Chemistry in a Nutshell

• The Atom
  All macroscopic matter is made out of many tiny particles called atoms.  The study of how these atoms interact is called Chemistry.   
• Subatomic Particles
  The three particles that make up atoms are protons, neutrons, and electrons.   Protons and neutrons are heavier than electrons and reside in the "nucleus," which is the center of the atom. Protons have a positive electrical charge, and neutrons have no electrical charge.  Electrons are extremely lightweight and are negatively charged.  They exist in a cloud that surrounds the atom. The electron cloud has a radius 10,000 times greater than the nucleus. 
• The Nucleus
  The nucleus of an atom is made up of  protons and neutrons in a cluster.  Virtually all the mass of the atom resides in the nucleus.  The nucleus is held together by the tight pull of what is known to chemists and physicists as the "strong force."  This force between the protons and neutrons overcomes the repulsive electrical force that would, according to the rules of electricity, push the protons apart otherwise.
• Electrons 
  The electron is the lightweight particle that "orbits" outside of the atomic nucleus. Chemical bonding is essentially the interaction of electrons from one atom with the electrons of another atom. The magnitude of the charge on an electron is equal to the charge on a proton.  Electrons surround the atom in pathways called orbitals.  The inner orbitals surrounding the atom are spherical but the outer orbitals are much more complicated. 
• Chemical Bonding
  Chemically bonding occurs when two particles can exchange or combine their outer electrons in such a way that is energetically favorable.  An energetically favorable state can be seen as  analogous to the way a dropped rock has a natural tendency to fall to the floor. When two atoms are close to each other and their electrons are of the correct type, it is more energetically favorable for them to come together and share electrons (become "bonded") than it is for them to exist as individual, separate atoms. When the bond occurs, the atoms become a compound. Like the rock falling to the floor, they "fall" together naturally.   

The Periodic Table of Chemical Elements

The periodic table of the chemical elements (also periodic table of the elements or just the periodic table) is a tabular display of the chemical elements. Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.

The periodic table is now ubiquitous within the academic discipline of chemistry, providing a useful framework to classify, systematize, and compare all of the many different forms of chemical behavior. The table has found many applications in chemistry, physics, biology, and engineering, especially chemical engineering.