Questions you may have about this are:

What does Chemistry all about?

What are important characteristics of atoms?

What is the solar system model of an atom?

What rules do electrons have?

What determines chemical reactions?

The following material gives a starting point for the study of Chemistry. You will learn what is an element, what is a compound, what are the characteristics of an atom and its nucleus

Chemistry is about making materials

Most of the study of Chemistry concerns the combining of different substances to form new materials. These substances may be anything from simple atoms or elements up to highly complex molecules. Any of those substances—elements or molecules—can be called chemicals.

Elements or atoms

A chemical element is a substance made up of a specific type of atom. This is as opposed to a compound which is made up of combinations of atoms joined as molecules. Usage of the words element and atoms are interchangeable.

All the elements occurring in nature have been named and are given shorthand symbols to represent them. Examples of elements are: Hydrogen, Helium, Carbon, Oxygen, Iron, Gold, and Sulfur. Their shorthand symbols are, respectively: H, He, C, O, Fe, Au, and S. Some symbols represent the name, while others stand for the Latin version of the name.

There are 92 natural elements. Number 92 is Uranium. There are also several that have been created artificially, but they disintegrate rapidly.

Compounds or molecules

Chemical compounds are combinations of elements. A chemical compound is a molecule. The words compound and molecule are essentially interchangeable. Molecular forces hold compounds together.

The Carbon Dioxide molecule is an example of a compound. It is a combination of the elements Carbon and Oxygen.

There are certain forces and rules that dictate what combinations of elements combine.

Rules for electrons in orbit

Although the electrons rotate around the nucleus, similar to the planets around the sun, there are usually more than one electron in an orbit, as opposed to our Solar System. In fact, there are rules for the maximum number of electrons in each orbit, which are also called shells or levels in Chemistry.

A maximum of 2 electrons are allowed in the first orbit. For example, Hydrogen has 1 electron and Helium, which is atomic number 2, has 2 electrons in the first orbit or shell.

The maximum number of electrons in the second orbit is 8. Element number 3, Lithium has 2 electrons in the first orbit and 1 in the second orbit. Neon, number 10, has 2 electrons in the first orbit and 8 in the second.

The third orbit has a maximum of 18 electrons and the fourth orbit can have no more than 32.

The electrons must usually fill up the lower orbits before starting on a higher orbit.

Result has new properties

Chemistry is the study of how and why various elements combine to form molecules, as well as how molecule will also combine to form new materials.

The interesting thing is that the molecule formed by the combination of other materials usually has completely different physical and chemical properties than the original materials. For example, combining the explosive Sodium (Na) with the poisonous green Chlorine (Cl) gas will result in the white crystalline Sodium Chloride (NaCl) or table salt.

Outer shell determines reactions

The chemical combination of elements to form a molecules is based on the number of electrons in the outer orbit or shell of the element. One rule states that each atomic shell has a maximum allowed electrons, with 2 for the first shell, 8 for the second, and so on. Another rule states that elements "like" to have their outer orbit either filled or empty of electrons.

Thus, chemical compounds are formed when elements can trade or share electrons in their outer orbits, such that the shells or each element are either filled to the maximum or completely empty. In the case of NaCl, Sodium gives up its one outer electron to fill the Chlorine's outer shell.

Chemical reactions concern outer orbits

The essence of chemistry relates primarily to the outer orbits of the elements involved. In other words, chemical activity is determined by the number of electrons in the outer orbits of the atoms. Those electrons are often called valence electrons.

In conclusion

Chemistry is about the combining of elements or molecules to form new molecules with completely different characteristics. The number of electrons in the outer orbit determines whether materials will chemically combine.