Werner Heisenberg (1926)

Heisenberg was a German theoretical physicist and is known as one of the pioneers of quantum mechanics.

The combined efforts of Schrodinger and De Broglie


Showed that electrons behave both like waves and particles


This led to Heisenberg’s uncertainty principle

Which states that you can never know the exact position or speed of an object

because everything in the universe acts as both a particle and a wave at the same time.


This is because particles exist in one specific location, but a wave is a transfer of energy through a medium

Ripples in Water

so a wave can not be described in one specific location only in probabilities of locations.


Waves can be described via wavelengths which is the distance between crests on the wave shown above.

This wavelength is proportional to the speed of the wave by the equation

velocity = wavelength * frequency

In summary, waves can be described by their wavelength which is proportional to their speed, and particles can be described by their position.

In newtonian physics the objects being measured are so large, that their wavelengths become impossible to detect, and this is why the wave properties of matter are unobservable in everyday life.

But once in the quantum level or when dealing with really really small things objects begin to display both their wavelike properties and their particle like properties.

The Basis of the Heisenberg Uncertainty principle:

 it is impossible to observe both the wavelike (speed) and particle like (position) properties of an object accurately at the same time.  The more accurate you get in measuring one the more uncertain the other.

Therefore, the exact position of an electron can not be described.

This makes the Bohr Model, which describes the motion of electron’s in neat orbits obsolete.

What has replaced the Bohr Model is the Quantum Model or the Cloud Model


This model takes into  account the different energy levels described by Bohr, but within these energy levels

are molecular orbitals.


which are regions of space where electrons are most likely to be found.

These orbitals of different atoms interact with each other, and form the covalent/ ionic bonds we are familiar with.


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