Basic Chemistry: a re-introduction
Here is a quick review of some very basic chemistry concepts, which are common to all biology courses. You should be familiar with this information, and be prepared for it to appear on any test or quiz.
Let's start with the basics:
All matter is made of Atoms, and Atoms are the basic unit of structure of all matter.
Atoms are made up of sub-particles (Protons, Newtons and Electrons) that are organized into two parts:
Atom, showing parts
Atoms are bits of matter that cannot be subdivided any further without losing essential properties
Element are substances that cannot be broken down chemically into any other substances. Example: Oxygen, Nitrogen, Hydrogen
Molecules are when two or more atoms are chemically combined.Example: O2, H2O, C6H12O6
The properties of a Molecule are determined by the shape.
Water has a distinctive shape (the Hydrogen atoms bonded to the oxygen are separated by 120o).
The shape of the Water Molecule determines its properties.
Waters molecular shape gives each molecule a slightly Positive charge (Hydrogen)
and slightly Negatively charge (Oxygen) side.
These slight static charges, cause water molecules to stick together.
Water Molecule, showing atoms and electrons
Types of Bonds:
Chemical compounds are formed by the joining of two or more atoms. A stable compound occurs when the total energy of the combination has lower energy than the separated atoms. The bound state implies a net attractive force between the atoms ... a chemical bond.
There are two main types of chemical bonds:
Covalent bond: bond in which one or more pairs of electrons are shared by two atoms.
Ionic bond: bond in which one or more electrons from one atom are removed and attached to another atom, resulting in positive and negative ions which attract each other.
These are the bonds that form the chemical compounds andmolecules that form the materials areound us.
Another type of bond that results in the properties of molecules is the Hydrogen Bond.
The dashed lines are the Hydrogen Bonds between water molecules.
Water is H2O: Two Hydrogens and One Oxygen. The Oxygen Molecules (Red)
in this diagram are attached by covalent bonds to the Hydrogen molecules
(White). The dashed lines represent the Hydrogen Bonds - the weak attractive
force between the positive Hydrogen atoms and the negative Oxygen.
These charges are unevenly distributed because of the shape of the molecule.
These are Hydrogen Bonds, which give water many of its characteristic properties, including:
Cohesive property - water molecules stick together because of slight static electrical charges called Hydrogen Bonds
Adhesive property - water molecules can stick to many solids because of these same Hydrogen Bonds
Water is LESS Dense as a solid than a liquid - Hydrogen Bonds cause water molecules to arrange into a crystal lattice as it cools
Water is a "Universal Solvent" - Water is capable of dissolving a variety of different substances. Water dissolves more substances than any other liquid. This is important to every living thing on earth.
Essential Properties of water:
This short video will illustrate these essential properties of water:
A combination of waters' properties cause water to exhibit Capillary Action.
Capillary action is the result of adhesion and surface tension. Adhesion of water to the walls of a vessel
will cause an upward force on the liquid at the edges and result in a meniscus which turns upward.
The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the
whole liquid surface is dragged upward. Capillary action occurs when the adhesion to the walls is
stronger than the cohesive forces between the liquid molecules.The height to which capillary action will
take water in a uniform circular tube is limited by surface tension. The illustration to the right shows
the cappilarry force pulling the water higher in the narrow tube.
Surface Tension is responsible for droplets of water tend to be pulled into a
spherical shape by the cohesive forces of the surface layer. The spherical shape minimizes
the necessary "wall tension" of the surface layer. Surface tension is a contractive tendency
of the surface of a liquid that allows it to resist an external force.
Water's Hydrogen Bonds are strongly attracted to polar substances, and repelled by non-polar substances.
This attraction is called Hydrophilic attraction (Hydro = Water, Philia = Love of, or attraction).
The repulsion is called Hydrophobic (Hydro = Water, Phobia = fear or repulsion).
Hydrophillis and Hydrophobia are attributes of water that are caused by the static electrical charges of the molecule due to the uneven distribution of the (negative) electrons.
A solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, the solvent
The Solute is the dissolved matter in a solution. The Solute is the liquid that it is dissolved in.
The most common solvent in everyday life is water. Water is considered a "Universal Solvent" because it can dissolve more materials than any other known liquid.