Chemistry & Environmental Dictionary

Periodic Law - PVC

Periodic Law

The electron configurations of the atoms of the elements vary periodically with their atomic number. Consequently, all properties of the elements that depend on their electron configuration tend also to change with the increasing atomic number in a periodic manner.

Periodic Table

an arrangement of elements in a geometric pattern designed to represent the periodic law by aligning elements into periods and groups. Elements with the same number of orbitals are in the same period and elements with the same number of electrons in the filling orbital and have other similar properties are in the same group.


While groups are characterized by the number of electrons present in the outer shell, periods are characterized by the number of energy levels (shells) of electrons surrounding the nucleus. Elements in Period 1 has only one shell. As you probably recall, the elements in the first period have a 2 electrons maximum (hydrogen has 1 electron and helium has 2 electrons. As we move to the first group of the second period, we find that lithium, which has the two electrons in the first shell and one in the second. Neon is in Group 18 of Period 2 and therefore has the two electrons in the first shell and eight electrons in the second shell. Sodium starts Period 3 with 11 electrons, two in the first shell, eight in the second shell and one in the third shell. In other words, the element in Group 1 always has one more electron (in a new shell) than the Group 18 element in the previous period.


Lining of the abdominal organs and cavity.

Permissible Exposure Limit (PEL)

The maximum allowable exposure set by OSHA under the Code of Federal Regulations Title 29 Section 1910, Subpart Z.


A scale ranging from 0 to 14, which is used to determine how acidic or basic a substance is. The pH of a substance is determined by taking the negative of the logarithm of the molar hydrogen-ion concentration (pH=-log [H+]). Pure water has a pH of 7. Substances with a pH less than 7 are acids and substances with a pH greater than 7 are bases.


discrete concentrations of energy that move at the speed of light, have no rest mass and can only be described in mathematical terms. The quantum unit of electromagnetic radiation that makes up light waves, gamma rays, x-rays etc.


The thin membrane enveloping the lungs and lining the thoracic cavity.

Pleural Effusion

Presence of fluid in the pleural cavity resulting from excessive transudation or exudation from the pleural surfaces. It is a sign of disease and not a diagnosis in itself.

Pleural plaques

areas of fibrosis present on the inner surface of the ribcage and the diaphragm. They may be partly calcified


a warning sign measuring 10.8 inches on each side and standing on one point (like a diamond), that is placed on the four vertical sides of the truck, rail car, intermodal container or two sides of an intermediate bulk container containing hazardous materials. Placards are required by the USDOT, Transport Canada, Secretariat of Transport (Mexico) and other regulatory agencies around the world when shipping hazardous materials by air, highway, rail or water. More information


a condition characterized by deposition of large amounts of particulate matter or fibers in the lungs, usually of occupational or environmental origin, and by the tissue reaction to its presence.


a positively charged particle of antimatter that has the same mass and spin of an electron.

Principal Quantum Number

A positive integer constant that determines the principal energy level of an electron. Sometimes it is designated by the letters K, L or M. Related information


In measurement indicates a set of measurements that are very similar. They may or may not be close to the true answer.


A particle of matter with a positive electrical charge and a mass of 1 amu or 1.67E -24g. Although a proton has a mass 1837 times greater than an electron, it is nearly identical in mass to a neutron. Protons are constituents of the nuclei of all elements and an elements atomic number is dependent upon how many protons an element has.

Pulmonary Fibrosis

Chronic inflammation and progressive fibrosis of the pulmonary alveolar walls, usually results in death from oxygen lack or right heart failure.

PURPA (Public Utilities Regulatory and Policy Act)

Created to encourage co-generation and small power producers, PURPA requires investor owned utilities to purchase electrical power from co-generators or small power producers.

PVC (Polyvinyl Chloride)

The polymerized form of chloroethene or vinyl chloride is a matrix of double the bonded carbon molecule CH2=CHCl. The double bonds break and become single bonds, and the vinyl chloride molecules become bonded to each other. The result is PVC or polyvinyl chloride plastic. The burning of PVC results in the formation of acid rain.

Dictionary Navigation

Citing this page

If you need to cite this page, you can copy this text: