Ozone

What methods can be used to measure changes in ozone?

-Dobson ozone spectrophotometer -total ozone mapping spectrophotometer (TOMS)

Co-ordinate covalent bond

-electrons are shared BUT one member DOESN'T share -intermolecular bond -occurs between atoms or ions of non-metals

Covalent bond

-share valence electrons -intermolecular bond -occurs between non-metals.

Equation for ClO' decomposing

2ClO' --> 2Cl' + O2

What is oxygen composed of?

A diatomic molecule with two atoms joined by the double covalent bonds.

What does ozone have that oxygen doesn't?

ozone is also polar and have stronger intermolecular forces. The donation of the electron pair from the central oxygen atom leaves a small positive charge on the central O atom. Therefore ozone molecules become dipole whereas diatomic oxygen is non-polar.

What is ozone composed of?

ozone molecules have three oxygen atoms, two of them joined by double covalent bonds and one by a single co-ordinate bond.

What are the high MP and BP in ozone due to?

the stronger intermolecular forces in ozone than oxygen. Oxygen has a strong double bond which has more stability than the single co-ordinate bond in ozone, therefore more energy is required to break the O2 bonding than ozone, so the ozone molecule is more reactive than oxygen gas.

Equation for disassociation of CFC's by uv light

CCl2F2 (g) --->CF2CL' (g) + Cl' (g)

Identify origin of chloroflurocarbons and halons.

CFC's and halons are an example of haloalkanes. CFC's were originally developed to replace toxic ammonia as a refrigerant gas, they were considered un-reactive and non-toxic. Thousands of tonnes were made as they were good propellants as well as blowing agents to make polystyrene. CFC's typically contain chloro and fluoro functional groups. They do not contain hydrogen atoms.

What occurs after ClO' is formed

Chlorine free radicals are again released to continue reacting with ozone. Set of chain reactions. Each chlorine atom destroys thousands of ozone molecules before it forms a stable compound and is removed. Each chlorine atom released breaks down an ozone molecule and further reactions release into to break down yet another ozone molecule.

Equation For Chlorine attacking ozone

Cl' + O3 --> Os + ClO'

Equation for ClO reacting with O'

ClO' + O' --> O2 + Cl'

What is a free oxygen radical?

Contains one or more unpaired electrons in its outer shell. The oxygen free radical contains two unpaired electrons in its valence shell.

Example of Haloalkanes

When alkanes react with halogens (group 7), they form a new compound known as haloalkanes. The simplest example is a methane molecule with on of its hydrogens replaced by a halogen such as chlorine. Cl CH3Cl H- C-H H

Ozone in the trophosphere

Is a pollutant. It is a toxic, pungent gas that irritates the eyes and airways, coughing and increased evidence of respiratory conditions such as asthma. It can lower resistance to infections. IT is produced by petrochemical smog which is a problem in many big cities.

total ozone mapping spectrophotometer (TOMS)

Is the name of the satellite instrument used to map global ozone levels.

Other examples of Co-ordinate covalent bonds

NH4+, H3O+

Equation for disassociation of O2 to form O3

O' (gg) + O2(g) --> O3 (g)

Describe the formation of a coordinate covalent bond.

Ozone is a co-ordinate bonded molecule. When elements in groups 5,6,7 form molecules they often retain non-bonding pairs of electrons. These atoms can form additional covalent bonds by sharing their lone pairs with other atoms that need electrons to achieve a full outer shell. Once a co-ordinate bond is formed it is identical to a normal covalent bond.

Effects of CFC's on Ozone

Ozone levels have been decreased in the stratosphere especially over Antarctica over the last 25 years. Ozone concentrations above antarctica are less than other places on Earth due to the polar regions favourable conditions for ozone depleting reactions. The ozone hole which appears of Antarctica each spring is getting bigger. Between 1975 and 1985, it was revealed that ozone concentrations over Antartica had decreased 50%. The hole continues to grow, measures about 24km2 Many areas report thinning is worse in summer. Due to the long lifetime of CFC's the upper atmosphere ozone levels are not expected to show signs of recovery until at least 2030.

Problems associated with us of CFC's

due to being inert, they are able to reach the stratosphere without being changed. Here UV radiation releases a chlorine atom (free radical) from the CFC molecule. AS CFC's rise into the stratosphere, they are disassociated into free radicals by UV light. Also in the stratosphere, O2 disassociates to form the free radical O'. This reacts with O2 to form ozone, O3 The chlorine free radical is extremely reactive and immediately attacks an ozone molecule. The ClO free radical either reacts with a free oxygen radical or decomposes to form another chlorine atom and oxygen gas.

Dobson Ozone spectrophotometer

ground based, uses the sun or moon as a light source, the absorption of different strengths of UV light radiation is measured to present an accurate presentation of the total ozone column.

Ozone in the Strasosphere

in relatively high concentrations reduces the amount of UV reaching the Earth's surface as ozone strongly absorbs UV radiation from the sun. This process is essential for life to continue as UV causes damage to plants and animals by breaking bio-molecules such as protein and DNA which can lead to mutations, skin cancer and damage to the retinas.

How reactive if the oxygen free radical?

Very reactive because it exists in a high energy state and readily reacts with its surroundings. They exist only briefly in the lower layers of the atmosphere. They are more reactive than ozone. It is the most toxic allotrope of oxygen.

Example of Isomers

When a molecule gets bigger, another variation that can occur is in the position of the various atoms. E.g. two molecules of ethane both with two atoms of chlorine. 1,1, dichloroethane 1,2-dichloroethane. Same formula : C2H4Cl2 But different structures and are different compounds. MP and BO would be slightly different and they have two different names.

Development of Halons

developed for use in extinguishing fires particularly in larger computer systems and on aeroplanes. They contain at least one bromo group as well as fluoro groups. Chloro groups may also be present. THey do not contain any hydrogen atoms.

What is an allotrope?

different forms of an element in which the identical atoms are arranged differently so the forms have different properties. Ozone and oxygen gases are both made of oxygen atoms but are arranges differently.

What do ozone and oxygen both have?

dispersion forces between their molecules.