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 Chemistry Wonder World Q & A - 2. Chemical Bonds of Molecules – Kinds and Functions

© Donald Reinhardt, Sept 18, 2013
 When the simple atoms of various elements chemically combine, they form a compound which has distinct properties. Water (H2O), table salt (NaCl), sodium bicarbonate (NaHCO3), sugar (C6H12O6), carbon dioxide (CO2) and carbon monoxide (CO) are distinct and different compounds that are formed and created as a result of chemical bonding of atoms. Here we explore and discuss molecules and chemical bonds.
 
Chemistry Wonder World Q & A:

Here are just a few things to ask and remember as you study here:

What is the atomic number and why is it important?
The atomic number of an element is the proton number and this determines what the element is and its properties.
The number of protons in an atom always equals number of electrons in a normal element.
If and whenever an element becomes ionized, then the number of protons is not the same as the number of electrons because that ion of the atom has lost or gained one or more electrons.
 How are atoms of metals and non-metals chemically different?
Atoms of elements that donate electrons are called metals.
Atoms of elements that receive donated electrons are called non-metals.
Therefore, the electron-behavior of atoms of metals and non-metals differs. This means that the properties of the metallic and non-metallic elements will vary based on the atomic behavior of their atoms in chemical reactions.

Some atoms of elements, such as carbon, simply share electrons. These atoms of these perticular elements do not give up or donate electrons, they share extra electrons till their electron shells.

Remember this: The electrons in the electron shells are very important for bonding activity. Electrons are involved in the actual bonding process.

Opposite-charged particles and atoms attract and like-charged atoms or particles repel.

Electrons move very rapidly around the central nucleus and chemical reactions often occur very quickly under the right conditions.

The three most important types of chemical bonds are:

Ionic or electrovalent bonds are formed by the process of different atoms donating or accepting electrons. NaCl, NaHCO3 and CaCO3 are examples of ionic-bonded compounds.
Ionic or electrovalent compounds can be identified or known as such by placing them in water and noting whether charged ions form in that solution. A useful test for ions and ionization  typically is to pass a current through an ionized solution and see if the current forms a complete circuit by lighting up a bulb. Also, we can actually measure the presence of a current with some special meters.
Covalent bonds – shared electron bonds – these bonds involve no actual loss or gain of the electrons. H2O, CO, CO2 and C6H12O6 are examples.
Photo: Water molecule with covalently-shared electrons between one atom of oxygen and two hydrogen atoms.
Hydrogen bonds – the attraction of the proton in the nucleus of hydrogen for electronegative charged atoms. Water shows very strong hydrogen bonding. The hydrogens are attracted to the electronegative atoms of oxygen (see  this with an updated flash viewer for diagram of water covalent bonds and hydrogen bonds by clicking here).
 
 
Diagram and Flash Animation Credit: Nicolle Rager Fuller, National Science Foundation
 

What is pH?

pH  is a measure of the hydrogen ion concentration. In pure, distilled water the pH value is 7.0. This represents the log10 of the reciprocal value of the actual hydrogen concentration, e.g., 10-7  (i.e. 1/10,000,000) reciprocated to 107 (10,000,000) = 7. To learn more about pH and understand pH better click here.

What is a chemical reaction and what kinds of chemical reactions are there?

Many chemical reactions are possible. We will only mention and illustrate a few types now for basic understanding.

1. Oxidation and Reduction Reactions.
An oxidation reaction is the addition of oxygen or the removal of electrons or hydrogen from an atom or molecule in a reaction. Reduction is the removal or oxygen from or the addition of electrons or hydrogen to an atom or molecule.

The reactions are called O-R or oxidation-reduction reactions because in the  O-R reaction the oxidizing agent is reduced and the reducing agent is oxidized.

Rusting of iron is a good example here. For the sake of clarity we will illustrate the basic reaction and then balance the reaction atomically.
Fe + O2 ----> Fe2(O3) (iron oxide = rust).
To balnc rusting reaction these are the ac numbers of atoms invloved to form one rust molecule of iron oxide.
4Fe + 3O2 ----> 2Fe2(O3)
Note: 4 iron atoms react with 3 oxygen molecules (total of 6 atoms of oxygen) to yield 2 iron molecules

In the above example, what is oxidized? What is reduced?

Here is an example of hydrogen gas reacting with oxygen in an explosive reaction:

H2 + O2 --à H2O + light + heat

2. Exchange and Substitution Reactions.
In an exchange-substitution reaction, two compounds are mixed and the molecules or ions  in the solution react and interact in such a way that two new compounds are formed.

A good example of an exchange-substitution reaction is the mixing of an acid and a base in solution, as with hydrochloric acid (HCl) and sodium hydroxide (NaOH)  which when mixed will yield salt and water  as shown here: HCl + NaOH-à HOH and NaCl.