Carbon, hydrogen, oxygen and nitrogen are known as the main “organic” elements because they form the building blocks that make life possible. Among the four, carbon is the most important element to living things because it can form many different kinds of bonds and form essential compounds. The four classes of macromolecules that make life possible (protein, carbohydrates, lipids, and nucleic acids) are all made of carbon, along with the other three main organic elements.
In a nonliving environment, carbon can exist as carbon dioxide (CO2), carbonate rocks, coal, petroleum, natural gas, and dead organic matter.
Individual carbon atoms have an incomplete outermost electron shell. With an atomic number of 6 (six electrons and six protons), the first two electrons fill the inner shell, leaving four in the second shell. Therefore, carbon atoms can form four covalent bonds to satisfy the octet rule.
The methane molecule has the chemical formula CH4. Each of its four hydrogen atoms forms a single covalent bond with the carbon atom by sharing a pair of electrons. This results in a filled outermost shell. These covalent bonds are called nonpolar covalent bonds because the electrons shared by the adjacent atoms in the bonds are shared equally and the consequence of this equal sharing of electrons is that there is no charge separation.
There is a type of covalent bond called a polar covalent bond. In Biological systems, polar covalent bonds are important because these kinds of bonds allow the formation of another kind of weak bond called a hydrogen bond. Water is an example of a molecule that has polar covalent bonds and engages in hydrogen bonding.
Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the net charge of the compound must be zero.
CHLORIDE SALTS- The sodium atom is donating its 1 valence electron to the chlorine atom. This creates a sodium cation and a chlorine anion. Notice that the net charge of the resulting compound is 0.