CHEM 2070 Prelim 2

negative enthalpy

heat flows out to surroundings, exothermic, forming bonds releases heat

positive enthalpy

reaction absorbs heat from surroundings, endothermic, breaking bonds absorbs heat

state function

a property that depends only on the current state of the system, not how it got there

examples of what is NOT a state function

heat and work

what to do with a state function problem when the reaction is reversed

flip the ΔH sign

Hess’s law

enthalpy change of a reaction is the sum of the enthalpy changes of the steps into which the reaction can be divided

bond enthalpy

enthalpy change with breaking a particular bond in a gaseous substance

speed of a wave

𝜆v

where are the nodes on a standing wave

locations with 0 amplitude

where are the antinodes on a standing wave

locations with maximum amplitude

photoelectric effect

electrons are only released if intensity is at a certain level

energy of a particle equation

1/2mv²

wavelength of a particle equation

𝜆=h/(mv)

energy of light from orbitals

E_light=hv= E_{orbit i} - E_{orbit f}

what happens when atoms go back down from being excited to a higher n state?

they emit light, different spectral line for each possible transition

photon energy in relation to work function and kinetic energy

E_photon= ɸ + KE = hc/lambda

Born rule

the square of the wave squared gives the probability density of finding the electron at a given location

Heisenberg uncertainty principle

the more precisely we know the position of a particle, the less precisely we can know it’s momentum and vice versa

radial nodes direction

towards/away from the nucleus

angular nodes direction

around the nucleus

what happens to the energy of an electron with more nodes

higher energy

shape of s orbitals

spherical

shape of p orbitals

dumbbell shape, 3 possible

shape of d orbitals

cloverleaf, 5 possible

shape of f orbitals

complex, 7 possible

what does n mean in electron configuration, and what are its possible values?

principle quantum number, number of radial nodes. 1, 2, 3…

what does mean in electron configuration, and what are its possible values?

azimuthal quantum number, number of angular nodes. from 0 to n-1

what does ml mean in electron configuration, and what are its possible values?

magnetic quantum number, orientation of angular wave. from -l to l. the number of possible orientations of orbitals equal 2l+1

what does ms mean in electron configuration, and what are its possible values?

spin quantum number, +1/2, -1/2

what happens to the + or - symbol when you cross a node

phase change (Switch from + to -)

what does the orbital look like when the spherical coordinates are squared

the orbital lies on the axes (specific to d orbitals?)

what do the spherical coordinates mean when they aren’t squared?

the orbital lies between the axes (if there are multiple)

subshell

set of orbitals with same n and l

shell

set of orbitals with same quantum number n

pauli exclusion principle

no two electrons in an atom can have the same set of quantum numbers, each orbital can hold at most 2 electrons which must have opposite spins

Hund’s rule

electrons fill degenerate orbitals singly before pairing up, all unpaired electrons have the same spin. because orbital is in it’s lowest energy state when the number of electrons with the same spin is maximized

Aufbau principle

electrons are added to the lowest energy orbitals available

how does the energy of multi-electron atoms change with increasing n and l

the energy increases

why do some elements have anomaly electron configurations?

Because s and d shells can be close in energy and half-filled and fully filled subshells are particularly stable

what electrons should you count for the “other electrons in same group” part of Slater’s rules for nd or nf shells

only count subshell in question. for ns or np count the other subshells with same n

what are the valence electrons

all electrons with same highest n in the atom’s electron configuration

what electrons should you remove first?

from the outermost shell (highest n number)

what electrons should you remove first from transition metals?

lose highest ns electrons before inner (n-1)d

what are the limitations of this formula used for hydrogen-like atoms (with 1 electron) E_n= -hcR_Hz2n2

can’t capture transitions inside a shell, not all electric transitions are possible

work function

minimum energy required to remove electrons from a material

how does the work function change as Zeff increases?

work function increases with Zeff

ionization energy

required to remove an electron (always +)

how does the ionization energy of an anion with -1 charge relate to the electron affinity of a neutral atom?

Ionization energy of an anion with -1 charge is the opposite of the electron affinity of a neutral atom

how does ionization energy change across a period

increases across a period

how does ionization energy change down a group?

decreases down a group

how does ionization energy change across transition metals? Why?

increases slowly across transition metals. added protons to the nucleus almost completely counteracted by the increased shielding of the d shell

how do elements with low ionization energy behave?

lose electrons, good conductors

how does atomic radius change across the periodic table?

decreases up a group and to the right. effects down a group are more significant across a period. because atoms are more attracted to the nucleus toward the top right

electron affinity

how much energy is released when an electron is added to an atom (negative)

if the electron affinity is negative, is the anion or neutral atom + free electron more stable?

the anion is more stable and lower energy than the neutral atom + free electron. A + e- —> A-

does removing an electron absorb or release energy?

always absorbs energy

alkali metals

very reactive, lowest IE, low Zeff

what is the exception to normal alkali metal behavior?

hydrogen. high IE, forms +1 cations and -1 anions

alkaline earth metals

less reactive than alkali

chalcogens

group 16

halogens

group 17, most reactive nonmetals

what changes in reactivity when a solid metal displaces another metal’s ions from solution?

If a solid metal displaces another metal's ions from solution, the solid metal is more reactive than the metal in the ions

what are the 3 quantities used in the Born-Haber cycle?

enthalpies of formation, ionization energies, electron affinities

how to set up lattice enthalpy equation when given enthalpy of formation?

set given enthalpy of formation to the sum of all the other components including lattice energy

what should be the sum of all oxidation numbers in a neutral molecule?

0

what is it called when the oxidation number of a element increases through a reaction?

oxidized, reducing agent

what is it called when the oxidation number of a element decreases through a reaction?

reduced, oxidizing agent

what defines a hydrogen-like atom?

only 1 electron, regardless of amount of protons

what kind of node can be shown on the radial probability function graphs?

radial nodes, don’t know about angular nodes

where does the radial probability graph start for a s orbital?

above zero

where does the radial probability graph start for a p, d, or f orbital?

at zero

how to determine the number of radial nodes from quantum numbers?

Radial nodes= n - l - 1

what transitions between orbitals are allowed?

change in l and m_^l must be +-1

what quantum number represents number of angular nodes?

l

do cations increase or decrease atomic radius?

decrease

do anions decrease or increase atomic radius?

increase

which atom has a larger atomic radius if both have the same number of electrons?

the one with more protons is smaller, more attraction at the nucleus