Quantum Theory and the Electronic Structure of Atoms Flashcards
Max Planck
-discovered that atoms and molecules emit energy only in certain discrete quantities (QUANTA)
-Quantum theory
Classical physics
-energy is continuous and that any amount of energy could be released in a radiation process
-assumed that atoms and molecules could emit or absorb any arbitrary amount of energy
Wave
-vibrating disturbance by which energy is transmitted
-periodic: wave form repeats itself at regular intervals
Wavelength, λ
-distance between identical points on successive waves
Frequence, f
-number of waves that pass through a particular point in one second
1 Hz = 1 cycle/s
Amplitude
-vertical distance from the midline of a wave to the peak or trough
Wave speed, v
-depends on the type of wave and the nature of the medium through which the eave is travelling
v = λ.f
James Clerk Maxwell (1873)
-visible light consists of electromagnetic waves
•Electromagnetic wave- has electric field component and magnetic field; these components have same frequency, wavelength, speed but travel in mutually perpendicular planes
-speed of electromagnetic waves: speed of light
Electromagnetic radiation
-emission and transmission of energy in the form of electromagnetic waves
Gamma rays
-electromagnetic radiation
-shortest wavelength; highest frequency
Radio waves
-electromagnetic radiation
-longest wavelength; lowest frequency
Visible light
-electromagnetic radiation
-wavelength: 400 nm (violet) - 700 nm (red)
⬆️ Frequency ⬆️ Energy
Solids are heated ➡️ emit electromagnetic radiation
Electric heater: dull red
Tungsten light bulb: bright white light
Quantum
-smallest quantity of energy that can be emitted/ absorbed in the form of electromagnetic radiation
-energy of single quantum:
E =h.f
-(Quantum theory): energy is always emitted in multiples of hf (i.e. hf, 2hf, 3hf but not 3.98hf, 1.67hf)
Albert Einstein (1905)
used quantum theory for:
•PHOTOELECTRIC EFFECT
-electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency (threshold frequency)
-no. of electrons ejected proportional to intensity (brightness) of light
-below threshold frequency, no electrons ejected no matter how intense the light
-electrons in metal are held in attractive forces; removing requires light of sufficiently high frequency (~high energy)
Photons- a beam of light is a stream of particles; each photon contains energy
E = h.f
Photoelectric effect formula
hf = KE + BE
KE: Kinetic energy of ejected electron
KE = 1/2 .me. v^2
me: mass of electron
BE: Binding energy of electron in metal
f < fthres : no electron ejected
f = fthres : only knock the electrons loose
f > fthres : electrons knock loose with kinetic energy
-more intense beam of light, larger number of protons: more electrons ejected
-higher frequency of light, greater kinetic energy of emitted electrons
Isaac Newton
-sunlight is composed of various color components that can be recombined to produce white light
Emission spectra
-either continuous or line spectra of radiation emitted by substance
-seen by energizing sample material with thermal energy or some other form of energy
-every element has a UNIQUE emission spectrum
Line spectra
-light emission only at specific wavelength
-emission spectra of atoms in gas phase: do not show continuous spread of wavelengths from red to violet
Niels Bohr (1913)
-emission spectrum of hydrogen atom
-each orbit has a particular energy associated with; energies associated with electron motion in the permitted orbits must be fixed in value or QUANTIZED
-emission of radiation by energized hydrogen atom: associated with electron dropping from higher-energy orbit to a lower one, giving up a quantum of energy (photon) in the form of light
En = -R(1/n^2)
En: energy of electron; n: principal quantum number (1,2,3,4 etc)
Convention: (-) energy of electron in atom is lower than energy of free electron (far from nucleus)
•Free electron: E∞=0
•Electron gets closer to nucleus (n decreases): En = more negative
Ground state/ ground level
n=1
-lowest energy state of a system
Excited state/ excited level
n = 2, 3, 4…
-higher energy than in ground state, less tightly held by nucleus
⬆️ n (farther from nucleus) ⬇️ stability
Rydberg’s formula
∆E = hf = R(1/ni^2 - 1/nf^2)
ni > nf : photon is emitted (-∆E: energy released)
ni < nf : (+∆E: energy absorbed)