End Show Slide 1 of 20 Ch. 5: Models of the Atom What you need to know: Chapter 5 Timeline pp (theory and people) Definitions: quantum mechanical model, atomic orbitals, speed of light, electromagnetic radiation, atomic emission spectrum (ROYGBIV), ground state, photon Bohr model Electron configurations

End Show Slide 2 of 20 The Development of Atomic Models The timeline shoes the development of atomic models from 1803 to This timeline needs to be in your notes!

End Show Slide 3 of 20 The Development of Atomic Models The timeline shows the development of atomic models from 1913 to

End Show Slide 4 of The Bohr Model Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus Each orbit has a particular energy level; electrons must gain or lose energy to move from one energy level to the next A quantum of energy is the amount of energy required to move an electron from one energy level to another energy level

End Show Slide 5 of Quantum mechanical model Mathematically determined by Erwin Schrodinger determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron. –Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found. (s, p, and d orbitals) (Bohr used orbits; Schrodinger used orbitals)

End Show Slide 6 of 20 Atomic Orbitals Different atomic orbitals are denoted by letters. The s orbitals are spherical, and p orbitals are dumbbell-shaped. 5.1

End Show Slide 7 of 20 Atomic Orbitals The numbers and kinds of atomic orbitals depend on the energy sublevel. 5.1

End Show Slide 8 of 20 Atomic Orbitals The number of electrons allowed in each of the first four energy levels are shown here. 5.1

End Show © Copyright Pearson Prentice Hall Slide 9 of 20 Electron Arrangement in Atoms If this rock were to tumble over, it would end up at a lower height. It would have less energy than before, but its position would be more stable. You will learn that energy and stability play an important role in determining how electrons are configured in an atom. 5.2

End Show © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Slide 10 of 20 Electron Configurations What are the three rules for writing the electron configurations of elements? 5.2

End Show Slide 11 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configurations The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations. Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms. 5.2

End Show Slide 12 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configurations Aufbau Principle According to the aufbau principle, electrons occupy the orbitals of lowest energy first. In the aufbau diagram below, each box represents an atomic orbital. 5.2

End Show Slide 13 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configurations Pauli Exclusion Principle According to the Pauli exclusion principle, an atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins; that is, the electron spins must be paired. 5.2

End Show Slide 14 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configurations Hund’s Rule Hund’s rule states that electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible. 5.2

End Show Slide 15 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configurations Orbital Filling Diagram 5.2

End Show Slide 16 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Electron Configuration and Orbital Filling Practice 1.Write the electron configuration and orbital filling for a. Li b. Mg c. Si a.Li: atomic number 3 1s 2 2s 1 b. Mg: atomic number 12 1s 2 2s 2 2p 6 3s 2 c.Si: atomic number 14 1s 2 2s 2 2p 6 3s 2 3p 2

End Show © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Slide 17 of 20 Exceptional Electron Configurations Why do actual electron configurations for some elements differ from those assigned using the aufbau principle? 5.2

End Show © Copyright Pearson Prentice Hall Slide 18 of 20 Electron Arrangement in Atoms > Exceptional Electron Configurations Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations. 5.2

End Show Slide 19 of 20 © Copyright Pearson Prentice Hall Electron Arrangement in Atoms > Exceptional Electron Configurations Exceptions to the aufbau principle are due to subtle electron-electron interactions in orbitals with very similar energies. Copper has an electron configuration that is an exception to the aufbau principle. 5.2

© Copyright Pearson Prentice Hall Slide 20 of 20 End Show Light According to the wave model, light consists of electromagnetic waves. Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays. All electromagnetic waves travel in a vacuum at a speed of  10 8 m/s. 5.3

© Copyright Pearson Prentice Hall Slide 21 of 20 End Show Light Sunlight consists of light with a continuous range of wavelengths and frequencies. When sunlight passes through a prism, the different frequencies separate into a spectrum of colors. In the visible spectrum, red light has the longest wavelength and the lowest frequency. ROYGBIV (red, orange, yellow, green, blue, indigo, violet) 5.3

© Copyright Pearson Prentice Hall Slide 22 of 20 End Show Light The electromagnetic spectrum consists of radiation over a broad band of wavelengths. 5.3

© Copyright Pearson Prentice Hall Slide 23 of 20 End Show Atomic Spectra What causes atomic emission spectra? 5.3

© Copyright Pearson Prentice Hall Slide 24 of 20 End Show Atomic Spectra When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels. 5.3

© Copyright Pearson Prentice Hall Slide 25 of 20 End Show 5.3 Atomic Spectra a.A prism separates light into the colors it contains. When white light passes through a prism, it produces a rainbow of colors.

© Copyright Pearson Prentice Hall Slide 26 of 20 End Show 5.3 Atomic Spectra a.When light from a helium lamp passes through a prism, discrete lines are produced.

© Copyright Pearson Prentice Hall Slide 27 of 20 End Show 5.3 Atomic Spectra a.The frequencies of light emitted by an element separate into discrete lines to give the atomic emission spectrum of the element. Mercury Nitrogen

© Copyright Pearson Prentice Hall Slide 28 of 20 End Show 5.3 An Explanation of Atomic Spectra An Explanation of Atomic Spectra How are the frequencies of light an atom emits related to changes of electron energies?

© Copyright Pearson Prentice Hall Slide 29 of 20 End Show 5.3 An Explanation of Atomic Spectra a.In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies. When the electron has its lowest possible energy, the atom is in its ground state. Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state. A quantum of energy in the form of light (photon) is emitted when the electron drops back to a lower energy level.

© Copyright Pearson Prentice Hall Slide 30 of 20 End Show 5.3 An Explanation of Atomic Spectra The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.

© Copyright Pearson Prentice Hall Slide 31 of 20 End Show 5.3 Quantum Mechanics Light was found to have properties similar to…. a.In 1905, Albert Einstein successfully explained experimental data by proposing that light could be described as quanta of energy. The quanta behave as if they were particles. Light quanta are called photons. b.In 1924, De Broglie developed an equation that predicts that all moving objects have wavelike behavior.