Chapter 7

Question 1

wavelength(λ)

Answer 1

• the distance from crest to crest or trough to trough on a wave
• c=λv

Question 2

frequency(v)

Answer 2

• the number of crests of a wave that pass a stationary point of reference per second
  
  • cycles per second
• c=λv
  
  • c=spped of light=3x10⁸

Question 3

electromagnetic properties of radiant energy

Answer 3

• when electromagnetic properties of radiant energy pass through air, it interacts with fewer atoms than thru solids or liquids
  
  • more interactions btwn the oscillating waves and the electrons within the atoms and molecules in solids and liquids slow the waves and bend their paths
    
    • shorter wavelengths bend more than long ones which is why violet is at the bottom of rainbows

Question 4

quantum theory

Answer 4

• quantum theory: a model based on the idea that energy is absorbed + emitted in discrete quantities of energy(quanta)
  
  • the smallest discrete quantity of a particular form of energy
• Planck proposed that light and all other forms of electromagnetic radiation have not only wavelike properties, but also particle-like properties on the atomic level.
• Light from an object made of large, but discrete #s of atoms or molecules must be quantized
  
  • having values restricted to whole# multiples of a specific base value
  • steps are quantized while a ramp is continuous
• A quantum of light(EM radiation) is called a photon

Question 5

photoelectric effect

Answer 5

• the phenomenon of light striking a metal surface and producing an electric current(a flow of e^-)
  
  • electrons are emitted from metals when they are illuminated by and absorb electromagnetic radiation

Question 6

threshold frequency(v₀)

Answer 6

• the minimum frequency of light required to produce the photoelectric effect.
• radiation at frequencies less than the threshold value produces NO photoelectrons aka if incoming light has v<v>0
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  <li>even a dim source of radiant energy produces at least a few phtoelectrons when the frequencies it emits are equal to or greater than v₀
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* Einstein proposed the threshold frequency of the minimum quantum of absorbed energy needed to remove a single electron from the surface of

Question 7

work function (𝛟)

Answer 7

• the amount of energy needed to remove an electron from the surface of a metal
  
  • 𝛟 = hv₀
• If a photoelectric material is illuminated with radiation frequencies above threshold frequency(v>v₀), any energy in excess of 𝛟 is imparted to each ejected e- as KE
  • extra energy = KE of emitted electrons
  • KE_electron=hv-hv₀=hv-𝛟
  • E_photon=𝛟+KE_electron
  • the higher the frequency is above the threshold, the higher the KE and hence the velocity of ejected e-

Question 8

wave-particle duality

Answer 8

• thebehavior of an objectthat exhibits the properties of both a wave and a particle

Question 9

the hydrogen emission spectrum

Answer 9

• Balmer determined lines corresponding to the visible emission spectrum of hydrogen fit the simple equation:
  
  • λ = 364.5 nm(m²/m²-n²)
  • n is 2 and m is whole# >2

Question 10

Rydberg’s equation

Answer 10

• revised Balmer’s eqn(made a more general form)
  
  • 1/λ = 1.097x10^-2nm^-1
    
    • n₁ is a postive fixed whole number
    • n₂ is a whole number equal to n₁+1, n₂+2….

Question 11

the Bohr model of hydrogen

Answer 11

• a theoretical model for the hydrogen atom that assumed its one electron travels around the nucleus in a concentric orbit. Electrons can only exist in these discrete orbits. Each orbit represents an allowed energy level and is designated by the value of n as shown in
  
  • E = 2.178 x 10^-18J(1/n²)
  • in the bohr an electron in the orbit closest to the nucles(n=1) has the lowest energy
  • lines in the absorption and emission spectra represent electrons moving btwn energy levels(orbits)

Question 12

ground+excited state

Answer 12

• ground state: when the e- in a hydrogen atom is in the lowest (n=1) energy level
  
  • most stable
• excited state: if the electron in a hydrogen atom is above n=1 energy level
• hydrogen atom’s e- can move from ground to excited state(up energy level) it absorbs a quantity of energy(deltaE) that exactly matches the energy difference btwn the two excited states
• electron transition: any change in e- energy that occurs by absorption or emission of energy
  
  • movement of an e- btwn energy levels

Question 13

De Broglie Wavelengths

Answer 13

• Light is a wave that has particle properties and an electron is a particle which must have wave properties
  
  • this would mean electrons moving in atoms should have a wavelength
  • De Brolgie wavelength: λ = h/mv
    • m is momentum, a particle property
    • λ is wavelength, a wave property
  • λ = h/mu
    
    • m is mass in kg
    • u is velocity in m/s
• not restricted to electrons

Question 14

classical and quantum mechanics

Answer 14

• classical mechanics(Newton)
  
  • good for large objects
  • not good for atoms, electrons, etc
• the issue: chemistry occurs at the atomic level
  
  • solution: Quantum mechanics: combines both wave and particle aspects of matter into a unified theory

Question 15

nodes

Answer 15

• a location in a standing wave that experiences no displacement
  
  • In the context of orbitals, nodes are locations at which electron density goes to zero

Question 16

standing wave

Answer 16

• a wave confined to a given space, with a wavelength (λ) related to the length L of the space by L 5 n(λ/2), where n is a whole number.

Question 17

matter wave

Answer 17

• the wave associated with any particle

Question 18

Heating a blackbody

Answer 18

• Blackbody radiation(heated objects emit EM radiation): classical theory does not match observations
  
  • explanation: electromagnetic radiation has particle-like properties in addition to wavelike properties

Question 19

The Heisenberg Uncertainty Principle

Answer 19

• the principle that we cannot determine both the position and the momentum of an e- in an atom at the same time
  
  • since we can’t know both position and momemntum of an e- in a hydrogen atom, the e- cannot be moving in circular orbits as implied by Bohr’s og model.
  • Heisenberg uncertainty principle limits us to knowing only the probability of finding an electron at a particular location in an atom
• (∆x)(∆mv) ≥ h/4π
  • ∆x = uncertainty in position
  • ∆mv = uncertainty in momentum

Question 20

wave mechanics aka quantum mechanics

Answer 20

a mathematical description of the wavelike behavior of particles on the atomic level

Question 21

Schrodinger wave equation

Answer 21

• a description of how the e- matter wave varies with location and time around the nucles of a hydrogen atom
  
  • wave function(𝛙): a solution the the Schrodinger wave eqn
    
    • Mathematical expressions that descrive how the matter wave of an e- in an atom varies both with time and with the location of the e- in the aotm
    • wave functions define energy levels in H atoms
    • 𝛙 ² defines an orbital
      • ​aka probability of finding an e-

Question 22

orbital

Answer 22

• a region around the nucleus of an atom where the probability of finding an e- is high; each orbital is defined by 𝛙 ² and identified by a unique combination of 3 quantum #s

Question 23

quantum number/principle quantum number(n)

Answer 23

• a number that specifies the energy, the probable location or orientation of an orbital, or the spin of an electron within an orbital(ALL quantum numbers are integers)
  
  • principle quantum number(n): a positive integer describing the relative size and energy of an atomic orbital or group of orbitals in an atom
    
    • same as Bohr’s n
    • orbitals with same n are in same shell
    • as n increases, orbital size increases and e- are further from nucleus and, in the H atom, represent higher energy levels
      
      • generally, this is also true in multielectron atoms

Question 24

angular momentum quantum number(l)

Answer 24

• an integer having any value from 0 to n-1 that defines the shape of an orbital
  
  • orbitals with same n and l are in same subshell and have equal energy levels
    
    • l=0 → s
    • l=1 → p
    • l=2 → d
    • l=3 → f

Question 25

magnetic quantum number(m_l)

Answer 25

* an integer with a value from -l to +l. It defines the **3d orientation** of an orbital in the space around the nucleus of an atom

Question 26

spin magnetic quantum number(m_s)

Answer 26

* either +1/2 or -1/2, indicating that the spin orientation of an e- ie either up or down

Question 27

Pauli exclusion principle

Answer 27

* the principle that no two e- in an atom can have the same set of four quantum numbers * therefore, each orbital can hold two e- with opposite spins

Question 28

aufbau principle

Answer 28

* states the most stable atomic structures are those in which the e- are in the lowest-energy orbitals available * Three rules: * 1) e- always go into lowest-energy orbital available * 2)each orbital can hold up to 2 e- with opposite spins(Pauli) * 3) for degenerate orbitals, e- fill each orbital singly before pairing up (Hund)

Question 29

effective nuclear charge (Z_eff)

Answer 29

* the attraction toward the nucleus experienced by an e- in an atom, equal to the positive charge on the nucleus redfuced by the extent to which other e- in the atom shield the e- from the nucleus

Question 30

core electrons

Answer 30

* e- in the filled, inner shells of an atom or ion that are not incolved in chemical rxns

Question 31

valence electrons

Answer 31

* e- in the outermost occupied shell of an atom * these are the e- that are transferred or shared in chemical rxns

Question 32

valence shell

Answer 32

the outermost occupied shell of an atom

Question 33

degenerate(orbitals)

Answer 33

describes orbitals of the same energy

Question 34

Hund's rule

Answer 34

* the lowest-energy electron configuration of an atom has the maximum number of unpaired electrons, all of which have the same spin, in degenerate orbitals * this is the third rule we apply when doing e- configuration

Question 35

isoelectronic

Answer 35

* atoms or ions that have identical e- configurations and identical # of e- * **increasing nuclear charge(Z_eff)** corresponds to **smaller ions**

Question 37

Periodic trends

Answer 37

* As atomic # increases, atomic radii increases(aka as we move right and down) * As we move towards the right, each successive element has one additional e-, so we expect an inc. in size of atom * this isn't true because: * 1) **increasing Z_eff**: as atomic # inc, so does positive charge of the nucleus * as Z_eff inc, the size of atoms dec. * 2) **increasing repulsion btwn valence e-:** as atomic # inc, so does # valence e- * more e- = more electron-electron repulsions(b/c two negs repel), which inc size of atoms

Question 38

Ionization energy(IE)

Answer 38

* the quantity of energy needed to remove 1 mole of electrons from 1 mole of ground-state atoms or ions in the gas phase * doing so always requires energy entering system b/c a negatively charged e- is attracted to a positively charged nucleus, and overcoming that attravtice force requires energy * the amount of energy needed to remove 1 mole of e- from 1 mole of atoms to make 1 mole of cations with a 1+ charge is called the **first ionization energy(IE₁)** * **​**generally inc as we go towards the right and up * ​easiest element to ionize is group 1 * this pattern makes sense b/c as the charge of a nucleus inc. across a row, so does Z_eff and the attractions btwn nucleus and valence e- * the amount of energy needed to remove 1 mole of e- from 1 mole of 1+ cations to make 1 mole of cations with a 2+ charge is called the **second ionization energy(IE₂)** * **​total IE = IE₁+IE₂**

Question 39

electron affinity (EA)

Answer 39

* the energy change that occurs when 1 mole of e- combines with 1 mole of atoms or monatomic cations in the gas phase * the EA of many elements are negative b/c the formation of anions with a 1- should release energy * can be endothermis or exothermic * very large negative EA means it is favorable to form the anion * **Trends:** * EA increases going down * generally, EA becomes more negative(decreases) when going right(as atomic# inc) * the halogens of group 17 have the most negative(lowest) EA values