AS.C5_chemistry notes
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Transcript of AS.C5_chemistry notes
Where did Rutherford leave us...
Ernest, we have a problem...• Rutherford’s model didn’t explainchemical properties
• Needed a new model
• Bohr proposed that electrons orbit in distinct energy levels
• Can’t be between levels, but can jump from one to another
• Quantum: amount of energy needed for an electron to jump from one energy level to anotherNiels Bohr
(1885‐1962)
What the…?
• Scientists found that they can’t base a
model for tiny little atoms on the
rules for normal‐sized stuff
• Atoms and subatomic particles act differently– Particles act like particles…and waves
– Double‐slit experiment…wow.
• Can only know (calculate) probability that electrons are at a given location
Atoms = ogres = neighbors = onions...
Quantum Mechanical Model: determines allowed energies an electron can have and where electrons are likely to be
Energy levels: “layers” where electrons – Numbered– Each one gets bigger than previous– Can have sublevels
Atomic orbitals: region in space in which there’s a high probability of finding an electron– In sublevels– Given letters
Sublevels and orbitalss sublevel
– one spherical orbital
– one in every energy level
p sublevel– three dumbell‐shaped orbitals
– in all energy levels ≥ 2
Sublevels and orbitals
d sublevel– five crazy shapes
– in all energy levels ≥ 3
f sublevel– seven shapes that are really too tough to draw
– in all energy levels ≥ 4
Back to the ogres/onions...
• Each energy level gets one more sublevel
Back to the ogres/onions...
• Each energy level gets one more sublevel
• Each energy level can hold more electrons
• Max of 2 e‐ / orbital
• # of e‐ = n2 x 2
Where do electrons live?
Electron’s address• Energy level
• Sublevel
• Orbital
• Spin
Your address• State
• Town
• Street
• House
Need a system for electron addresses...
Keeping track of all the sublevels• Sublevels addressed by the number of their energy level and letter of sublevel
Example: 1s, 2s, 2p, 3s, 3p, 3d
• Still two more parts to address (orbital and spin)...
Electron configuration: arrangement of electrons in an atom in its ground state
Orbital diagram: illustrates arrangement and spin of electrons
Rules for Electron Configurations
Aufbau principle: electrons occupy orbitals of lowest energy first
Electrons (like Jamarcus Russell) are lazy
Orbitals in same sublevel are same energy
Rules for Electron Configurations
Pauli Exclusion Principle• Orbital can hold maximum of two electrons
(Two per seat on the bus)
• If two electrons in an orbital, must be opposite spins
• Two possible spins: up and down– clockwise and counter‐clockwise
Rules for electron configurations
Hunds Rule• Orbitals in same sublevel are same energy
• Electrons fill orbitals of same energy so they maximize same spin
• Students don’t pair up in a seat until they have to
Putting the rules to use...• One electron for every proton
• Periodic table arranged by atomic number
• Typewriter method: start at H, read left to right, and stop at the element you’re configuring
HHeLiBeBCNOFNe
12345678910
Atomic # 1s 2s 2p
1s1
1s2
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
1s2 2s2 2p3
1s2 2s2 2p4
1s2 2s2 2p5
1s2 2s2 2p6
Orbital DiagramElectron
Configuration# of e‐ in orbitalNot
Exponent
Mg
S
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s2 3p4
↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ ↑Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2
↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓↑ ↑Se 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
4s is slightly lower energy than 3d, so
it fills first.Just follow the table from left to right.
I’ve seen the light!• Light made of electromagnetic waves
– Considered to be quanta of energy called photons
– Has properties of particles and waves
Amplitude
Crest
Trough
Wavelength (λ): distance between crests
Greek letter lambda
Light and the Universal Speed Limit
Frequency (ν): number of wave cycles to pass a given point per unit of time
SI unit is Hertz (Hz), or s‐1
Two are related by the formula:Since c is constant, λ and ν are inversely proportional
If one is big, the other is small
Greek letter nu
speed of light 3 x 108 m/s
A little light math…
• If you know either λ or ν, can solve for other
• Example: What is the wavelength of a wave with frequency equal to 5.10 x 1014 Hz?
Rearrange
The Electromagnetic Spectrum
I’ve seen the light!• Light made of electromagnetic waves
– Considered to be quanta of energy called photons
– Has properties of particles and waves
Amplitude
Crest
Trough
Wavelength (λ): distance between crests
Greek letter lambda
Light and the Universal Speed Limit
Frequency (ν): number of wave cycles to pass a given point per unit of time
SI unit is Hertz (Hz), or s‐1
Two are related by the formula:Since c is constant, λ and ν are inversely proportional
If one is big, the other is small
Greek letter nu
speed of light 3 x 108 m/s
A little light math…
• If you know either λ or ν, can solve for other
• Example: What is the wavelength of a wave with frequency equal to 5.10 x 1014 Hz?
Rearrange
The Electromagnetic Spectrum
The Electromagnetic Spectrum• Energy of light is related to frequency
Higher the frequency, more energy
• Visible light is small slice in the middle of spectrumRed is lowest ν (longest λ) that the human eye “sees”
So what does this have to do with electrons?
Ground state: electrons in lowest possible energy level
Excited state: atoms absorb energy and electrons move to higher energy levels– Once energy source is removed, electrons drop back down to ground state
– Emit quanta of energy in the form of…
light (sometimes visible)
Ouch! That’s hot!
Wow, I’m excited!
Oooo, pretty light!
Reading between the linesAtomic emission spectrum: pattern of discrete lines given off by electrons dropping to ground state– Energy levels are quantized
– Each line represents a frequency (energy) that is directly proportional to the energy lost by the electron
– No two elements haveexactly the samespectrum
• Each drop an electron makes relates to a specific frequency of energy
• Not all is in visible range, but always at discrete frequencies (not continuous)
Reading between the lines