AS.C5_chemistry notes
- 2. Ernest, we have a problem... • Rutherford’s model didn’t explain chemical 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)
- 3. 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
- 4. 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
- 5. Sublevels and orbitals s sublevel – one spherical orbital – one in every energy level p sublevel – three dumbell‐shaped orbitals – in all energy levels ≥ 2
- 6. 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
- 8. 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
- 9. Where do electrons live? Electron’s address • Energy level • Sublevel • Orbital • Spin Your address • State • Town • Street • House Need a system for electron addresses...
- 10. 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
- 11. 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
- 12. 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
- 13. 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
- 14. 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
- 15. H He Li Be B C N O F Ne 1 2 3 4 5 6 7 8 9 10 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 Diagram Electron Configuration # of e‐ in orbital Not Exponent
- 16. 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.
- 17. 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
- 19. 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
- 21. 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
- 23. 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
- 25. The Electromagnetic Spectrum • Energy of light is related to frequency Higher the frequency, more energy • Visible light is small slice in the middle of spectrum Red is lowest ν (longest λ) that the human eye “sees”
- 27. Reading between the lines Atomic 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 have exactly the same spectrum