Subatomic particles The nucleus The electrons The atom

Atoms are the basic building blocks of matter. Every thing is made of atoms, rocks, living things, the Earth, the stars, all that we can see. What are atoms made of?

Click for larger imageSubatomic particles
The modern quantum atomic theory of the atom states that all atoms have three fundamental parts (or subatomic particles): protons, neutrons and electrons. All three can exist by themselves, but it is when they combine to form atoms that they become truly spectacular in their behavior.

The nucleus
The protons and neutrons are found tightly bound into a very small, positively charged, central core called the nucleus. In the average size atom, the nucleus takes up 100 000th of the diameter of the atom. If the nucleus of an atom was the size of a marble, then the atom it belonged to would be about the size of the a football ground. The nucleus is so dense that if the marble in the middle of the ground was made of only protons and neutrons it would weigh about 1 000 tonnes.

This extremely small, very dense centre of the atom has nearly all of the atom's mass and is virtually indestructible in everyday chemical and physical reactions. It is only in the stars, nuclear reactors, atomic bombs and during radioactive decay that nuclei can be broken and reformed.

The electrons
The nucleus is surrounded by a "cloud" of very fast moving electrons. In contrast to the nucleus, this vast empty space has virtually no matter in it and hence no mass. The light weight electrons can move very fast, some thousands of kilometres per hour, and act a bit like the blades of a fan. When the fan is stopped, you can see the spaces between the blades but, when it is full on, the blades and space blur together and the blades effectively occupy all the available space.

The electrons are arranged in energy levels and orbitals, or regions in space where electrons can be found. Scientists describe the arrangement of electrons using mathematics and "quantum numbers" which uniquely describe the shape of each orbital and the properties of each electron, the modern quantum theory goes on to describe a strange subatomic world of wave/particles and electromagnetic energy.

The quantum atom

The atom
There are over 100 known types of atoms in our Universe, all made up of the three subatomic particles. Each type of atom is identified primarily by the number of protons it has in its nucleus; for example, the hydrogen atom has 1 proton, while the uranium atom has 92 protons. The number of protons an atom has is specified by its "Atomic Number", and it is by using atomic numbers that scientists can arrange the atoms into some order.

Each atom will also have just enough neutrons to hold all the protons together in the nucleus. The presence of the neutrons allows two fundamental forces, the weak and strong nuclear forces, to come into play and form the tightly bound atomic nucleus.

The atom is made complete by adding the same number of electrons as it has protons. This makes the whole atom electrically neutral. The electrons are much more weakly bound to the atom and can move from one atom to another or even be "rubbed off" an atom. Static electricity is created by electrons rubbing off atoms and moving to other atoms. It is these electrons which form the basis for chemical change and the diversity of materials and substances we have in our modern world.

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