chem exam 4

waves with longer wavelengths have _______ frequencies and energies

lower

waves with shorter wavelengths _______ frequencies and energies

higher

light can behave like a wave or a collection of particles called

photons

shows how the energies, frequencies, and wavelengths of all types of light compare to each other

electromagnetic spectrum

visible light (lower energies) are _______ radiation and don’t hurt us 

nonionizing 

UV radiation (higher energies) are ________ radiation and damage our DNA

ionizing 

assumed circular electron orbits at fixed distances from the nucleus based on physics 

• electrons must be in a specific orbital that is assigned an ‘n’ value 

• energy levels get closer together as the distance from the nucleus gets larger 

• absorbed energy excites an electron and promotes it to a higher energy level, the electron must lose the energy or relax to its original level 

bohr model 

fixes the Bohr model flaw by stating that electrons exist in probability spaces around the nucleus 

quantum mechanical model 

cannot predict emission spectra for any atom that has more than one electron 

bohr model flaw 

energy level and distance from nucleus

n

shape

L

number of each orbital shape (-L to +L)

M_I

electron spin (+ or -1/2)

M_s

L = 0, s orbital

one circle

L = 1, p orbital

two circles

L = 2, d orbital 

four circles 

an orbital can only hold two electrons with opposite spins 

pauli exclusion 

when orbitals contain multiple subshells, sill each subshell with oneaelectron first then pair 

hunds rule 

fill orbital from lowest to highest energy

Aufbau princple

the distance from the nucleus to the valence electron when the element is part of an ionic compound

ionic radius 

distance from the nucleus to the valence electrons 

• decreases across a period (→) because the n value stays the same but the positive charge increase which attracts negatively charged electrons

• increases down a group because the n value increases, so average distance from the nucleus increases 

atomic radius 

the tendency of an atom to hold onto electrons when it is bonded to another atom. Atoms with hight ionization energies tend to have high electronegative when bonded. increases across a period and decreases down a group 

electronegativity 

characterized by
electron transfer from a metal to a
nonmetal or polyatomic ion, forming
cations and anions that alternate in a
crystal lattice

ionic bonding

characterized by electrons that are shared between two atoms; covalently bonded substances form discrete molecules

covalent bonding 

Some covalent bonds contain unevenly shared electrons

polar covalent bonds

bonding is based on sharing electrons so that each atom participating in a bond has a full valence shell (or as close as possible

lewis structure 

this theory states that bonds form due to orbital overlap, which increases the electron density between atoms. Electrons and bonds are localized, which means they belong to specific atoms and exist in specific places. Molecular shapes matched experimental evidence much better than Lewis theory

valence bond theory 

his theory is the most rigorous and states that bonds are combinations of atomic orbitals that form new molecular orbitals that either stabilize or destabilize the molecule when filled. It predicts energy and fractional bond orders well
and is best for fully describing molecules

molecular orbital theory 

It’s not great at predicting energy, and it can’t properly explain why some bonds aren’t
neatly classified as single, double, or triple bonds

valence bond theory flaw 

It doesn’t explain how bonding occurs, and structures don’t always match
experimental data

lewis structure flaw

atoms obtain a noble gas configuration when they have eight total valence electrons (fill both s and p orbitals)

octet rule 

this applies to hydrogen, which can only hold two total electrons, filling its s orbital

duet rule 

an electron bookkeeping system that is useful when drawing Lewis structures because it helps determine if the correct or most valid structure has been drawn

formal charge

number of valence electrons – number of electrons (dots) on the atom in the structure – number of bonds to the atom

formal charge equation

the central atom has 10 or 12 valence electrons around it instead of eight but it must be from period 3-7

expanded octet

this is only for boron. It has three valence electrons, so it typically forms only three covalent bonds

electron deficient 

a molecule with an odd number of valence electrons. This means they can’t all be paired, so there will be one unpaired electron on the central atom, or the atom with the lowest electronegativity

free radical 

theory determines shape by placing electron groups as far apart as possible around the central atom 

valence shell electron pair repulsion (VSEPR)

the polarity of molecules is based on both the polarity of the ________ and the molecules ______

bonds, shape

The type of bond formed can be predicted
using the ____________ difference
between the bonded atoms

electronegativity 

in general, atoms that are ____ _____ on the table have high electronegativity differences

far apart 

vectors, which mean they have magnitude (size) and direction, the size of this is determined by experiment. It can be estimated using electronegativity values

dipole moment 

the attractive forces among particles in a
sample

intermolecular forces

weak strength because the dipole is not permanent, but increases with increasing molar mass

• present in all atoms and molecules

dispersion forces (London force)

moderate strength, only in polar molecules 

dipole-dipole force

strong strength, only in molecules where H is bonded to F, O, or N

hydrogen bond

tendency for an atom’s electron density to shift and depends on the force of an electron between the nucleus and valence electrons 

polarizability 

larger molecules/atoms are ___ polarizable than smaller molecules/atoms because the outer electrons in bigger particles aren’t held tightly by the nucleus 

more

the polarizability and boiling points of
substances generally ______ as molar
mass increases

increase

a long hydrocarbon chain will
have a ______ polarizability and boiling
point than a branched structure, even if
they have the same molar mass because long chains have more contact points 

higher 

polar molecules have _____ melting/boiling
points (in general) than molecules with only
dispersion forces

higher

electrostatic potential maps show the distribution of ________ in molecules

electrons 

even distribution

green

negative end

red

positive end

blue

_______ melting/boiling points (in general)
than substances with no hydrogen
bonding

higher

covalent compounds ____ ______
when they dissolve, while ionic compounds
separate into ions

stay intact

measure of the thermal energy in a sample

temperature

thermal energy transfer from one substance to another due to a temperature difference

heat

Energy moves from ______ objects
to _______ objects until they reach
thermal equilibrium, which means
their temperatures are the same

warmer to cooler

the amount of energy needed to raise the
temperature of one gram of substance by 1°C and is an intensive property

specific heat capacity 

Substances with _____ specific heat
capacities resist temperature
changes more than substances with
______ specific heat capacities. More
energy must be absorbed to
increase the temperature of a
substance with a high specific heat
capacity

high, low

in general, substances with strong
IMFs have ______ specific heat
capacities than substances with
lower IMFs

higher

q

heat

m

mass

c (normally in J/g°C)

specific heat capacity

ΔT

temperature change

Intermolecular forces hold molecules together and must be broken by adding ______ to change a substance from a solid to a liquid or a liquid to a gas

energy

the energy needed to convert one mole of a substance from a solid to a liquid or a liquid to a gas

molar heats of fusion and vaporization