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Chapter 4.3 – Modern Atomic Theory

Chapter 4.3 – Modern Atomic Theory. Niels Bohr 1913 developed the planetary model of the atom differed from Rutherford’s model Rutherford said electrons could have any orbit Bohr’s model said electrons could only orbit the nucleus in certain paths or energy levels

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Chapter 4.3 – Modern Atomic Theory

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  1. Chapter 4.3 – Modern Atomic Theory Niels Bohr • 1913 developed the planetary model of the atom • differed from Rutherford’s model • Rutherford said electrons could have any orbit • Bohr’s model said electrons could only orbit the nucleus in certain paths or energy levels • the electrons cannot be between energy levels • to change energy levels the electrons have to gain or lose energy

  2. Chapter 4.3 – Modern Atomic Theory - 1925 Bohr’s model was no longer adequate - modern atomic model was then developed • said that we cannot find the exact location or speed of an electron in an atom • can find the probability of where the electron is orbital – a region in an atom where there is a high probability of finding an electron

  3. Chapter 4.3 – Modern Atomic Theory many orbitals make up the electron cloud – a cloud of electrons that surrounds the nucleus of an atom • there are a number of different energy levels that start at 1 and go up • the number of energy levels that are filled in an atom depends on the number of electrons in the atom • the electrons in the highest occupied energy level are the valence electrons • valence electrons determine an atoms chemical properties

  4. Chapter 4.3 – Modern Atomic Theory • each energy level has smaller levels called sublevels or orbitals • there are 4 kinds of orbitals: s, p, d, f • each orbital can hold 2 electrons • each orbital can have different orientations • an s orbital has the lowest energy, is shaped like a sphere, and there is only one on each energy level • a p orbital is shaped like a dumbbell and there are 3 of them - there are 5 d orbitals and 7 f orbitals and each have different shapes

  5. Chapter 4.3 – Modern Atomic Theory • the 1st energy level has only an s orbital and can hold 2 electrons • the 2nd energy level has an s and p orbitals and can hold 8 electrons • the 3rd energy level has s, p, and d sublevels and can hold 18 electrons • the 4th energy level has s, p, d, and f sublevels and can hold 32 electrons • electrons fill the lowest energy level first and then move to higher energy levels

  6. Chapter 4.3 – Modern Atomic Theory ground state – lowest energy of an electron excited state – energy level an electron moves to when it gains energy • electrons gain energy by absorbing particles of light or energy • because the electrons can only have certain energies they can only gain or lose certain amounts of energy or wavelengths of light • this is why neon lights and fireworks have certain colors

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