Untitled

Bohr's Study of Spectra

• When white light from an ordinary electric bulb it is broken up into an array of colours called a continuous spectrum.
• When the same experiment is carried out with a hydrogen discharge tube it produces an emission line spectrum. A hydrogen discharge tube is a tube containing hydrogen gas at a low pressure through which an electric current is passed.
• The emission line spectrum of an element is characteristic to that element.
• Spectra are usually studied using a spectrometer or a hand-held spectroscope.
• Everyday we see that different elements emit different colours when an electric current is passed through them. Eg. sodium street lamps give off a yellow colour, neon advertising signs glow red.

Flame Tests

• Stick a damp wooden splint in a petri dish of each of the following metals : Barium, Sodium, Copper, Lithium, Strontium and Potassium. ( Little Peter Buys Sweets Chocolates and Soft Drinks.
• Lithium turns the flame red.
• Strontium turns the flame crimson. ( a strong colour.)
• Barium turns the flame green ( an irish bar!)
• Potassium turns the flame lilac. ( P for Purple)
• Copper turns the flame blue-green ( like old buildings)
• Sodium turns the flame yellow. (like sand)

Slide 3