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.

How do rainbows have color?

I. I. The modern view of the atom a. 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.

The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element. Each element’s atomic emission spectrum is unique.

v. White light produces the entire visible spectrum.

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 Uncertainty Principle. 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:

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.Rutherford – Solar System – Small, positively charged nucleus, with negatively charged electrons in well defined orbital paths around it. d.Bohr – Step-Ladder model – Electrons are quantized, or locked into specific energy levels around the nucleus. 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 TERMS to 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 atom 4.Leptons: light particles: e-, positrons, muons, taus, & neutrinos 5.Hadrons: heavy particles: protons & neutrons 6.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 hadrons 10.Gluons: theoretical particle; are exchanged and hold together quarks. 11.Radiation: particles emitted by spontaneous radioactive decay. 12.Alpha particle: helium nucleus; 2p, 2n 13.Beta particle: is an electron or a positron 14.Gamma rays: x-rays, energy with high frequency and short wavelength.