The atoms in most molecules are held together by strong forces of attraction called chemical bonds. These bonds are formed through the interaction of the valence electrons of the atoms that combine. In addition to the very strong forces within a molecule, there are weaker forces acting between the molecules. Every atom contains negatively and positively charged particles (electrons and protons).
Atoms are the smallest part of a chemical element that can be obtained. There are things smaller than atoms (for example, particles or quarks), but they do not represent any type of element (just as screws and gears are not real motors, but a part of them). An atom is composed of a nucleus, which includes protons and neutrons, and an electron shell. Interactions between electrons from different atoms (by exchange or sharing, for example) result in chemical bonds.
The union between atoms is called a molecule. Atoms are made up of 3 different smaller particles: protons, neutrons and electrons. Atoms form chemical bonds with other atoms when there is an electrostatic attraction between them. This attraction is the result of the properties and characteristics of the outermost electrons in atoms, which are known as valence electrons.
For example, there is no barrier around the nucleus of an atom. An atomic nucleus is a group of protons and neutrons. The strength of these interactions between charged particles can be modeled using an equation, Coulomb's Law. In 1908, Ernest Rutherford conducted an experiment in which he projected beams of radiation through a sheet of gold that is made up of gold atoms.
Before microscopes were invented, scientists experimented to learn about the structure of an atom. When two atoms, or two molecules (or two particles composed of atoms or molecules) approach each other, they will eventually come close enough so that the repulsions between similar charges are stronger than the forces of attraction between different charges. If you get far enough away and away from Earth, the interaction won't be enough to keep you attracted to the Earth and you'll keep moving away forever. But this attraction has its limits: when atoms get close enough together, the interactions between the negatively charged electrons (and the positively charged nuclei) of each atom increase very rapidly, leading to a general repulsion that will prevent the two atoms from getting so close.
These energy changes are responsible for the formation of molecules, for their reorganization through chemical reactions and for the macroscopic properties of chemical substances (that is, what does all this have to do with atoms getting closer to each other? We can use the same type of reasoning to understand the energy changes that occur when atoms approach each other. We can identify (and calculate) the types of energy changes that occur when particles interact. Unlike kinetic energy, the potential energy in a system also depends on the force acting on it, and that force is a function of the position of the interacting objects within the gravitational field. Because the tunneling scanning microscope is so powerful, you can see tiny spheres that are iron atoms (the smallest possible iron unit).
The atom has no net electrical charge since the number of electrons is equal to the number of protons.