An atom is the basic building block of matter

Atom consists of a nucleus that is made of positively charged protons and neutrally charged neutrons

Electrons surround ("orbit") the nucleus

Simplest atom is the hydrogen atom: one proton in the nucleus and one electron

The ground state is the lowest energy state of an atom

An atom becomes ionized when an electron (or multiple electrons) acquires more than maximum energy and is no longer bound to the nucleus

The orbital energies of electrons are quantized

The modern view of an an atom has an electron cloud, not definite orbits

The number of protons in the nucleus defines the type of atom

Every atom has a unique spectrum -similar to fingerprints for humans

Excited state lasts about 10 ^-8s

If an electron absorbs an photon, then the electron absorbs energy and moves to a higher energy state

If an electron moves to a lower energy state, then the electron emits a photon= emission spectrum

The connection between atomic structure and the atomic spectra is the photon

Each photon has energy, E

E = hf (f= frequency of the photon)

h= Planck's constant = 6.63x10 ^-34 J s

The difference of energy between the electron orbit levels corresponds to a specific energy and a specific frequency of EM radiation

The energy needed to ionize the single electron in Hydrogen:

E=1.6 x 10^-19J= 13.6 eV

Electron transition

Vibrational modes

Rotational modes

Observed from solid objects (hot iron pokers, people, light bulbs)

Created by passing light through a prism or diffraction grating

Produced by low density hot gases

One can change the intensity of the individual lines, but not the wavelength (color)

Intensity depends on density, temperature

Each spectrum is a "fingerprint" of a particular element

First seen in high resolution spectrum of the Sun by William Wollaston in 1802

Josef von Fraunhofer catalogued over 600 dark lines

Dark lines occur at the same wavelength as emission lines

1MHz= 1 x 10⁶ Hz = 1 x 10⁶ /s (pg. A-2)

1 Solar Unit = mass of the Sun= 1.99 x 10³⁰ kg= M_M

Continuous -- band of constant emission

Emission-- narrow lines of color at specific wavelengths

Absorption-- Dark lines in the midst of a continuous spectrum

A luminous solid or liquid, or a sufficiently dense gas, emits light at all wavelengths and produces a Continuous Spectrum

A low density hot gas emits an Emission Line Spectrum where the lines occur at specific wavelengths that are characteristic of the chemical composition of the gas

A cool thin gas absorbs specific wavelengths from a continuous spectrum , leaving dark lines at specific places superimposed on the continuous spectrum. This produces an Absorption Line Spectrum.

Atoms moving randomly produce broadened lines. The hotter the gas, the greater the broadening.

Rotational Broadening: The bulk motion of the atoms, such as a star, which is a ball of gas, produces a net broadening.