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12.2 Learning Goals

Learn about the spectra of elements, the Bohr atom model, and the behavior of electrons in atoms. Discover how energy levels and orbitals contribute to the unique properties of each element's spectrum.

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12.2 Learning Goals

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  1. 12.2 Learning Goals • Compare spectra of elements. • Explain the Bohr atom model. • Apply principles of quantum theory to explain the behavior of electrons in atoms.

  2. 12.2 Electrons in the atom • Each different element has its own characteristic pattern of colors called a spectrum. • The colors of clothes, paint, and everything else around you come from this property of elements to emit or absorb light of only certain colors.

  3. 12.2 Electrons in atoms • Each individual color in a spectrum is called a spectral line because each color appears as a line in a spectroscope. • A spectroscope is a device that spreads light into its different colors.

  4. 12.2 Bohr model of the atom • Danish physicist Neils Bohr proposed the concept of energy levels to explain the spectrum of hydrogen. • When an electron moves from a higher energy level to a lower one, the atom gives up the energy difference between the two levels. • The energy comes out as different colors of light.

  5. 12.2 Electrons and energy levels • In the current model of the atom, we think of the electrons as moving around the nucleus in an area called an electron cloud. • The energy levels occur because electrons in the cloud are at different average distances from the nucleus. • Energy levels are sometimes referred to as “shells”.

  6. 12.2 Rules for energy levels/shells Inside an atom, electrons always obey these rules: • The energy of an electron must match one of the energy levels in the atom. • Each energy level can hold only a certain number of electrons, and no more. • As electrons are added to an atom, they settle into the lowest unfilled energy level.

  7. 12.2 Energy levels/shells • In the Bohr model of the atom, the first energy level can accept up to two electrons. • The second and third energy levels hold up to eight electrons each. • The fourth and fifth 9 (and 3rd) energy levels hold 18 electrons. BUT THE LAST 10 ARE ONLY ADDED AFTER 2 ARE ADDED TO THE NEXT HIGHER LEVEL FIRST!

  8. 12.2 Electrons and energy levels • The first energy level can accept up to two electrons. • The second energy levels hold up to eight electrons.

  9. Orbitals • Electrons are 'said' to occupy orbitals in an atom.  The term orbital is somewhat 'erroneous' as electrons do not 'orbit' around a nucleus. • Describes a region of high probability in 3D space, about a nucleus, where an electron may be found. • There energy levels are made of “subshells”, each are denoted by a letter (s, p, d, and f) composed of 1 or more orbitals. • Orbitals hold up to 2 electrons each. s-subshells – found in all energy levels p subshells – in all but 1st energy level d-subshells – in levels 3 thru 6 only f-subshells - in levels 4 and 5 only Wiki!

  10. s-subshells have 1 s orbital ; holds 2 total electrons • p-subshells have 3 p orbitals: 3 pair of 2 = 6 total • d-subshells have 5 d orbitals: 5 pair of 2 = 10 total • f-subshells have 7 f orbitals: 7 pair of 2 =14 total

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