4-2 The Quantum Model of the Atom

1. 4-2The Quantum Model of the Atom

2. Beaker Breaker • Who was the scientist that thought electrons can circle the nucleus at set distances…only in allowed paths, or orbits? (solar system model) • Now light can also be thought of as a stream of particles called_________ • ________________spectrum:all wavelengths are present

3. De Broglie, 1924 • If light could behave as both a wave and a particle, then could an electron (a particle) also behave as both a particle and a wave ????????????? • He said “YES” because…. • Since electrons could only exist at specific energies, and E can be equated to frequency(E = hν), they have wave properties • And electrons can be “focused” like light (electron microscopes) • particle nature of electrons had already been confirmed (cathode rays, oil drop exper, etc.)

4. Diffraction/Interference • Diffraction refers to the bending of a wave as it passes by the edge of an object • Diffraction experiments showed that electron beams, like waves, can interfere with each other. • Interference occurs when waves overlap. • Overlapping results in a reduction of energy in some areas and an increase of energy in others.

5. Electrons have a dual wave-particle nature

6. Heisenberg Uncertainty Principle • It is impossible to determine simultaneously both the position and velocity of an electron or any other particle

7. Schrodinger Wave Equation, 1926 • If electrons have wave properties, then wave equations can be applied to electrons (and other small particles) • Laid foundation for quantum theory: describes mathematically the wave properties of electrons and other very small particles • Gives the probability of finding an electron at a given place in time around the nucleus

8. Quantum Theory (con’t) • Electrons do NOT travel around the nucleus like planets around the sun • Electrons exist in certain regions called orbitals: a 3-D region around the nucleus that indicates the probable location of an electron

9. Quantum Numbers • Specify the properties of atomic orbitals and the properties of electrons in orbitals • There are FOUR quantum numbers….the first three of which come from solutions to Schrodinger’s wave equation

10. What 2 things does the first quantum # tell us about an atom? • # energy levels in an atom that the electrons can occupy • size of the atom

11. Principal Quantum Number, n • Indicates the main energy level (or shell) occupied by the electron • n = 1, 2, 3 etc. • The ↑n value, the farther the electron is from nucleus∴ prin quant # also gives size info • Total # electrons on a level = 2n2 • Ex: n =2 total electrons = 2(2)2 = 8 • Total # orbitals on a level = n2 since an orbital can hold two electrons (2n2/2= n2)

12. Angular Momentum Quantum Number, l • Also known as “second quantum number” • Also known as “azimuthal quantum number” • Most energy levels (all but n=1) have orbitals of different shapes, called sublevels • Describes the shape of the orbital • # orbital shapes possible is equal to the “n” value • If n=3, then there can be 3 orbital shapes • The values of l = 0, 1, 2,……. (n-1) • If n=3, then l can be “0”, or “1”, or “2”

13. 1s sublevel • 1st: probability map (where electrons spend 90% of their time) • 2nd: surface map ( encloses an area within which the electron spends 90% of its time…10% somewhere outside this surface. Electrons don’t travel on the surface!

14. s orbital

15. 2p-sublevel • 1st: probability map (where electrons spend 90% of their time) • 2nd: surface map ( encloses an area within which the electron spends 90% of its time…10% somewhere outside this surface. Electrons don’t travel on the surface!

16. Angular Momentum Quantum Number, l(con’t) • An orbital LETTER is used to designate each shape:

23. What do the first two quantum numbers tell you? • 1st (principal): • Size of the orbital • 2nd (angular momentum): • Shape of the orbital

24. Magnetic Quantum Number, ml also known as the 3rd quantum number indicates the orientation of an orbital around the nucleus = (2 l + 1)

25. s orbital

26. p orbitals

27. Three 2p orbitals • 1st of each: probability map (where electrons spend 90% of their time) • 2nd of each: surface map ( encloses an area within which the electron spends 90% of its time…10% somewhere outside this surface. Electrons don’t travel on the surface!

28. “s” “p” “d”

29. d orbitals

30. f-orbitals 

31. Magnetic Quantum Number, m (con’t) • Sum of all orbitals in a sublevel (or E level) is a spherical cloud!

32. Spin quantum number • Describes the spin of the electron • Could be either clockwise ( + ½) or counterclockwise (- ½ ) • Each orbital can hold a maximum of two electrons, a pair, spinning in opposite directions

33. Pauli Exclusion Principle • No 2 electrons in an atom have the same set of four quantum numbers

34. SuperPremium Dog Food