Atomic Theory Notes

Atoms look like miniature solar systems

 No one has ever seen an atom and no one ever will.  Atoms are so complex that they cannot be described in terms that laymen can understand. Scientists are constantly learning new things about the way atoms behave and are discovering more and more new particles within the atom. Our concept of an atom resembling a tiny solar system is nothing more than a ‘model’  – in other words, we are trying to describe something we can’t  fully understand in terms of something we can  understand.

Electrons are tiny particles that orbit the atom’s nucleus

Again, this is only a model to help us visualise what ‘might’ be going on inside the atom. In reality, this is unlikely to be the case. Electrons behave both as charged particles  and  as waves. Sometimes, scientists  fi nd it convenient to think of them as charged particles; at other times, they  fi nd it convenient to think of them as waves. In reality, they could be neither but something else completely!

An electric current is always a flow of free electrons

This is only true in the case of metallic conductors, such as copper and aluminium.  This is not necessarily the case in semiconductors, liquids and gases!  A  far better defi nition  of current is that it is a ‘fl ow of charges’.

Current flows at the speed of light

While the  effect  of current within a conductor may be detected more or less instantaneously, individual electrons drift along  very  slowly. Research suggests that an individual electron will not travel the length of a  fl ashlight’s  fi lament within the lifetime of that  fl ashlight’s  battery!

Conductors have lots of free electrons, therefore they must be negatively charged

Although conductors do have large numbers of free electrons, for every free electron, there is a corresponding proton within the atoms or positive ions. So conductors don’t have an overall charge; they are neutral.

Insulators ‘block’ current flow

Insulators don’t ‘block’ current  fl ow; they simply don’t have suffi cient charge carriers to  support current  fl ow.

Insulators contain few free electrons

Insulators actually contain billions of free electrons per cubic millimetre but, compared to conductors, this  fi gure is relatively small and certainly insuffi cient to support current  fl ow.

‘Conventional flow’ is a fl ow of positive charges in the opposite direction to electrons.

No. ‘Conventional  fl ow’ isn’t a  fl ow of anything. It’s simply a ‘direction’, mistakenly chosen, for current, from positive to negative.