CHM1045 - Exam 4
octet rule exceptions
-Hydrogen (has only 2) -Lithium, Beryllium, and boron (less than 8) -all period 3 and below can hold >8
properties of solids
1. Definite Shape 2. Definite Volume 3.Does not expand 4. Has smallest molecule movement
properties of liquids
1. Takes shape of container 2. Definite Volume 3. Does NOT expand
linear electron geometry
2 electron groups, 180 degrees, sp
trigonal planar electron geometry
3 electron groups, 120 degrees, sp2
tetrahedral electron geometry
4 electron groups, 109.5 degrees, sp3
trigonal bipyramidal electron geometry
5 electron groups, sp3d •The positions above and below the central atom are called the axial positions •The positions in the same base plane as the central atom are called the equatorial positions •The bond angle between equatorial positions is 120° •The bond angle between axial and equatorial positions is 90°
octahedral electron geometry
6 electron groups, 90 degrees, sp3d2
crystal lattice
A 3-dimensional geometric arrangement of the atoms or molecules or ions composing a crystal; maximizes the attractions between cations and anions, leading to the most stable arrangement; electrostatic attraction is nondirectional! Therefore, there is no ionic molecule
covalent bond
A chemical bond that involves sharing a pair of electrons between atoms in a molecule; usually non-metal-to-non-metal
polar covalent bond
A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.
Hydrogen bonds
An especially strong dipole-dipole attraction results when H is attached to an extremely electronegative atom - F, O, or N
supercritical liquid
At some temperature, the meniscus between the liquid and vapor disappears and the states commingle to form a supercritical fluid, which has properties of both gas and fluids liquid states
electron geometry vs molecular geometry
Electron geometry- the geometrical arrangement of the electron groups Molecular geometry- the geometrical arrangement of the atoms
ionic bond
Formed when one or more electrons are transferred from one atom to another; usually metal-to-non-metal
N2H4
Hydrazine, colorless liquid weakly basic, powerful reducing agent
volatile
Liquids that evaporate easily
___________ energy atomic orbitals contribute more to the bonding MOs. ___________ energy atomic orbitals contribute more to the antibonding MOs. ___________ MOs remain localized on the atom donating its atomic orbitals.
Lower; higher, nonbonding
Boron
Metalloid; less than 0.001% in Earth's crust, but found concentrated in certain areas; used in glass manufacturing - borosilicate glass = Pyrex; used in control rods of nuclear reactors
Which element is 78% of the atmosphere by volume?
Nitrogen, N2
dipole-dipole forces
Permanent polarity in the molecules due to their structure leads to attractive forces
dynamic equilibrium
Result of diffusion where there is continuous movement of particles but no overall change in concentration
Pyrosilicate
Si2O7 6-
Pyroxene
SiO3 2-
Orthosilicate
SiO4 4-
octet rule
States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons
Electronegativity
The ability of an atom to attract bonding electrons to itself
heat of vaporization
The amount of heat energy required to vaporize one mole of the liquid
bent molecular geometry
The central atom is surrounded by 2 shared electron domains and 1 unshared electron domain. Derivative of Trigonal Planar Electron Geometry
Condensation
The change of state from a gas to a liquid; exothermic
Vaporization
The change of state from a liquid to a gas; endothermic
Meniscus
The curved upper surface of a liquid in a tube
Vapor pressure
The pressure exerted by the vapor when it is in dynamic equilibrium with its liquid. The weaker the attractive forces, the higher the vapor pressure and the more volatile the liquid.
Phyllosilicates
When 3 O of each tetrahedron are shared, the result is a sheet structure
bonding molecular orbital
When the wave functions combine constructively, the resulting molecular orbital has less energy than the original atomic orbitals s, p
antibonding molecular orbital
When the wave functions combine destructively, the resulting molecular orbital has more energy than the original atomic orbitals s*, p*
Derivatives of Tetrahedral Electron Geometry
When there are four electron groups around the central atom, and one is a lone pair, the result is called a pyramidal shape. When there are four electron groups around the central atom, and two are lone pairs, the result is called a tetrahedral—bent shape.
metallic bond
a bond formed by the attraction between positively charged metal ions and the electrons around them; bond between metals
Born-Haber cycle
a hypothetical series of reactions that represents the formation of an ionic compound from its constituent elements DH°f(salt) = DH°f(metal atoms, g) + DH°f(nonmetal atoms, g) + DH°f(cations, g) + DH°f(anions, g) + DH°(crystal lattice)
coal
a mixture of hydrocarbons and carbon- rich particles that comes from the carbonation of ancient plant material
dipole moment
a property of a molecule whose charge distribution can be represented by a center of positive charge and a center of negative charge
NH3
ammonia, pungent gas, basic
trends in bond length
as bonds get longer, they also get weaker
Electrons that are shared by atoms are called _________ pairs. Electrons that are not shared by atoms but belong to a particular atom are called _________ pairs.
bonding; lone
Heating wood in the absence of air forms what?
charcoal
Heating coal in the absence of air forms what?
coke
Soot
composed of hydrocarbons from incomplete combustion
Meniscus of Water vs Mercury
concave because adhesion > cohesion; convex because cohesion > adhesion
crystalline vs. amorphous solids
crystalline solids are arranged in a regular repeating pattern, eg. salt and diamonds amorphous have no certain pattern, eg. plastic and glass
bond order
difference between number of electrons in bonding and antibonding orbitals (# bonding electrons - # antibonding electrons)/2
dispersion forces (London dispersion forces)
dispersion is an intermolecular attraction force that exists between all molecules. These forces are the result of the movement of electrons which cause slight polar moments. Generally very weak, when their molecular mass increases, so does their strength
Better Lewis dot structures have _________ and _________ formal charges. Better structures also have the negative formal charge on the _________ electronegative atom.
fewer, smaller; more
activated carbon
finely divided charcoal formed by heating amorphous carbon in steam
Carbon black
finely divided form of carbon that is a component of soot
Desposition
gas to solid
Anthracite coal vs. bituminous coal
highest C content vs. high C and high S
HN3
hydrogen azide, weakly acidic
If difference in electronegativity between bonded atoms is larger than or equal to 2.0, the bond is ________.
ionic
Freezing
liquid to solid; exothermic
Which is denser: liquid water or ice?
liquid water
Nanotubes
long, thin hollow cylinders of atoms
properties of gases
low density, lots of empty space between particles; volume of space that gas particles take up, can be reduced by compressing particles together (assumption 1), fluid, spreads out to shape of container, no definite shape or volume (assumption 3 and 4)
Chemical bonds form because they _________ the potential energy between the charged particles that compose atoms.
lower
Fusion
melting/freezing
Aluminosilicates
members of a family of compounds in which aluminum atoms substitute for silicon atoms in some of the silicon lattice sites of the silica structure
Silicates
minerals that contain silicon and oxygen and usually one or more other elements; found in rocks, soils, and clays; SiO4, sp3 hybridization
NO2
nitrogen dioxide, red-brown gas
NO
nitrogen monoxide, colorless, reactive, slightly soluble in water, toxic
If the difference in electronegativity between bonded atoms is 0.1 to 0.4, the bond is _____________.
nonpolar covalent
What are the most abundant elements in Earth's crust?
oxygen and silicon
Today, the major source is heating the mineral apatite in an electric furnace with sand and coke to form ______________.
phosphorus
If difference in electronegativity between bonded atoms is 0.5 to 1.9, the bond is ______________.
polar covalent
Lewis structures allow us to _________________.
predict many properties of molecules, such as molecular stability, shape, size, polarity
If difference in electronegativity between bonded atoms is 0, the bond is ____________.
pure covalent
pi (p) bond
results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei -- between unhybridized parallel p orbitals
sigma (s) bond
results when the interacting atomic orbitals point along the axis connecting the two bonding nuclei -- either standard atomic orbitals or hybrids
Are sigma or pi bonds stronger?
sigma
Amphiboles
silicates with two chains bonded together at half the tetrahedra
Phases of water
solid (ice - 0 C), liquid (water - 20 C), gas (water vapor/steam - 100 C)
Sublimation
solid to gas
Melting
solid to liquid; endothermic
The higher the normal boiling point of the liquid, the __________ the intermolecular attractive forces.
stronger
resonance structures
structures that occur when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion
The average kinetic energy is directly proportional to the _____________.
temperature KEavg = 1.5 kT
capillary action
the ability of a liquid to flow up a thin tube against the influence of gravity - result of cohesive (holds molecules together) and adhesive forces (attracts molecules to the tube)
translational freedom
the ability to move from one position in space to another
vibrational freedom
the ability to oscillate about a particular point in space
rotational freedom
the ability to reorient the particles direction in space
formal charge
the charge assigned to an atom in a molecule or polyatomic ion derived from a specific set of rules FC = valence e− − nonbonding e− − ½ bonding e−
bond enthalpy
the energy needed to break one mole of bonds in gaseous molecules under standard conditions DHrxn = bonds broken (reactants) - bonds formed (products)
surface tension
the force that acts on the surface of a liquid and that tends to minimize the area of the surface. The stronger the intermolecular attractive forces, the higher the surface tension will be. Raising the temperature of a liquid reduces its surface tension
ion-dipole forces
the force that exists between an ion and a neutral polar molecule that possesses a permanent dipole moment
percent ionic character
the percentage of a bond's measured dipole moment compared to what it would be if the electrons were completely transferred (measured dipole moment of bond)/(dipole moment if electron were completely transferred) * 100%
Viscosity
the resistance of a liquid to flow - 1 poise = 1 P = 1 g/cm∙s - often given in centipoise, cP - Larger intermolecular attractions = larger viscosity - The more spherical the molecular shape, the lower the viscosity will be
Boiling point
the temperature at which the vapor pressure = external pressure
VESPR theory
valence shell electron pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electrons pairs are as far apart as possible
dipole moment equation
µ = qr - q = 1.6 * 10^-19 C (magnitude needed to separate a proton and an electron) - The debye (D) is the unit commonly used for reporting dipole moments; 1 D = 3.34 * 10^-30 C*m
Carbon
•Exhibits the most versatile bonding of all the elements •The crystalline forms include diamond, graphite, and the fullerenes •Diamond structure consists of tetrahedral sp3 carbons in a 3-dimensional array •Graphite structures consist of trigonal planar sp2 carbons in a 2-dimensional arrayCoal
Derivatives of the Trigonal Bipyramidal Electron Geometry
•When there are five electron groups around the central atom, and one is a lone pair, the result is called the seesaw shape •When there are five electron groups around the central atom, and two are lone pairs, the result is called the T-shaped •When there are five electron groups around the central atom, and three are lone pairs, the result is a linear shape
Derivatives of Octahedral Electron Geometry
•When there are six electron groups around the central atom, and one is a lone pair, the result is called a square pyramid shape •When there are six electron groups around the central atom, and two are lone pairs, the result is called a square planar shape
