Chem Activity Sheet

DE LA SALLE HEALTH SCIENCES INSTITUTE

CITY OF DASMARIÑAS

EXPERIMENT NO. 5

FLAME COLOR OF METALS

OBJECTIVES:

1. To observe the flame colors emitted by excited metal atoms

2. To explain the flame colors in terms of electronic transitions in atoms

INTRODUCTION:

The current model of an atom includes a nucleus, consisting of protons and neutrons, surrounded by electrons. According to experiments on atomic absorption and emission spectra, the energy of electrons is quantized. It means that each electron in an atom has a definite energy.

When an atom absorbs energy from a flame or electric discharge, it absorbs just enough energy to excite its electrons from a lower energy state to a higher energy state. Alternatively, when the atom from an excited state returns to a lower energy state, it emits the energy previously absorbed in the form of light.

The energy of emitted or absorbed light is equal to the energy difference between the two energy states, and is inversely proportional to its wavelength. The following equations express the mathematical relationship between energy, wavelength, and frequency of light.

Equation (1) E=hc/ƛ

Equation (2) E=hv

where E is the energy of light

c is the speed of light (3.00 x 108 m/s)

h is Planck’s constant (6.63 x 10-34 J-s)

v is the frequency of light

ƛ is the wavelength

Since many electronic energy states exist for a given atom, a large number of excited states are available. Therefore, when light is emitted by a large collection of atoms, a variety of energies and wavelengths are released as the electrons return to their lowest energy state. When this light passes through a prism, a line spectrum is produced. Each line corresponds to a particular energy and wavelength.

Each element exhibits its own characteristics line spectrum because the spacing of electronic energy states in atoms of different elements are different. Thus, excited sodium atom produces yellow color...