What Is Light? Light is formed when electrons drop from the excited state to the ground state. The lines on a bright-line spectrum come from specific energy level drops and are unique to each element. Ex. Emission and Absorption Spectra ( line spectra)

EXAMPLE SPECTRUM This is the bright-line spectrum of hydrogen. The top numbers represent the energy level transition change that produces the light with that color and the bottom number is the wavelength of the light (in nanometers, or 10-9 m). No other element has the same bright-line spectrum as hydrogen, so these spectra can be used to identify elements or mixtures of elements.

Development of the Atomic Model Thompson Model Rutherford Gold Foil Experiment and Model Bohr Model Quantum-Mechanical Model

Thompson Model The atom is a positively charged diffuse mass with negatively charged electrons stuck in it.

Rutherford Model The atom is made of a small, dense, positively charged nucleus with electrons at a distance, the vast majority of the volume of the atom is empty space. Alpha particles shot at a thin sheet of gold foil: most go through (empty space). Some deflect or bounce off (small + charged nucleus).

Bohr Model Electrons orbit around the nucleus in energy levels (shells). Atomic bright-line spectra was the clue.

Quantum-Mechanical Model Electron energy levels are wave functions. Electrons are found in orbitals, regions of space where an electron is most likely to be found. You can’t know both where the electron is and where it is going at the same time. Electrons buzz around the nucleus like gnats buzzing around your head.

Orbital Quantum Numbers Symbol Name Description Meaning Equations n Principle Q.N. Energy level (i.e. Bohr’s theory) Shell number n = 1, 2, 3, 4, 5, 6, 7 n = 1, 2, 3, … l Angular Momentum Q.N. General probability plot (“shape” of the orbitals) Subshell number l = 0, 1, 2, 3   l = 0 means “s” l = 1 means “p” l = 2 means “d” l = 3 means “f” l = 0, 1, 2, …, n – 1 Ex: If n = 1, l can only be 0; if n = 2, l can be 0 or 1.

Symbol Name Description Meaning Equations ml ms Magnetic Q.N. 3-D orientation of the orbital s has 1 p has 3 d has 5 f has 7 ml = -l, -l +1, …, 0, l, …, +l   There are (2l + 1) values.   ms Spin Q.N. Spin of the electron Parallel or antiparallel to field ms = +½ or -½ * s, p, d, and f come from the words sharp, principal, diffuse, and fundamental.

Permissible Quantum Numbers (4, 1, 2, +½) (5, 2, 0, 0) (2, 2, 1, +½) Not permissible; if l = 1, ml = 1, 0, or –1 (p orbitals only have 3 subshells) Not permissible; ms = +½ or –½ Not permissible; if n = 2, l = 0 or 1 (there is no 2d orbital)