Atoms are thought to be the smallest entities which take part in the chemical reactions. They join with each other in different ratios to form the molecules which then combine to form macro-molecules. The molecules can exchange atoms with other atoms or molecules to give rise to different molecules.
Atoms are not the fundamental particles of the matter. Even an atom contains protons and neutrons confined in a very small space called nucleus in the core of the atom and electrons occupy rest of the space. Electrons are negatively charged particles and counter balance the positive charges on the protons in the nucleus. Since their charges are equal and opposite, their number are identical. There are neutrons also which are similar to protons in the weight but have no charge.
Now come the puzzling bits. how do the electrons orient themselves inside a atom. If they are really the particles as we think then they must be having a definite volume. Since we say that the space occupied by the electrons is many times bigger than nucleus and size of electrons is very small, then there must be some empty spaces inside the space outside nucleus. The question is if this is so then what is there which occupies that space. Is it a vacuum?
All these observations force us to conclude that reality is much more complicated than we think. It is usual in the science to construct the simplified models which are capable of explaining a certain set of data. That is why the concept of matter and wave duality was propounded. According to this principle, entities behave both as particle and wave simultaneously. This has been proved in famous experiments in which electrons behave as waves. The famous equation governing this wave nature is Schrodinger’s equations.
Similarly, it is fundamental truth that particles with similar charges repel each other. Then how come are many positively charged protons are crammed into such a small volume. Why do not they fly apart? Why is the arrangement quite stable with nucleus remaining unchanged for years. Again the things are not what they are thought to be. It has now been proved that even protons and neutrons are not the fundamental particles but are made of strange type of particles called Quarks. It has been found that mass of the nucleus is not equal to aggregate mass of protons and neutrons it contains. It is lesser than that. Where is the mass that is lost. It is present in the form of energy and amount of energy is according to Einstein’s equation E=mass multiplied by speed of light squared.
That is why we are making atom smashers where we break apart the atoms by bombarding them with particles approaching speeds of light and analyze the particles which are formed during collision.