Chapter 9: Chemical Bonds Flashcards
the … electrons form bonds
valence
a lewis-dot symbol for an atom consists of the
symbol for the element surrounded by dots, one for each valence electron
electrons are usually removed from groups 1 and 2 because they have
low ionization energies
electrons are easily added to nonmetals because their
electron affinities are generally favorable
ionic bonding is the bonding that results from
electrostatic attraction between positively and negatively charged ions
when an ionic coompound forms, the number of electrons lost in forming the cations must
equal the number gained to form the anions
born-haber cycle: a process in which the formation of an ionic compond is shown as the
sum of five simpler reactions
lattice energy is the energy required to separate
one mole of an ionic crystalline solid into the isolated gaseous ions
lattice enrgy is always
positive
E=
kQ1Q2/ r
k is a
constant
Q1 and Q2 are the
charges on the two particles
r is the
distance of separation in the compound
equation for E known as
coulomb’s law
lattice energies are greatest for compounds made from
highly charged small ions
maximize …, minimize … to get the largest E
Q; r
ionic solids are stable because of
high lattice energies
ionic compounds are typically … with …
brittle solids; high melting points
covalent compounds are typically … or … at …
liquids; gases; room temperature
when covalent compounds are solids, they are
low melting
a covalent bond is a bond that results from
atoms sharing electrons
the bond length is the … between the … in a molecule
minimum energy distance; nuclei of two bonded atoms
bond length is determined by a … observed as the two atoms move ..
potential energy minimum; closer together
a covalent bond forms because two atoms sharing electrons are
lower in energy than the two isolated atoms
bonding pairs of electrons are
shared between two atoms
lone, or nonbonding, pairs of electrons are entirely
on one atom and are not shared
lewis structures show how valence electrons are
arranged among atoms in a molecule
lewis structures reflect the central idea that stability of a compound relates to
noble gas electron configuration
lewis structures show the .. and …, not the …
numbers; types of bonds; geometry of the molecule
The octet rule states that each atom in a molecule shares electrons until it is
Surrounded by eight electrons
In most Lewis structures oxygen makes … bonds and has … lone electrons; nitrogen makes … bonds and has … lone pair; carbon makes … bonds
Two; two; three; one; four
Single bond;
Shares one electron pair
Double bond:
Shares two electron pairs
Triple bond:
Shares three electron pairs
Bond order: the number of
Electron pairs that are shared between two atoms
Skeleton structure shows which atoms are
Bonded to each other in a molecule
Central atom: an atom bonded to
Two or more other atoms
Nonpolar
Equal sharing of electrons
Polar
Unequal sharing of electrons
The polarity of a compound can be determined by
Placing the compound in an electric field
If a molecule is polar it will no longer have a
Random orientation In the electric field
dipole moment is a measure of the
unequal sharing of electrons
the dipole moment of a compound can be determined by placing the compound in
an electric field
the unequal sharing leads to a … bond that is indicated with the symbol … followed by a sign to show …
polar covalent; δ; partial charges
electronegativity is the measure of the ability of an atom to attract the
shared electrons in a chemical bond
… is the most electronegative element
fluorine
electronegativity order of some elements
F>O>Cl=N
elements with low ionization energies have … electronegativities, and elements with high ionization eneries have … electronegativities
low; hgh
the polarity of a bond is proportional to the
difference in electronegativity between two covalently bonded atoms
electronegativities … across a period and .. down a row
increase; decrease
nonpolar electronegativity diff.
up to 0.4
polar electronegativity diff
0.4-1.7
ionic electronegativity diff
> 1.7
but to truly identify a substance as ionic, you must assess the
electrical conductance of the molten compound
formal charge is a charge assigned to atoms in lewis structures by assuming the shared electrons are
divided equally between the bonded atoms
formal charge =
v.e- - #lonepairelectrons - #bonds
lewis structures that show the …. formal chages are…
smallest; favored
lewis structures that have adjacent atoms with formal charges of the …. are …
same sign; much less favorable
lewis structures that place negative formal charges on the … are…
more electronegative atoms; favored
formal charges of opposite sign are usually on
adjacent atoms
resonance structures: structures that differ only in the
distribution of valence electrons
resonance is invoked when more than one valid Lewis structure can be
written for a particular moleucle
resonance bonds are … and …. than single bonds and … and …. than double bonds
shorter; stronger; longer; weaker
no resonance structure is correct by itself, the correct structure is
an average of all resonance structures
sometimes resonance structures are not equivalent, so … are used to determine which structure is favored
formal charges
four classes of molecules do not obey the octet rule:
electron-deficient; odd-electron; expanded valence shell; oxides & oxyacids
central atoms from groups … and … do not have enough valence electrons to complete an octet and are thus …
2; 3; electron-deficient
electron-deficiency is typically seen with compounds containt
Be, B, Al
any molecule that has an odd number of valence electrons must
violate the octet rule
odd-electron molecules are highly …, and are called …
reactive; radicals
in the lewis structure of a molecule that contains an odd number of electrons, one atom has only
seven valence electrons
expanded valence shell molecules have … about an atom in a lewis structure
more than eight electrons
a large class of expanded valence shell compounds have the general formula …, where Y= …
YFn; P, S, Cl, As, Se, Br, Te, I, or Xe
when more electrons are available than are needed to satisfy the octet rule for all atoms present, place the extra electrons around the
central atom as lone pairs
the octet rule can be exceeded for elements in … and … periods, but not for elements in the
third; later; second period
the octet rule is based on the idea that the valence s and p subshells can hold eight electrons, but atoms in the third and later periodshave …tat can hold ….,exceeding an octet
d subshells; additional electrons
oxides and oxyacids of p-block elements in periods …. typically have …
> = three; expanded valence shells
oxyacids have at least one … attached to an …. and has the general formula
hydrogen atom; oxygen atom; (HO)mXOn
species with strong bonds are generally
stable
bond dissociation energy (D) is the energy required to
break one mole of bonds in a gaseous species
bond energies are always …
endothermic
bond energies for diatomic molecules are measured …., other bond energies are …
directly; averages
triple bonds are … than double bonds which are … than single bonds
stronger; stronger
triple and double bond lengths are … than single bond lengths
shorter
ΔHreaction=
ΣDbondsbroken - ΣDbondsformed
breaking bonds always
requires energy
forming bonds always
releases energy
to calculate ΔHreaction, the lewis structures need to be written to determine the
types and numbers of bonds broken and formed
in calculating, ΔHreaction …. are used
average bond energies
bond order=
bonds/how many regions of bonding
for compounds, formal charges must add to
0
for polyatomic ions, formal charges should add to the
charge of the ion
(electronegativity) F=
4.0
(electronegativity) O=
3.5
(electronegativity) N=
3.0
(electronegativity) C=
2.5
(electronegativity) Cl=
3.0
(electronegativity) H=
2.1
(electronegativity) Br=
2.8
(electronegativity) I=
2.5
(electronegativity) S=
2.5
(electronegativity) P=
2.1
(electronegativity) Si=
1.8
(electronegativity) Al=
1.5
ionic compounds form from
metals and nonmetals;
nonmetal nonmetal compounds are usually
covalent bonds
