Chemistry Chapter 3
Terms in this set (61)
an atom tends to bond with other atoms so that it has eight electrons in its outermost shell, thereby forming a stable electron configuration similar to that of the noble gases
What are the three groups of exceptions to the octet rule?
1. incomplete octet
2. expanded octet
3. odd numbers of electrons
describe the "incomplete octet" exception to the octet rule
which elements fall under this rule?
several elements are stable with fewer than eight electrons in their valence shell
describe the "expanded octet" exception to the octet rule
any element in period 3 or greater can hold more than eight electrons
describe the "odd numbers of electrons" exception to the octet rule
any molecule with an odd number of valence electrons cannot distribute those electrons to give eight to each atom
NO (11 valence electrons)
which elements do abide by the octet rule?
what are the two types of chemical bonds?
ionic and covalent
what two types of molecules do they form between? what actually holds them together?
when one or more electrons from an atom with a low ionization energy, typically
a metal (NOT TRANSITION METAL)
, are transferred to an atom with a high electron affinity, typically
between opposite charges is what holds the ions together
creates lattice structures
what two types of molecules do they form between? how does this account for polarity?
an electron pair is shared between
, that have relatively similar values of electronegativity
(generally differ less than 1.7)
polarity is determined by the degree to which the pair of electrons is shared equally or unequally between two atoms
coordinate covalent bond
what two types of molecules do they form between? what type of reaction is an example? (
both of the shared electrons are contributed by only one of the two atoms
in a covalent bond (
this means any complex ion formed with a transition metal ion and nonmetal
generally, this means that a lone pair of one atom attacked another atom with an unhybridized p-orbital to form a bond
Lewis acid-base reaction
what periodic trend determines whether a covalent bond is polar or nonpolar?
atom in an ionic bond that loses the electrons
atom in an ionic bond that gains electrons
what two types of elements are ionic bonds normally formed between?
NOT TRANSITION METAL
) and nonmetal
describe characteristics of ionic compounds
MP and BP?
what are they in their solid states?
high MP and BP
dissolve readily in water and other polar substances
in solid state, form crystalline lattice
what forces are maximized? what forces are minimized?
what ionic compounds form in the solid state
repeating positive and negative ions
attractive forces are maximized
and repulsive forces are minimized
describe several properties of covalent compounds
MP and BP?
low MP and BP
poor conductors of electricity
what is the bond order of a single, double and triple bond?
number of shared electrons pairs
between two atoms
does it increase or decrease with increasing number of bonds?
the average distance between the two nuclei of atoms in a bond
increasing number of bonds--> decreasing bond length
do single, double or triple bonds have more bond energy?
the energy required to break a bond by separating its components into their isolated, gaseous atomic states
increasing number of bonds--> increasing energy
at what difference in electronegativity is a compound considered polar?
when two atoms have a relative difference in electronegativities (
the atoms with the higher electronegativity gets the larger share of the electron density (is more negative)
nonpolar covalent bond
at what electronegativity difference is a bond considered nonpolar?
bonds between what elements are perfectly nonpolar?
when atoms that have identical or nearly identical electronegativities share electron pairs and do so with equal distribution of electrons
any bond with an electronegativity difference of
less than 0.5 is nonpolar
only diatomic elements are perfectly nonpolar
seven diatomic molecules
(form a 7 on the periodic table)
polar covalent bond
how much do they have to differ in electronegativities by?
when atoms differ moderately in their electronegativities
(0.5 to 1.7)
and share electrons unevenly
where is the partial negative and partial positive in a polar bond?
partial negative on electron with more electron density (more electronegative)
partial positive on electron with less electron density (less electronegative)
what is the equation?
what units is it measured in?
a vector quantity of a polar molecule
p= dipole moment
q= magnitude of charge
d= displacement vector
electrons involved in a covalent bond that are in the valence shell
what is another name for them?
electrons in the valence shell that are not involved in covalent bonds
what is the purpose of a Lewis structure?
to keep track of the bonded and nonbonded electron pairs
Lewis dot structure
dots represent valence electrons
Describe the rules for assigning a Lewis structure to a molecule
1. Draw the backbone (H's and halogens occupy terminal positions)
2. Count all the valence electrons of the atoms. Add them up to determine the total number of valence electrons.
3. Draw single bonds between the central atom and the atoms surrounding it (each bond= 2 electrons)
4. Complete the octet for atoms that follow the octet rule by drawing in dots
5. Place any electrons left on the central atom
what is the equation for it?
the difference between the number of electrons assigned to an atom in a Lewis structure and the number of electrons normally found in that atom's valence shell
formal charge= V- N nonbonding - 1/2Nbonding
V= normal number of electrons in the atom's valence shell
Nnonbonding= number of nonbonding electrons
Nbonding= the number of bonding electrons
compare formal charge and oxidation number
the effect of electronegativity difference, whereas oxidation numbers
the effect of electronegativity differences
a Lewis structure that demonstrates the same arrangement of atoms but that differ in the specific placement of the electrons
the actual structure of a compound that considers contribution of all resonance structures
describe the three guidelines in using formal charge to assess the stability of resonance structures
1. a Lewis structure with small or no formal charges is preferred over a Lewis structure with large formal charges
2. a Lewis structure with
less separation between opposite charges
is preferred over a Lewis structure with a large separation of opposite charges
3. a Lewis structure in which
negative formal charges are placed on more electronegative atoms
is more stable than one in which the negative formal charges are placed on less electronegative atoms
what is the main premise behind the VSEPR theory
the three dimensional arrangement of atoms surrounding a central atom is
determined by the repulsions between bonding and nonbonding electron pairs
in the valence shell of the central atom
What are the three steps in determining the geometrical structure of a molecule using VSEPR theory?
1. Draw the Lewis structure
2. Count the total number of bonding and nonbonding electron pairs in the valence shell of the certain atom
3. Arrange the electron pairs around the central atom so that they are as far apart as possible
what are the five most common electronic configurations of molecules according to the VSEPR theory
(when 2 bonds attached)
(when three bonds attached)
(when four bonds attached)
(when five bonds attached)
(when six bonds attached)
describes the spatial arrangement of all pair of electrons around the central atom,
including both the bonding and lone pairs
describes the spatial arrangement of
only the bonding pairs of electrons
the number of
atoms that surround and are bonded to a central atom
(doesn't have to be a coordinate covalent bond to have a coordination number)
a relevant factor when determining molecular geometry
distinguish between molecular and electronic geometry
electronic geometry= the position of
all electrons in a molecule, whether bonding or nonbonding
(bent, trigonal pyramidal etc.)
molecular geometry= the position of
only the bonding pairs of electrons in a molecule
(linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral)
how is the ideal bond angle in electronic geometry different from molecular geometry
since you are also considering the
nonbonding pairs, they exert more repulsion than bonding pairs
does a polar bond within a molecule always mean that the entire molecule is polar?
no, there might be another opposing polar bond that cancels the other one out, resulting in an overall nonpolar molecule
however, if there is only one polar bond, or multiple that do not cancel out, then the overall molecule will have a net dipole moment
can sigma bonds have free rotation? pi bonds?
sigma yes because the head-to-head overlap allow for free rotation
pi no because the two parallel electron clouds do not allow for free rotation
what are the three intramolecular forces? rank them in order of weakest to strongest
how do all of them compare to a covalent bond?
London forces (van der waals) < dipole-dipole interactions < H-bonds<<<<<<<<<covalent bond
London dispersion forces
why are they the weakest?
when are they significant?
which molecules display them the most?
attractive or repulsive interactions between molecules due to short-lived or rapidly shifting dipoles
dipoles are short-lives and rapidly shifting
only in molecules that have
how are London dispersion forces and dipole-dipole forces different
, London dispersion are
what phases are they present during?
what physical property in molecules do these account for?
polar molecules tend to orient themselves in such a way that the oppositely charged ends of the respective molecular dipoles are closest to each other and
form an electrostatic force
solid and liquid phases
, not the gas phase
higher melting and boiling points
in polar species
what type of other IMF can H-bonds be classified under?
unusually strong dipole-dipole
what elements can hydrogens that participate in hydrogen bonding be attached to?
what type of interaction can it also be categorized as?
unusually strong form of a dipole-dipole interaction
intra- or inter- molecular
not actually bonds- no sharing or transfer of electrons between two atoms, but rather electronegative atoms disproportionately carry shared electron pairs when bonded to hydrogen
exist between H-s bonded to O, N or F
substances that display hydrogen bonding have unusually high _________
if you are comparing the strength of a dipole moment in two compounds and one is linear and the other is bent, which will have the larger dipole moment?
the linear atom
when a compound like H2O or NH3 gains a proton is it forming a nonpolar covalent bond or a coordinate covalent bond?
coordinate covalent bond
linear molecules have what hybridization and bond angle?
trigonal planar molecules have what hybridization and bond angle?
tetrahedral, trigonal pyramidal and bent molecules have what hybridization and bond angle?
trigonal-bipyramidal, see-saw, t-shaped all have what hybridization and bond angle?
sp3d, 90 and 120
octahedral, square pyramidal and square planar molecules have what hybridization and bond angle?
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