1. Modern Atomic Theory 4.3

2. Bohr’s model A. Concentrated on placement of electrons around the nucleus B. Looks like planets revolving around the sun

3. C. Electrons move at constant speed in fixed orbits around nucleus D. Electrons can gain or lose energy by moving to different energy levels (also called shells) E. When electrons move to a lower energy level, they emit light or give off heat

5. Electron Cloud Model A. Electrons don’t really move in a predictable way, like the planets in the solar system B. Electron cloud model shows the most likely location of electrons 1. Hard to predict exactly where they are

6. Atomic Orbitals A. Orbital – space around the nucleus where an electron is likely to be found 1. electron cloud represents all the orbitals in an atom B. Each energy level has different number of orbitals

7. Energy Level Number of Orbitals Number of Orbitals Max. # of Electrons 1 (K) 12 2 (L) 48 3 (M) 918

8. Electron Configuration A. Electron configuration – the arrangement of electrons in the orbitals of an atom B. The most stable electron configuration is one in which the electrons are in the lowest possible orbital – this is the ground state

9. C. When electrons move away from the ground state to a higher orbit, they become “excited” and the atom is less stable D. When the electrons move back to the ground state, they give off light Example: neon, argon, xenon