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