Chemistry 1020--Lecture 4--Notes
Ozone: both a curse and a blessing: It is toxic, more reactive than oxygen, and damages tissues of both plant and animal life. It is produced in electrical discharge, but as a pollution problem in the local atmosphere, it is a byproduct of photochemical reaction of automobile exhaust products: nitrogen oxides and volatile organic compounds produced by incomplete combustion of hydrocarbons. But in the stratosphere it serves to protect the earths surface from damaging ultraviolet radiation from the sun.
Work on ozone production and degradation in the stratosphere was recognized by the 1995 Nobel Prize in Chemistry. Visit the web site describing the work leading to the prize and the recipients.
Therefore we need a brief introduction to:
Atomic Structure (protons, neutrons, electrons)
Molecular Structure (Lewis dot model for describing)
Electromagnetic Radiation (Spectrum of energies; interaction with matter)
Following this introduction, we can begin to understand the structure and reactivity of chlorofluorocarbons, and their role in ozone depletion.
Atomic Structure (proton, neutron, electron model)
The mass of an atom is concentrated in a tiny nucleus. The nucleus is composed of particles called protons and neutrons. Protons are positively charged, neutrons are neutral, and electrons are negatively charged. Atoms are of the order of size of 10-10 meters (1 angstrom) in diameter, while nuclei are about 10-14 meters. Compare a quarter to the size of the University Center around Cambell Stadium.
Relative masses: p = 1, n = 1, e = 1/1838
Relative charge p = +1, n = 0, e = -1.
The atomic number of an element gives the number of protons and the number of electrons in a neutral atom. It is the property distinguishing one element from another.
Isotopes are atoms of the same element having different masses.
Electrons arranged in shells around the nucleus. (Discuss the inability to determine the exact path of an electron).
First shell can hold only 2 electrons. Second shell can hold 8. Third shell can hold 18, but something special about the first 8 which form a subshell of the third shell.
Consider only the first three periods of the periodic table.
Symbolize structure of an element as follows:
A = mass number = n + p
Z = atomic number = p = e
q = charge = p-e
n = number of atoms in unit
Try calculating composition of several elements.
Lewis Dot Structures: represents outer shell electrons as dots around the symbol of the atom. (Draw Lewis dot representations of above elements). Elements of a family have in common the number of outer shell electrons (called valence electrons).
Compounds form because elements want to gain a stable octet of electrons. Can do by gaining or losing electrons, or by sharing.
Gaining and losing electrons forms ions. Explains ionic composition of compounds between IA or IIA and VIA or VIIA elements. (Illustrate formation of ions of these groups using Lewis structures).