Modern Atomic Model and EMR

• Describe light in terms of electromagnetic energy.

• Describe the relationship between frequency, wavelength and energy of light.

• Describe line and continuous spectra.

• Explain the formation of line spectra.

• Explain the Quantum Mechanical Model of atoms.

Composed of radiated waves of both electrical and magnetic energy.

Maxwell (1860) - all energy radiated from objects (including visible light) is electromagnetic radiation.

Wavelength (λ - “lambda”): distance from one crest to the next crest or trough to trough.

Frequency (ν – “nu” or ƒ): number of wavelengths, or cycles, that pass a point per unit time.

Frequency is measured in cycles per second (s-1), or the SI unit hertz (Hz).

Amplitude: height of the wave from origin to crest.

Types of Electromagnetic radiation

All EMR radiates at 3.00 x 108 m/s in a vacuum.

This universal value (c) is a product of the wavelength and frequency of the radiated energy.

“speed of light”

c = λνc = λƒ

Wavelength and frequency are inversely related.Wavelength and frequency do not affect amplitude.

Sunlight (white light) shone through a prism separates into a continuous spectrum of colours.

Each colour represents light of a different frequency – increasing frequency - ROY G BIV

Colour Elementgreen copper

yellow sodium

red strontium

yellow-green

barium

orange-red calciumpurple potassium

purple-red lithium

Elements give off a unique colour of light when burned - used to detect the presence of a metal

This is known as a

If the light emitted is focused through a prism, a spectrum with distinct lines is produced.

Planck (1900)

Disclaimer – This is not as simple as my drawing.

Energy emitted by a heated element can be separated – producing emission spectrum.

(line spectrum)

The colored lines of the atoms (or Spectral Lines) are a kind of "signature" for the atoms.

C

O

Spectroscopy and spectrophotometry are techniques used to determine a substance’s emission spectrum

Planck's law: postulated that energy can only be gained or lost in discrete amounts – quanta.

Quantum is the minimum amount of energy gained or lost by an electron.

Energy contained in a quantum was directly related to the frequency of radiation emitted.

E = hf

E = hfE – energy of a quantum (Joules) h – Plank’s constant (6.626 x 10-34 J s)f – frequency of absorbed or emitted EMR

The colours seen in fireworks are a result of burning different salts. Red light has a wavelength of 650 nanometres. Calculate the frequency of red light (1 nm - 1.0 x 10-9 m).

ƒλc =

ƒ 650 x 10-9 m

= 3.00 x 108 m/s

ƒ = 4.6 x 1016 Hz

The blue colour of fireworks is often achieved by heating copper (I) chloride to about 1200oC. The wavelength of the blue light is 450 nm. What is the quantum of energy emitted by this light?

E = hf

ƒ = c λ

ƒ 450 x 10-9 m

= 3.00 x 108 m/s

ƒ = 6.7 x 1014 Hz

E = (6.626 x 10-34J· s)(6.7 x 1014 Hz)

E = 4.4 x 10-19Jq