Particles in atoms

The atom is the basic unit of matter. Atoms are too small to be seen except by very sensitive instruments such as scanning tunnelling microscopes. The picture shows an image of atoms of the metal nickel generated using scanning tunnelling microscopy.

Scientists in the early 1900's showed that atoms are composed of particles having the properties given in the table.
 
particle name relative mass*relative charge*
proton (p+)1+1
neutron (n0)10
electron (e–)0.0005–1
*The ACTUAL mass of particles in the atom is VERY small
(0.0000000000000000000000016 g). 

Likewise the actual charge on these particles is very small.

It is convenient to quote the mass of the proton, neutron and electron relative to the atomic mass unit. Similarly, the charges on these particles are quoted relative to the charge on the electron ( -1).  
 
Further experimental results are consistent with a model of the atom in which a positively charged nucleus (orange at the right) is surrounded by an electron cloud.
 
The nucleus contains both protons and neutrons and contains most of the mass of the atom.  These particles are known as nucleons.

The electrons are in constant motion about the nucleus. The electron cloud shows the region in which the electrons are likely to be found. The nucleus is very very small in comparison to the electron cloud.
Move your mouse over the electron cloud to see a much expanded view of the nucleus.
Dr Sheila Woodgate
© The University of Auckland 2002