Lesson 16 Modern View of the Atom  Learning Targets: I can explain the properties of waves I can calculate the wavelength of an electromagnetic wave. I can understand the particle nature of light and calculate the energy of a photon. I can explain the difference between excited state and ground state electrons. I can define and explain an orbital. I can explain the basic principles of the electron cloud model of the atom.

Wave Nature of Light A.Electromagnetic Radiation-form of energy that exhibits wavelike behavior as it travels through space. i. Ex. Visible light, microwaves, x-rays radio, and television waves. Wavelength-symbol-______shortest distance between equivalent points on a continuous wave. Measured from crest to crest or trough to trough Units-meters, centimeters, nanometers Frequency-symbol-_____is the number of waves that pass a given point per second. One hertz is the SI unit of frequency, equals one wave per second Amplitude-is the wave’s height from the origin to a crest, or from the origin to a trough.

All electromagnetic waves, including visible light travel at a speed of light (c ) which equals 3.00 * 108 meters/second Electromagnetic spectrum- encompasses all forms of electromagnetic radiation, with the only differences in the types of radiation being their frequencies and wavelengths

Calculating Wavelength of an EM Wave Sample 1: Microwaves are used to transmit information. What is the wavelength of a microwave having a frequency of 3.44 * 10 9 Hz?

Particle Nature of Light The Quantum Concept The wave model could not explain the emission of different wavelengths of light at different temperatures. Max Plank- matter can gain or lose energy only in small, specific amounts called quanta. Quantum- the minimum amount of energy that can be gained or lost by an atom. The energy of a quantum is related to the frequency of the emitted radiation by the equation: Equantum=hv E=energy H=Planck’s constant V=frequency Planck’s constant=6.626 * 10-34J * S  For a given frequency, v, matter can emit or absorb energy only in whole number multiples of hv, 1hv, 2hv, 3hv, 4hv ….

 The photoelectric effect-electrons called photoelectrons are emitted from a metal’s surface when light of a certain frequency shines on the surface. In order to explain the photoelectric effect, Albert Einstein proposed electromagnetic radiation has both wavelike and particle like natures. Photons- particle of electromagnetic radiation with no mass that carries a quantum of energy. Einstein calculated a photon’s energy depends on it’s frequency: Ephoton=hv

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

a. Dalton – Marbles – Solid, indivisible spheres. 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.