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 = 2n2, where n = the shell #

• Electrons fill shells from lowest E up

Electron Shells

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)

Electromagnetic Spectrum

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)

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)

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 = 1s22s1 S = 1s22s22p63s23p4

• Use periodic table to get electron configuration

• (check that superscripts add up total number of electrons = atomic number)