Online lesson chemical bonding done by Javier Toh

My Dot and Cross diagram >>

The harmul compound which i have found is Sulfur dioxide.
Sulfur dioxide is a harmul compound made up of sulfur and oxygen which are harmless elements.
Sulfur dioxide undergo covalent bonding as both elements sulfur and oxygen are non-mestal.

Environmental Effects: Sulfur dioxide and nitrogen oxides are the major precursors of acid rain, which has acidified soils, lakes and streams, accelerated corrosion of buildings and monuments, and reduced visibility. Sulfur dioxide also is a major precursor of fine particulate soot, which poses a significant health threat

Sulfur Dioxide:

It is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain.

Sulfur:

It is an abundant, multivalent non-metal. Sulfur, in its native form, is a bright yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals. It is an essential element for life and is found in two amino acids: cysteine and methionine. Its commercial uses are primarily in fertilizers, but it is also widely used in black gunpowder, matches, insecticides and fungicides.

Oxygen:

In nature, oxygen is a gas with no color or smell. Oxygen is a very important element because it is a part of the air you breathe and the water you drink. Because of this, oxygen supports life. All living things (including humans) need oxygen to live , and is a highly reactive nonmetallic element that readily forms compounds (notably oxides) with almost all other elements

The effects of sulfur dioxide are:

• It is the major component of acid precipitation
• It corrodes metals
• It is toxic to plants
• It combines wit moisture in the nose and lungs to create irritation

sources:
http://www.cleanairtrust.org/sulfurdioxide.html
http://wiki.answers.com/Q/How_is_how_is_sulphur_harmful#ixzz1DnklgZw1 http://en.wikipedia.org/wiki/Oxygen
http://simple.wikipedia.org/wiki/Oxygen http://en.wikipedia.org/wiki/Sulfur http://en.wikipedia.org/wiki/Sulfur_dioxide