Wednesday, Oct. 31 st : “A” Day (1:05 dismissal) Thursday, Nov. 1 st : “B” Day  Homework questions?  Sec. 3.2 Quiz: “Structure of Atoms”  Begin Section 3.3: “Electron Configuration”  Atomic models Rutherford, Bohr, quantum, orbitals  Electrons and light Electromagnetic spectrum, line-emission spectrum, ground state, excited state  Movie: “Bohr’s Model of the Atom”  Homework: NONE! We will finish section 3.3 next time

Homework Questions  Sec. 3.2 review, pg. 89: #1-8  “Writing Nuclear Symbols” Worksheet

Quiz Section 3.2: “Structure of Atoms”  You can use your notes, your book and a partner of your choice to complete this quiz…

Rutherford’s Model Proposed Electron Orbits  Rutherford’s findings led to the replacement of Thomson’s plum pudding model with a nuclear model of the atom.  Rutherford suggested that electrons are like planets orbiting the sun and revolve around the nucleus in circular or elliptical orbits.  Because Rutherford’s model could not explain why electrons did not crash into the nucleus, it was replaced only two years later by a model developed by Niels Bohr.

Bohr’s Model Confines Electrons to Energy Levels  In Bohr’s model, electrons can only be certain distances from the nucleus. Each distance corresponds to a certain quantity of energy that an electron can have. An electron that is as close to the nucleus as it can be is in its lowest energy level. The farther an electron is from the nucleus, the higher the energy level that the electron occupies.  The difference in energy between two energy levels is known as a quantum of energy.

Think of Bohr’s energy levels as rungs on a ladder, with Earth being the nucleus… You can only be on certain energy levels, or rungs, of the ladder but you can’t be in between them. You are at your lowest energy level at the bottom of the ladder. (closest to Earth) You are at your highest energy level at the top rung of the ladder. An electron can only be in certain, definite energy levels, not in between them.

Atomic Models Rutherford  Electrons orbit the nucleus just as planets orbit the sun Bohr  Electrons travel around the nucleus in specific energy levels

Electrons Act Like Both Particles and Waves  In 1924, Louis de Broglie suggested that electrons behaved like waves that are confined to the space around a nucleus.  As waves, electrons could have only certain frequencies which correspond to the specific energy levels where electrons are found.

Quantum Model (electron cloud model) **the present-day model of the atom**  In this model, electrons are located in orbitals.  Orbital: a region in an atom where there is a high probability of finding electrons.  Orbitals are sometimes called electron clouds because they do not have sharp boundaries. Because electrons can be in other places, the orbital has a fuzzy boundary like a cloud.  A single orbital can hold a maximum of 2 electrons.

 Electromagnetic Spectrum: all of the frequencies or wavelengths of electromagnetic radiation.  Our eyes are sensitive to only a small portion of the electromagnetic spectrum.

Hydrogen’s Line-Emission Spectrum

Light Emission  When a high-voltage current is passed through a tube of hydrogen gas at low pressure, lavender- colored light is seen. When this light passes through a prism, you can see that the light is made of only a few colors. This spectrum of a few colors is called a line-emission spectrum.  Experiments with other gaseous elements show that each element has a unique line-emission spectrum that is made of a different pattern of colors.  It’s like a “fingerprint” for each element.

Light Emission  In 1913, Bohr showed that hydrogen’s line-emission spectrum could be explained by assuming that the hydrogen atom’s electron can be in any one of a number of distinct energy levels.  An electron can move from a low energy level to a higher energy level by absorbing energy.  Electrons at a higher energy level are unstable and can move to a lower energy level by releasing energy. This energy is released as light that has a specific wavelength.  Each move from a particular energy level to a lower energy level will release light of a different wavelength.

Light Provides Information About Electrons  Ground state: the lowest energy state of a quantized system. (bottom rung of ladder)  If an electron gains energy, it moves to an excited state.  Excited state: a state in which an atom has more energy than it does at its ground state.

Light Provides Information About Electrons  An electron in an excited state will release a specific quantity of energy as it quickly “falls” back to its ground state and it emits a characteristic wavelength of light.  This energy is emitted as certain wavelengths of light, which give each element a unique, line-emission spectrum.

Movie: “Bohr’s Model of the Atom”  I know we covered a LOT of background material today to get ready to write electron configurations next time….  You DO NOT have to take notes on the movie…  Remember to update your KWL as we go through this chapter…

Happy Halloween!!