Chemical Bonding

Individual uncombined atoms of elements are rarely encountered in the natural world. Most of the substances around us are combinations of elements bonded together in a relatively limited number of ways. The richness of the natural world is due to the remarkable number compounds that result from about 100 elements binding together to form molecules. Chemical compounds are substances that consists of two or more different elements in a definite ratio. For example, water is a compound made up of two hydrogen atoms each bonded to a single oxygen atom. Sodium chloride, NaCl, is also a compound containing one atom of sodium and one atom of chlorine. Wherever you find water, the ratio of two hydrogen atoms to one oxygen atom will always be true, and table salt will always have a sodium atom in a 1:1 ratio with a chlorine atom.

When compounds are not just mixtures of their component atoms. The atoms are actually bonded together and cannot be separated by physical means like distillation, filtering, or with the use of a magnet. In order to return a molecule to its component elements some kind of chemical change needs to occur. When chemical bonding occurs in a diatomic molecule, the resulting compound will always be electonically neutral .

It is primarily the electrons of the atoms that are involved in compound formation. Elements combine to form compounds in two general ways:

Transferring electrons from the atoms of one element to those of one or more other elements to form ionic bonds
Sharing electrons between atoms of different elements to form covalent compounds, also referred to as molecules

There is another type of chemical "bond" that only occurs between molecules that have hydrogen atoms bonded to oxygen, nitrogen or fluorine known as hydrogen bonding. Because hydrogen bonding only occurs between molecules, and does not produce a new molecule, it is fundamentally different from covalent or ionic bonding.

A oxygen, nitrogen or fluorine known as molecular formula shows the composition of a molecule in terms of the numbers of atoms of each element present.

Molecules are three dimensional objects that are depicted in a variety of different ways to emphasize some aspect of their formation or behavior. For example, to understand covalent bonding behavior, it is often useful to keep track of the electrons that are available for bonding. Lewis electron dot symbols are a sort of pictorial shorthand that shows what is known about the bonding behavior of an atom. In a Lewis electron dot symbol, the element's symbol represents the nucleus of that atom as well as the inner or core electrons. These are lower energy level electrons. The outer or valence electrons have the highest energy level and generally, they are the electrons that are involved in forming compounds.

Lewis Dot Diagrams for selected elements

Among the main group elements, the valence electrons are the same as the outer electrons, but among the transition element, some inner electrons may be involved in bonding and are counted among the valence electrons. The dots are arranged around the element's symbol to show the characteristic number of bonds for that element. For example, carbon has 4 valence electrons that are arranged singly around the symbol for the element. When a Lewis Structure is drawn to represent a compound there should be 4 pairs of 2 electrons around each atom following the octet rule and consistent with the general principal that individual atoms tend to seek bonds that produce an arrangement of electrons resembling that of the nearest noble gas.

Depicting Molecules

In order to explore the geometry of a molecule, space-filling and ball and stick models are often used.

A pair of shared electrons can also be represented as a single line joining the two atoms involved in the covalent bond.

Molecular models can show the shape of the molecule, the lengths of the bonds, and the angles the bonds make to one another, although not all of the models show all of these features in the same image. The images here show some of the forms commonly used to depict various features of bonds and molecules.

The periodic table is very helpful in identifying key information about bonding since elements in the same family (column) for main group elements have the same number of valence electrons. For example, all of the alkaline earth elements are found in the 2nd row of the periodic table and they are have 2 valence electrons, and all of the halogens, like F and Cl are found in the 7th column of the main group elements (leaving out the columns containing transition metals) and they all have 7 valence electrons.

Report technical/Content problems here