Chapter 4.3 – Modern Atomic Theory

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