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Bohr's theory

Electrons occupy the lowest available energy levels. The electrons are in their ground state.

When energy is given to an electron (either by heating or electricity), electrons are promoted to higher energy levels. They are in their excited state.

The excited state is unstable and temporary. Electrons fall back to lower energy levels, emitting energy as light.

The energy difference between levels gives a specific frequency.

Conclusion: Because only specific frequencies are emitted, electrons must be restricted to certain specific energy levels.

Flaws in Bohr's Theory

Only successful in explaining hydrogen. Even helium is too complex.

Some of the bright lines were double or triple lines (sublevels)

Wave-particle nature of matter had not yet been discovered.

The uncertainty principle had not yet been stated.These had to be incorporated into any model of the atom.

Louis De Broglie suggested that all moving particles had a wave motion associated with them. This was proved correct.

Heisenberg's Uncertainty Principle states that it is impossible to measure at the same time both the velocity and the position of an electron.

An orbital is a region in space within which there is a high probability of finding an electron

All 's' orbitals are spherical and only differ in size.

All 'p' orbitals are dumb-bell shaped

Experiment : Carry out flame tests with salts.

Dip the nichrome wire in the HCl to clean it.

Dip the nichrome wire in the salt to be tested.

Hold the nichrome wire in the bunsen flame

Note the colour

Results :

Lithium - Crimson

Sodium - yellow

Potassium - Lilac

Barium - Green

Strontium - Red

Copper - Blue/Green

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