Lesson 16 Modern View of the Atom

Objectives:

1. The student will explain the difference between excited state and ground state electrons.

2. The students will define and explain an orbital

3. The student will explain the basic principles of the electron cloud model of the atom.

I.               I.     The modern view of the atoma.      Electrons can be described as particles or waves

This is called the wave/particle duality of nature

                        i.      When all the electrons are in their lowest energy levels for a substance, it is said to be in the ground state.

                        ii.      When electrons are boosted to higher energy levels, they are said to be in an excited state.

                       iii.      When electrons move from an excited state to the ground state, the substance emits the energy as light

                      iv.      This light is known as a bright-line emission spectrum.

v. White light produces the entire visible spectrum.

Atomic Emmissions

Virtual Labs

Disc 1

We will demonstrate the bright line emission spectrum through what is

called the Flame Test in our laboratory

virtual lab 1 flame test

b.       Quantum theory provides a modern picture of the atom.   i.      Quantum theory is the description of the properties of atoms using wave properties

              ii.      This theory is based on the idea that we can only predict the probability of finding an electron in a particular position

              iii.      When these regions where the electrons are most likely to be found are plotted on a graph, they form orbitals. – drawn as a solid area, these show where an electron can be found 90% of

the time.

              iv.      This is known as the electron cloud model.

              v.      Both the position and the velocity of a particular electron cannot be known at the same time: Heisenberg’s UncertaintyPrinciple.

              vi.      This shows that there is a limit to what we can know about an atom.

                                                               viii.      The following are diagrams of several of the atomic electron orbital shapes:

The exotic, complex f orbital shapes are rarely shown in textbooks. General (and organic) chemistry traditionally focuses on the lighter elements, but the f orbitals aren't occupied in the ground state until element 58 (cerium). Even for elements beyond cerium, the f orbitals are deeply buried beneath the valence shell and they rarely play an important role in chemical change or bonding. However, the orbital shapes can be useful in interpreting spectra and in understanding the structure of some complexes that involve the rare earth elements. So here they are, if you need them.

The 4fy3

- 3x2

y orbital corresponds to n=4, l=3, and m =-3. Six lobes point to the

corners of a regular hexagon in the xy plane, with one pair of lobes along the x-axis. Three nodal planes pass between the lobes and intersect at the z axis.

The 4fxyz orbital corresponds to n=4, l=3, and m =-2. Eight lobes point to the

corners of a cube, with four lobes above and four lobes below the xy plane. The x and y axes pass through the centers of four of the cube's faces (between the lobes). The three nodal planes are defined by the x, y, and z axes.

The 4f5yz2

- yr2 orbital corresponds to n=4, l=3, and m =-1. Six lobes point to the

corners of a regular hexagon in the yz plane, with one pair of lobes along the x-axis. The three nodal planes pass between the lobes and intersect at the y axis.

The 4fz3

- 3zr2 orbital corresponds to n=4, l =3, and m =0. Two lobes point along

the z-axis, with two bowl-shaped rings above and below the xy plane. The nodal surfaces are the xy plane and a conical surface passing through the nucleus and between the rings and the lobes.

The 4f5xz2

- xr2 corresponds to n=4, l=3, and m =+1. Six lobes point to the

corners of a regular hexagon in the xz plane, with one pair of lobes along the y-axis. The three nodal planes pass between the lobes and intersect at the x axis.

The 4fzx2

- zy2 orbital corresponds to n=4, l =3, and m =+2. It has the same

shape as the 4fxyz orbital, but the corners of the cube are in the planes defined

by the x, y, and z axes and the three nodal planes cut between the lobes and intersect along the z axis.

The 4fx3

- 3xy2 orbital corresponds to n=4, l =3, and m =+3. It is identical to the

orbital with m_ =-3 except that a lobe lies along the y axis instead of along the x axis.

c. The atom is a scientific model                                               i.      Many models have been developed, such as Dalton’s (indivisible spheres), Thompson’s (plum

pudding), Ruthorford’s (idea of the nucleus and planetary orbits), and Bohr’s (quantitized electrons)

                                                              ii.      Models are revised as new discoveries are made.

                                                iii.      The current model can be revised if new

experimental data suggests there are mistakes in the current theory

II.                Review

a.      Dalton – Marbles – Solid, indivisible spheres.

b. Thompson – Plum Pudding – Positively charged material, with negatively charged electrons embedded in it.

c.      c. Rutherford – Solar System – Small, positively charged nucleus, with negatively charged electrons in well defined orbital paths around it.

d.     d. Bohr – Step-Ladder model – Electrons are quantized, or locked into specific energy levels around the nucleus.

e.  e. Many – Electron Cloud model – Electrons orbit the nucleus in cloud shaped orbitals, determined by the probability of finding an electron in a specific area.

ATOMIC TERMSto add to your lecture notes

1. Nuclear force: force holding nucleons together in the nucleus.

2. Nucleons: particles in the nucleus (p+ , n)3. Subatomic particles: particles smaller than an atom4. Leptons: light particles: e- , positrons, muons, taus,

& neutrinos5. Hadrons: heavy particles: protons & neutrons6. Antiparticle: particle identical to another in all

respects except opposite charge and magnetic moment.

7. Neutrino: neutral particle classed as a lepton.8. Quark: theoretical particle; constituents of

hadrons. Elementary particles.9. Baryons & Mesons: classes of hadrons10. Gluons: theoretical particle; are exchanged and

hold together quarks.11. Radiation: particles emitted by spontaneous

radioactive decay.12. Alpha particle: helium nucleus; 2p, 2n13. Beta particle: is an electron or a positron14. Gamma rays: x-rays, energy with high

frequency and short wavelength.