Emission Spectra and Flame Tests

The Big Questions

What is light? How is light emitted? What do electrons have to do with light? What are emission spectra? How do flame tests help identify metals?

The Electromagnetic Spectrum

All light is part of the EM spectrum. Most is invisible:

gamma, X-rays, UV, IR, microwaves, radio waves Visible light: wavelength (w.l.) from 400 to 700

nm.

The EM Spectrum

EM Radiation

Light is a carrier or quantum of energy. It is emitted by vibrating charges (like

electrons). Light can transfer energy to electrons.

Heat can also excite electrons.

Energy of Electrons

Ground State

The lowest possible energy of the electron

Excited State Electron that absorbs energy

and has moved to a higher energy level

Adding Energy

Electrons move from a lower energy level to a higher energy level

This occurs when the electron absorbs light

Light and Electrons

Ground state (G.S.) electron

Excited state (E.S.) electronLight

Losing Energy

Electrons give off energy (light) as they move from a higher energy level to a lower energy level

Energy of light corresponds to the energy gap between ground state and excite state

Sometime the light is visible

Light and Electrons

Ground state (G.S.) electron

Excited state (E.S.) electron

Lyman Series

Lines at the ultraviolet end of the hydrogen spectrum Electrons move from a higher energy level to

n=1

Balmer Series

Lines in the visible spectrum Electrons move from a higher energy level to

n=2

Paschen Series

Lines at the infrared end of the hydrogen spectrum Electrons move from a higher energy level to

n=3

Emission Spectrum

Emission spectrum – colors of light given off by an element when it is excited (usu. by heat). Every element has an unique emission

spectrum.

Emission Spectra

Hydrogen

Helium

Carbon

Flame Tests

Flame test – used to ID some metals in compounds. Each metal gives a

flame a characteristic color.

Can identify metals based on flame colors.