Basic Chemistry

Part 2

Quiz Basic Chemistry

Chemical bonds and Carbon, Oxygen, Hydrogen, Nitrogen, Sulfur, and Phosphorus


Because carbon has 4 valence electrons and its electronegativity is close to that of hydrogen and other nonmetals it tends to form 4 covalent bonds equally spaced out around it.

The Lewis structure for methane, CH4 is:


Such formulas help reveal the geometric arrangement of atoms and indicate how electrons are shared.

Because of the constant repulsion due to the electron clouds around the hydrogen atoms of methane the hydrogens end up as far from each other as possible ~ 109°. The shape of the methane molecule is therefore a tetrahedron.

Carbon has the ability to form 3 types of covalent bonds with itself or other elements. These bonds are the:

  • single covalent bond,
  • the double covalent bond which, shares 4 electrons
  • triple covalent bond which shares a total of 6 electrons.

A drawing of the carbon-oxygen double bonds in CO2 illustrates why this molecule must be linear.

Carbon dioxide is nonpolar because of its linear shape. With oxygen at opposite ends, no net difference in charge is possible.

There seems to be no limit to the size of carbon based molecules. A single giant DNA molecule can contain approximately 50 billion atoms. Such giants are called macromolecules. No other element can challenge carbon's ability to form such enormous and diverse molecules.

Carbon atoms in long chains are often referred to as carbon backbones because they support various side groups of atoms that extend from the chains like ribs.

The addition of double bonds in a long carbon chain help to keep it stable. The rigidity created by a double bond prevents the free rotation of any side groups on opposite sides of the double bond.

Fats can be either saturated or unsaturated depending on the presence of double bonds. The difference is illustrated below.

A saturated fatty acid with the molecular formula:


An unsaturated fatty acid with the molecular formula:



Nitrogen generally forms 3 single covalent bonds because is has 3 unpaired electrons in its valance shell.

Nitrogen's 3 unpaired electrons, illustrated on the right, are spaced so that they form a tetrahedron.

The diagram to the left shows that elemental nitrogen is a diatomic gas, N2, but in order to satisfy the octet rule each nitrogen atom shares 6 electrons with its partner, forming a triple bond

Diatomic nitrogen, N2, is unusually stable because a triple covalent bond is extremely hard to break

The structural formula for the ammonium ion, NH4+, shows that one of the 4 hydrogens can enter into a bonding arrangement where it uses the unbonded electron pair of nitrogen, contributing no electron of its own. The positvie charge of the ammonium ion results from the addition of the fourth hydrogen as a proton (see below).

Nitrogen is an essential component not only of amino acids, but also nucleic acids and some carbohydrates, and lipids.

Even though the atmosphere is almost 80% N2 gas it is very difficult for organisms to obtain the element in a usable form. This is because very few organisms were able to evolve an enzyme capable of efficiently breaking nitrogen's triple bond. Only a few species of bacteria are able to fix nitrogen from the atmosphere.

Nitrogen can combine with oxygen gas in automobile engines. This produces nitric oxide (NO). Nitric oxide is a free radical and a major part of photochemical smog. Scientists are only now discovering nitric oxide's numerous roles in physiology.

One recent discovery of a new role for nitric oxide is found in an article called Sperm just say NO to egg cells.


In biological systems phosphorous is always combined with oxygen as a phosphate ion or molecule.

Three important molecules containing phosphate are:

  • ATP - energy exchange
  • phospholipids - structural backbone of cell membranes
  • nucleotides (see below) - subunits in the structure of nucleic acids like DNA and RNA

 The lack of phosphorus has a dramatic effect on the growth and development of plant leaves.


Sulfur is found in 2 of the 20 amino acids which make up proteins. Long protein chains are able to fold up in many ways. But when 2 sulfur atoms line up they can form a stabilizing covalent bond between them.

This bond is called a disulfide linkage or bridge. See Figure below.

The linkage occurs when the hydrogen atoms are removed from adjoining sulfhydral groups.

amino acid S - H + S - H amino acid
amino acid - S - S - amino acid + H2 


A freshman at Eagle Rock Junior High won first prize at the Greater Idaho Falls Science Fair, April 26, 1996. He was attempting to show how conditioned we have become to alarmists practicing junk science and spreading fear of everything in our environment. In his project he urged people to sign a petition demanding strict control or total elimination of the chemical dihydrogen monoxide." And for plenty of good reasons, since:

  1. It can cause excessive sweating and vomiting
  2. It is a major component in acid rain
  3. It can cause severe burns in its gaseous state
  4. Accidental inhalation can kill you
  5. It contributes to erosion
  6. It decreases effectiveness of automobile brakes
  7. It has been found in tumors of terminal cancer patients

He asked 50 people if they supported a ban of the chemical. Forty-three (43) said yes, six (6) were undecided, and only one (1) knew the chemical.

Press here to see if your guess was right.

Page updated July 8, 2005




















Yes, dihydrogen monoxide, or H2O is water. See if you can come up with any other "dangerous" side effects of too much water.