How atoms work
Atoms are the tiniest piece of any element that cannot be chemically subdivided by ordinary method. The origin of this word is from Greek where atom means indivisible. Greeks are very famous for their thinking skill and it was the Greek brain Democritus, who first proposed that something could be cut into its smallest pieces and still be the same thing. It took another few thousand years to invent the proper instrument to prove his theory. By the way, hydrogen was the earliest atom formed when quarks and an electron stuck together shortly after the Big Bang.
Before discussing how atoms work, let us take a short shot inside the atom.
Atoms are made of three types of particles: Electrons, Protons and Neutrons. In other word electrons, protons and neutrons make the Universe go! There are even smaller particles inside protons and neutrons, these super particles are called nucleons and quarks.
How these components of atoms are packed inside? There are many theories regarding atomic structure. The simplest one is called Bohr model proposed by Danish Physicist Neils Bohr. According to Bohr's model, nucleus consisting of positively charged protons and neutral neutron stays stationary at the core of an atom and around it are whizzing equal number of negatively charged electrons in orbits that have quantized energy that means when electron jumps from one orbit to another it must absorb or emit energy of photon. His theory later opened a new branch of particle physics called Quantum Mechanics.
The mass of an atom is the mass of its nucleus that is the sum of neutrons and protons. Numbers of protons in a nucleus never change but number of neutrons can change.
Two atoms with same number of protons but different number of neutrons are called isotopes. Hydrogen has one proton in its abundant form but it's isotope deuterium has one proton and one neutron in its nucleus.
When atomic nucleus contains as many neutrons as protons, it is stable. However when it has more neutrons than protons it becomes unstable. The nucleus of such an unstable atom tries to become stable by giving off particles or packets of energy called quanta. These emissions are called radioactivity.
How electrons are organized around the nucleus?
All atoms tend to attain the configuration of noble gas elements (i.e.8 electrons in it's outer shell). This is the basis of all chemical reaction. Atoms can form noble gas configuration in its outer shell through
1. Losing electron
2. Gainig electron
3. Sharing electron.
For example, Oxygen (O) has 8 electros in total.
The electronic configuration of Oxygen can be written as 1s2 2s2 2p4.
In its second energy level, which is the valence shell it has 6 electros and needs 2 more to attain stable configuration. Hydrogen has 1 electron and needs I more to attain the structure of noble gas Helium. The chemistry behind the formation of water is to satisfy their need of stable configuration by sharing their valence shell electrons.
What is the theory behind atomic explosion that is atom bomb?
Of course Einstein's theory of relativity E= MC2. Enrico Fermi invented apparatus that can carry out chain reaction and the result is Manhattan project. Consequence? Hiroshima and Nagasaki. When an atom of Uranium -235 or Plutonium is split under the influence of a single neutron an immense release of energy occurs. The splitting also shoots of more highly energetic neutrons that can hit more atoms in self-sustaining sequence. The whole process is distracting the nuclear force. This is different from chemical reaction.