Cover work Chemistry
An atom is the basic unit that makes up all matter. There are many different types of atoms, each with its own name, mass and size. These different types of atoms are called chemical elements. The chemical elements are organized on the periodic table. Examples of elements are hydrogen and gold. Atoms are very small, but the exact size changes depending on the element. Atoms range from 0.1 to 0.5 metronomes in width. One manometer is around 100,000 times smaller than the width of a human hair. This makes atoms impossible to see without special tools. Equations must be used to see the way they work and how they interact with other atoms.
The word "atom" comes from the Greek ἀτόμος, indivisible, from ἀ-, not, and τόμος, a cut. The first historical mention of the word atom came from works by the Greek philosopher Democritus, around 400 BC. Atomic theory stayed as a mostly philosophical subject, with not much actual scientific investigation or study, until the development of chemistry in the 16 hundred's.
The nucleus is in the middle of an atom. It is made up of protons and neutrons. Usually in nature, two things with the same charge repel or shoot away from each other. So for a long time it was a mystery to scientists how the positively charged protons in the nucleus stayed together. They solved this by finding a particle called a Gluon. Its name comes from the word glue as Gluon act like atomic glue, sticking the protons together using the strong nuclear force. It is this force which also holds the quarks together that make up the protons and neutrons.
Electrons orbit or go around the nucleus. They are called the atom's electron cloud. They are attracted towards the nucleus because of the electromagnetic force. Electrons have a negative charge and the nucleus always has a positive charge, so they attract each other. Around the nucleus some electrons are further out than others. These are called electron shells. In most atoms the first shell has two electrons, and all after that have eight. Exceptions are rare, but they do happen and are difficult to predict.