Lead is a Block P, Group 14, Period 6 element. The number of electrons in each of Lead's shells is 2, 8, 18, 32, 18, 4 and its electronic configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p². In its elemental form lead's CAS number is 7439-92-1. The lead atom has a radius of 175.pm and it's Van der Waals radius is 202.pm. Lead and its compounds are poisonous. Lead is a bluish-white metal of bright luster, naturally occurring as a mixture of four stable isotopes: 204Pb (1.48%), 206Pb (23.6%), 207Pb (22.6%), and 208Pb (52.3%). It is highly resistant to corrosion and can be used to contain corrosive liquids such as sulfuric acid. Great quantities of Lead, both as the dioxide and the metal, are used in batteries, cable covering, plumbing, and ammunition. Alloys include solder, type metal, and various antifriction metals and compounds. Lead is extremely effective at absorbing sound and vibration. It is also used as radiation shielding for X-ray equipment and nuclear reactors. Oxides of Lead are used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. Lead ceramics and crystalline material have a wide range of industrial and optical applications, including infrared detection and imaging. Lead-based semiconductors, such as lead telluride, lead selenide and lead antimonide are finding application in photovoltaic (solar energy) cells and infra red detectors. Lead was first discovered by Early Man. The origin of the name Lithium comes from the Greek word protos meaning "first". See Lead research below.

Selenium is a Block P, Group 16, Period 4 element. The number of electrons in each of Selenium's shells is 2, 8, 18, 6 and its electronic configuration is [Ar] 3d¹⁰ 4s² 4p⁴. In its elemental form selenium's CAS number is 7782-49-2. The selenium atom has a radius of 116.pm and it's Van der Waals radius is 190.pm. The EPA does not classify selenium as carcinogenic, although selenium sulfide is a probable carcinogen. Selenates and selenites which are compounds of selenium, are highly toxic. Hydrogen selenide gas (SeH2) is the most acutely toxic compound of selenium. Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. of photocells and exposure meters for photographic use, as well as solar cells. Below its melting point, selenium is a p-type semiconductor and has many uses in electronic and solid-state applications. Selenium is available as metal and compounds with purities from 99% to 99.9999% (ACS grade to ultra-high purity); metals in the form of foil, sputtering target, and rod, and compounds as submicron and nanopowder. Selenium was first discovered by Jons Berzelius in 1817. The origin of the name Selenium comes from the Greek word "Selênê" meaning moon. See selenium research below.