone pair: a pair of electrons that belongs solely to one atom in a covalent species; these are nonbonding electrons

Molecular geometry- the arrangement of the central atom and the atoms attached to it

*Nonbonding electrons: electrons that are not shared between atoms in a covalent species; they belong solely to one atom

Nonpolar covalent bond: a bond in which the bonding electrons are shared equally between the two bonded atoms

Octahedral: the electron-pair geometry when six groups are connected to a central atom and the molecular geometry when all six groups in an octahedral electron-pair geometry are atoms

Octet rule: the atoms of many elements lose, gain, or share electrons to obtain eight electrons in the highest energy level

*Octet: an electron configuration having completed s and p sublevels in the highest energy level. All of the noble gases (except helium) have this configuration

Polar covalent bond: a bond that involves sharing electrons but in which the two atoms do not share the electrons equally. One of the atoms will be partially positive, and one will be partially negative

Resonance hybrid: the actual structure of a molecule or ion that exhibits resonance; it is somewhere in between, a composite of, the resonance structures that can be drawn

Resonance structures: these are used to represent bonding in a molecule or ion when a single Lewis structure fails to describe accurately the actual electronic structure

Seesaw: the molecular geometry when four atoms and one lone pair are connected to a central atom with the trigonal bipyramidal electron-pair geometry

Square planar: the molecular geometry when four atoms and one lone pair are connected to a central atom with the trigonal bipyramidal electron-pair geometry

Square planar: the molecular geometry when four atoms and one lone pair are connected to a central atom with the octahedral electron-pair geometry

Square Pyramidal: the molecular geometry when five atoms and one lone pair are connected to a central atom with the octahedral electron-pair geometry

Structure: the way atoms are arranged in space

Tetrahedral: the electron-pair geometry having four groups connected to a central atom and the molecular geometry when all four groups in tetrahedral electron-pair geometry are atoms

Trigonal bipyramidal: the electron-pair geometry when five groups are connected to central atom and the molecular geometry when all five groups in a trigonal bipyramidal electron-pair geometry are atoms

Trigonal planar: the electron-pair geometry having three groups connected to a central atom, and the molecular geometry that results when all three groups connected to a central atom with the trigonal planar electron-pair geometry are atoms

Trigonal pyramidal: the molecular geometry when three atoms and one lone pair are connected to a central atom with the tetrahedral electron-pair geometry

*Triple bond: a triple bond exists when six electrons are shared by two atoms; three pairs of electrons are shared

T-shaped: the molecular geometry when three atoms and two lone pairs are connected to a central atom with the trigonal bipyramidal electron-pair geometry

*Valence electrons: for a main group element, the valence electrons are the s and p electrons of the highest energy level. For transition metals, they are the electrons in the highest energy level s orbital as well as the electrons in the partially filled d subshell of the next highest energy level

Valence shell electron-pair repulsion (VSEPR) model: bonding and lone pair electron pairs in the valence shell of an element repel each other and seek to be as far apart as possible