Chapter 3.1-3.2

Question 1

What is a wave?

Answer 1

Light behaves as a wave

You can calculate it

Question 2

Wave Characteristics

Answer 2

Speed of light (c): 2.998x10^8 m/s

Wavelength: the distance from one peak to the next

Frequency (v): is the number of wavelengths (“cycles”) that pass a point in a given period of time

Amplitude: 1/2 the height between peaks & throughs

Question 3

electromagnetic spectrum

Answer 3

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

Question 4

How do we know light acts as a wave?

Answer 4

a) Constructive interference

b) Destructive interference

Waves bend around and encounters an obstacle slit that is about the same size of the wavelength is diffreacts (think about a light curve under a closed door)

Question 5

Diffraction Definition

Answer 5

The scattering of photon waves by an object such as an electron cloud, resulting in constructive or destructive interference

Question 6

Standing Waves

Answer 6

waves constrained in some particular region of space

-can have only a half-integer # of wavelengths

-Standing waves exhibit nodes: places where the amplitude remains zero

-As the energy increases, so does the # of wavelengths & the # of nodes

Question 7

Blackbody Radiation

Answer 7

-The emission of photons over a broad and continuous range of
wavelengths

Substances produce a continuous spectrum when heated
Objects array different temperatures

-As temp increases, total intensity increases, max wavelength increases

-1900 Max Planck proposed that the energy of light came in discreet “chunks”: light is quantized

h (Planck’s constant) = 6.626x10^-34

Question 8

Photoelectric Effect

Answer 8

-1902: Philip Kenard found three rules for the photoelectric effect

1. No electrons are emitted unless the light has a frequency above a threshold, which varies for different metals
2. Electrons are ejected immediately

Finish

Question 9

Einstein’s Explanation

Answer 9

• Light energy was delivered to the atoms in packets called photons, with energy (E)
• One photon at the threshold frequency has just enough energy for an electron to escape the atom
• High frequencies: electron absorbs more energy, excess energy becomes kinetic energy of the ejected electron

Question 10

The wave-particle Duality of Light

Answer 10

Light behaves like both a wave..
-has a speed, wavelength, frequency
-exhibits interference and diffraction

… and like a particle

-blackbody radiation, Finish

Question 11

Line spectra

Answer 11

-When atoms absorb energy (heat, electrical current),
that energy is often released as light

-When that light is passed through a prism, a pattern is seen that is unique to that type of atom: atomic emission spectrum

-The light is emitted only at a few specific wavelengths: line source or line spectrum

Question 12

Atom spectrum of Hydrogen

Answer 12

• 1885: Balmer noted that wavelengths of the lines in the visible spectrum of hydrogen followed by a simple formula

-1888: Rydberg created a general equation for the wavelengths of the line spectrum of hydrogen: Rydberg equation:

Question 13

Bohr Model of the Atom

Answer 13

1

Question 14

Wavelength as it relates to a electromagnetic

Answer 14

Wavelength is the distance between two consecutive peaks or troughs in a wave

Question 15

Color of light, frequency and wave length

Answer 15

Red light has a lower frequency and a longer wavelength than ultraviolet rays.

Ultraviolet rays has a higher frequency and a shorter wavelength than red light.

Question 16

Symbols and equations:

Answer 16

The speed of a wave (c)
frequency ν
wavelength λ
energy of a photon equals its Planck’s constant (h)

c=λν

E=photon energy

h=pats constant

E = hv

Answer 17

The energy (E) of a photon of light is proportional to its frequency (ν) or the inverse of its wavelength (λ) multiplied by Planck’s constant (h):

E=hu=hc/λ
As such, light with a lot of energy will have a high frequency and a small wavelength.

Question 18

Bohr Model

Answer 18

3. The energy of the electron was
   proportional the distance the orbit
   was from the nucleus: energy of
   electron is quantized
4. The atom emitted a photon when the electron “jumped” from an orbit
   with higher energy down to an orbit with lower energy
5. If the atom absorbed a photon of a certain freq., the electron “jumped”
   from an orbit with lower energy to an orbit with higher energy

Question 19

How does the Bohr Model work?

Answer 19

When an electron jumps among diff. orbits, energy is emitted or absorbed as photons✓ from larger n to smaller n: photon emission
✓ opposite is photon absorption
✓ n is the principal quantum number
✓ Joule (J) is the SI unit for energy
➢ 1 J = 1 kg m2/s2

Question 20

Bohrs model and Liberge equation

Answer 20

Bohrs model finds the awnser to the Liberge equation:

Question 21

What falts does the Bohr Model have?

Answer 21

1. It violates basic laws of physics (an electrically charged
   particle orbiting in a circular path should lose energy, so the
   electron should eventually spiral into the nucleus)
2. It fails to explain the line spectra of any elements other than
   hydrogen

Question 22

What new Ideas did the Bohr Model introduce?

Answer 22

Nonetheless, the Bohr model introduced some key ideas:
1. Energies of electrons in atoms are quantized, given by
quantum numbers
2. An electron’s energy increases with increasing quantum
number and thus distance from the nucleus
3. The discreet line spectra of elements result from transitions
between these quantized electronic energy levels of atoms

Question 23

Wave Nature of Matter

Answer 23

1925: de Broglie proposed that electrons (like photons) were both particles & waves
✓ de Broglie wavelength

• 1927: Davisson and Germer showed that electrons exhibit diffraction

• De Broglie said the electroons were standing waves

Answer 24

When you try to observe a photons location it starts to act like a partical instead of a wave

Question 25

Heisenberg’s Uncertainty Principle

Answer 25

1927: Heisenberg’s uncertainty principle: “If a measurement of position is made with precision x and a simultaneous measurement of momentum is made with precision p, then the product of the 2 uncertainties must be ≥ h/4p.”

• This has nothing to do w/ imperfections in our measurement abilities: it

Question 26

Does the orbital in the bohr model impact the energy level

Answer 26

The higher the orbital the higher the energy level

Question 27

work function

Answer 27

is the energy that must be supplied to cause the release of an electron from a photoelectric material. The corresponding photon frequency is the threshold frequency. The higher the energy of the incident light, the more kinetic energy the electrons have in moving away from the surface.

Question 28

What does ψ² discribe?

Answer 28

While the wave function ψ describes the overall state of a quantum system, the square of the wavefunction (ψ2) gives the probability of finding an electron in a given region of space.

Question 29

Memorize

Answer 29

Atomic orbitals are described by their principal quantum number (n) followed by a letter that corresponds to the value for the angular momentum quantum number (ℓ). Here, n= 3, so the atomic orbital symbol will begin with 3. The quantum number p = 1 (s = 0, p = 1, d = 2, f = 3), which corresponds to p. Therefore, this is a 3p atomic orbital.