Elements often do not exist in nature in isolation. Instead they exist physically intermixed or chemically bound to one another. It is the same within the human body.









Compounds are formed through the interaction of electrons in the valence energy level.







There are three types of basic mixtures: solutions, colloids and suspensions



Solution


A solution is a mixture subdivided into two parts: the solute and the solvent


The solvent is the substance in the greater amount in which the solute is dissolved.


In salt water the salt is the solute and the water is the solvent.


In solutions the solute is very small. It is invisible to the naked eye.


Since the solutes are so small, they do not scatter light and therefore solutions are transparent.


Since the solutes are so small gravity does not act upon them and they scatter evenly throughout the mixture. Therefore solutions are homogenous.


Once again, since the solutes are so small and gravity does not act upon them, the solutes do not settle out of the mixture.


Colloid


The particles of colloids are larger than solutions but are still invisible.


However, since they are larger they do scatter light and therefore colloids are translucent/cloudy.


The larger particles do not spread evenly throughout the mixture. Therefore, colloids are heterogenous.


Though the particles are larger like in solutions, the particles do not settle out of the mixture.


Suspension

The particles of suspensions are visible. Because of their size, they do not spread through the mixture, and they do settle out of mixture and suspensions are cloudy and heterogenous







When two or more elements are chemically combined a new substance known as a compound is formed. Compounds are created due to the interaction of valence energy level electrons. The basic unit of a compound is a molecule.



Chemical Bonds



There are two types of bonds that form compounds: ionic bonds and covalent bonds. Ionic compounds are generally known as salts and are formed when valence electrons are donated to another atom. Covalent bonds are formed when valence electrons are shared between atoms.







When compounds are formed by the sharing of valence electrons, strong covalent chemical bonds are formed. Notice in the above animation there are two atoms with seven valence electrons (Fl). When each share a single valence electron the octet rule is satisfied for each atom.


Since valence electrons are shared, the atoms remain electrically neutral.



Chemical Bond/Compound Facts



There is potential energy contained within covalent bonds.

When covalent bonds are broken, energy is released (ATP, fossil fuels, etc).


Covalent bonds are relatively strong and ionic bonds are relatively weak.


When ionic compounds are placed in water, they dissociate into positive ions (cations) and negative ions (anions).