2. Electron Energy Levels Not all electrons in an atom have the same energy They exist in discreet energy levels These levels are arranged in shells (n = 1, n = 2…) Electrons closer to the nucleus have lower energy (stabilized by positively charged nucleus) Maximum number of electrons in a shell = 2n 2, where n = the shell # Electrons fill shells from lowest E up

3. Electron Shells

4. Electromagnetic Radiation Electromagnetic radiation consists of photons (particles) that travel as waves Examples: light, x-rays and radio waves Distance between peaks is called the wavelength Longer wavelength = lower energy Electrons can jump to a higher energy level by absorbing energy (light, heat…) When they drop back down to their original E, sometimes visible light is emitted (neon lights)

5. Electromagnetic Spectrum

6. Subshells Electrons within each shell are not all the same E They are arranged into subshells (s, p, d, f) The E order of the subshells goes s < p < d < f Number of subshells = shell number n = 1 has only s, n = 2 has s and p, etc. As n increases, main E levels are closer, so there is some overlap (4s subshell is lower E than 3d)

7. Orbitals Each subshell is made up of orbitals An orbital is a region of space in which electrons of that E level are most likely to be found The s subshell has only one orbital (spherical) The p subshell has three orbitals (dumbell shaped) Each orbital can contain 0, 1 or 2 electrons So s has a max of 2 electrons and p has a max of 6 electrons (2 for each orbital)

10. Electron Configurations The electron configuration shows how the electrons are arranged in the subshells of an atom Written as the shell number and subshell symbol, with number of electrons in the subshell as superscript Examples: Li = 1s 2 2s 1 S = 1s 2 2s 2 2p 6 3s 2 3p 4 Use periodic table to get electron configuration (check that superscripts add up total number of electrons = atomic number)