<span>Several
important pollutants are produced by fossil fuel combustion: carbon
monoxide, nitrogen oxides, sulfur oxides, and hydrocarbons. In addition,
total suspended particulates contribute to air pollution, and nitrogen
oxides and hydrocarbons can combine in the atmosphere to form
tropospheric ozone, the major constituent of smog.
Carbon monoxide is a gas formed as a by-product during the incomplete
combustion of all fossil fuels. Exposure to carbon monoxide can cause
headaches and place additional stress on people with heart disease. Cars
and trucks are the primary source of carbon monoxide emissions.
Two oxides of nitrogen--nitrogen dioxide and nitric oxide--are formed in
combustion. Nitrogen oxides appear as yellowish-brown clouds over many
city skylines. They can irritate the lungs, cause bronchitis and
pneumonia, and decrease resistance to respiratory infections. They also
lead to the formation of smog. The transportation sector is responsible
for close to half of the US emissions of nitrogen oxides; power plants
produce most of the rest.
Sulfur oxides are produced by the oxidization of the available sulfur in
a fuel. Utilities that use coal to generate electricity produce
two-thirds of the nation's sulfur dioxide emissions. Nitrogen oxides and
sulfur oxides are important constituents of acid rain. These gases
combine with water vapor in clouds to form sulfuric and nitric acids,
which become part of rain and snow. As the acids accumulate, lakes and
rivers become too acidic for plant and animal life. Acid rain also
affects crops and buildings.
Hydrocarbons are a broad class of pollutants made up of hundreds of
specific compounds containing carbon and hydrogen. The simplest
hydrocarbon, methane, does not readily react with nitrogen oxides to
form smog, but most other hydrocarbons do. Hydrocarbons are emitted from
human-made sources such as auto and truck exhaust, evaporation of
gasoline and solvents, and petroleum refining.
The white haze that can be seen over many cities is tropospheric ozone,
or smog. This gas is not emitted directly into the air; rather, it is
formed when ozone precursors mainly nonmethane hydrocarbons and nitrogen
oxides react in the presence of heat and sunlight. Human exposure to
ozone can produce shortness of breath and, over time, permanent lung
damage. Research shows that ozone may be harmful at levels even lower
than the current federal air standard. In addition, it can reduce crop
yields.
Finally, fossil fuel use also produces particulates, including dust,
soot, smoke, and other suspended matter, which are respiratory
irritants. In addition, particulates may contribute to acid rain
formation.
Elements in one row of the periodic table have the same energy levels. A row on the periodic table is the horizontal arrangement of elements. These rows are called periods.
There are 7 periods on the periodic table.
Each elements on a period begins with an atom having one valence electrons and then ending with completely filled orbitals.
Elements in the same period are known to have the same electronic shells which is the energy level.
The principal quantum number of their electrons is the same.
Elements that are in the same period have chemical properties that are not all that similar. Consider the first two members of period 3: sodium (Na) and magnesium (Mg). In reactions, they both tend to lose electrons (after all, they are metals), but sodium loses one electron, while magnesium loses two.
There are a total of four quantum numbers that govern the
electrons. These are the principal quantum number (n), the angular quantum
number (l), the magnetic quantum number (ml) and lastly the spin quantum number
(ms). Each electron has a unit set of the four quantum numbers.
Since the first 3 quantum numbers is already specified, so
the remaining to be filled is the ms quantum number which can only have values
of +1/2 and -1/2. So we have 2 electrons.
