Chemistry

# Electromagnetic Wave Theory

## Wave Nature of Electromagnetic Radiation

• Electromagnetic wave theory states that is emitted from a source when it is heated this is emitted continuously in the form of radiations.
• These radiations associated with an electric and magnetic field which are perpendicular to one another.

### Limitations of Electromagnetic Wave Theory

Electromagnetic wave theory was unable to explain:

• Photoelectric effect

An black body is a perfect absorber and emitter of radiations.

#### Photoelectric Effect

• Phenomena of ejection of an electron from a metal surface when the light of suitable frequency falls on the metal surface.
• The minimum frequency which is required to eject an electron is called threshold frequency.
• The kinetic of the emitted electron is directly proportional to the frequency but independent of intensity.
• The number of ejected electrons depends on the intensity of light.
• According to Einstein of the photon is equal to the work function and kinetic .

## Atomic Spectra

A ray of white light splits into a series of colour bands is called a spectrum.

There are two types of the spectrum:

• Emission spectra
• Absorption spectra

### Emission spectra

After absorbing energy atoms or molecules get and when they come back to its ground state they emit certain radiations which produce emission spectra. It is further of two types:

#### Continuous spectrum

Splitting of white light into seven colours after passing through a prism.

#### Line spectrum

After heating a substance at low-pressure light is emitted which on passing through a prism non-continuous spectrum is obtained. Where coloured lines are separated by bands.

### Absorption spectrum

When a beam of white light is passing through a chemical substance the spectrum having a line.

## Hydrogen Spectra

1/λ = RZ2(1/n12 – 1/n22)

where,

λ is the wavelength of the photon

Wavenumber = 1/wavelength

R = Rydberg’s constant (109677)

Z = atomic number of the atom

n1 and n2 are integers where n2 > n1.