AP Chem Ch. 9 Bonding & Molecular Structure: Fundamental Concepts Flashcards

Terms Definitions
valence electrons
electrons in outermost shell of atom that determine chemical properties of element
core electrons
electrons not involved in chemical behavior
Lewis electron dot symbols
pictures in which the element's symbol is chosen to represent the atomic nucleus together with the core electrons; up to 4 electrons, represented by dots, are placed around the symbol one at a time; then, if any electrons remain, they are paired with the ones already there
eight electrons
chemical bond
the net attractive force that occurs between atoms when a chemical reaction occurs and their valence electrons are reorganized
ionic bond
forms when one or more valence electrons is transferred from one atom to another, creating positive & negative ions; in the Lewis electron dot structure representations: the electron pair in sodium chloride has become pair of the valence shell of chlorine; high melting points
covalent bonding
involves sharing of valence electrons between atoms; i.e.: 2 chlorine atoms share a pair of electrons; in a chlorine molecule, the electron pair is found midway between the 2 atoms & is shared equally by them
lattice energy
E (subscript lattice); energy of formation of 1 mole of solid crystalline ionic compounds when ions in the gas phase combine; for an ionic compound, results from attraction between cations & anions in a crystal; not possible to measure directly, but it is possible to calculate; values can be determined from measurable thermodynamic parameters
Lewis structure
structure that uses line or shared electrons to represent covalent bond
bond pair
the pair of electrons that bond
lone pairs/non-bonding electrons
the six pairs of electrons that reside on 1 atom; not involved in bonding
double bond
in carbon dioxide, for example, the carbon atom shares 2 pairs of electrons with each oxygen & so it is linked to each O atom by a ________
triple bond
for example, in dinitrogen, the 2 nitrogen atoms share 3 pairs of electrons, so they are linked by a ________
octet rule
the tendency of a covalent species to have a structure in which 8 electrons surround each atom; directs you to seek a Lewis structure for covalent compounds in which each atom has 8 electrons in its valence shell; can't be applied when there are more than 4 bonds to an element or when there is an odd number of electrons
molecules & ions having the same # of valence electrons & the same Lewis structures
theory of resonance
proprosed by Linus Pauling; resonance structures are a way to represent bonding in a molecule or ion when a single Lewis sructure fails to describe accureately the actual electronic structure
contributing structures/resonance structures
alternative structures shown for ozone; have identical patterns of bonding & equal energy
resonance hybrid
composite of the equivalent contributing structures
coordinate covalent bond
describes bond in which the bonding pair of electrons originates on one of the bonded atoms; in Lewis structures, a ______ is designated by an arrow that points away from the atom donating the electron pair
free radicals
atoms & molecules with an unpaired electron
order of a bond
number of bonding electron pairs shared by 2 atoms in a molecule
bond length
distance between nuclei of 2 bonded atoms; largely determined by sizes of atoms
bond dissociation energy
symbolized by D; enthalpy change for breaking bond in molecule w/ reactants & products in gas phase under standard conditions; has positive value; process of breaking bonds in molecule always endothermic
partial charges
result of uneven valence electron distribution among covalent bonds - some atoms may have a slight negative charge & others a slight positive charge b/c (1) when forming bonds, some atoms contribute more electrons than they get back; (2) the elctron pair or pairs in a given bond may be drawn more strongly toward 1 atom than another
charge distribution
the way partial charges are distributed
formal charge
(for an atom in a molecule or ion) the charge calculates for that atom based on the Lewis structure of the molecule or ion using the equation: formal charge of an atom in a molecule or ion = group # of the atom - [# of line pair electrons + 1/2 (# of bonding electrons)], where the group # represents the # of valence electrons in a free atom, the # of electrons assigned by the Lewis structure to an atom in a molecule or ion is calculated by the term w/in the square brackets; an atom will be + if it "contributes" more electrons to bonding than "gets back" when in a molecule; assume in this equation that lone pairs are assumed to belong to the element on which they reside in the Lewis structure; bond pairs are assumed to be shared equally between the bonded atoms; the sum of the ______ on the atoms in a molecule or ion always equals its net charge
polar covalent bond
bond in which 2 atoms have residual or partial charges; occurs when 2 dissimilar atoms form a covalent bond & the electron pair is unequally shared
polar/bipolar bond
bond between 2 atoms has + end & - end; that is, it has negative & positive poles
polar covalent bond
polarity is indicated by symbols δ+ and δ- alongside the atom symbols, where δ (the Greek letter "delta") stands for partial charge
nonpolar covalent
describes bond in which there is no net displacement of the bond electron pair
parameter proposed by Linus Pauling in 1930s; allows us to decide if a bond is polar, which atom of the bond is negative & which is positive & if 1 bond is more polar than another; X; measure of the ability of an atom in a molecule to attract electrons to itself
electroneutrality principle
all electrons in a molecule are distributed in such a way that the charges on the atoms are as close to zero as possible; if there is a negative charge, it should be placed on the most electronegative atom; a positive charge should be on the least electronegative atom
valence shell electron-pair repulsion (VSEPR) model
devised by Ronald J. Gillespie (1924 - ) & Ronald S. Nyholm (1917 - 1971); reliable method for predicting shapes of covalent molecules & polyatomic ions; based on idea that bond & lone electron pairs in the valence shell of an element repel each other & seek to be as far apart as possible; not generally used to predict structures of molecules based on transition metal atoms
describes geometry for 2 bond pairs; involves central atom that does not have an octet of electrons
describes geometry for 3 bond pairs; involves central atom that does not have an octet of electrons
describes molecules in which the central atom obeys the octet rule w/ 4 bond pairs
describes molecule in which the central atoms have 5 bonding pairs & is expected when the central atom is an element in Period 3 or higher of the periodic table
describes molecule in which the central atoms have 6 bonding pairs & is expected when the central atom is an element in Period 3 or higher of the periodic table
electron-pair geometry
geometry taken up by all the valence electron pairs around a central atom
molecular geometry
involves arrangement in space of central atom & atoms directly attached to it
dipole movement
μ; product of magnitude of partial charges (δ+ and δ-) & distance by which separated; SI unit is coloumb-meter; traditional derived unit is debye (D; 1 D = 3.34 * 10⁻³⁰ C * m); determined experimentally
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