Properties of metals, metalloids and nonmetals one or two properties very different from the expected norm, or that are otherwise notable. Sodium, potassium, rubidium, caesium, barium, platinum, gold Manganese Iron, cobalt, nickel, gadolinium, terbium, dysprosium, holmium, erbium, thulium Iridium Gold Mercury Lead Bismuth Uranium Plutonium Boron Boron, antimony Silicon Arsenic Antimony Hydrogen Helium Carbon Phosphorus Iodine Properties of metals, metalloids and nonmetals Metals appear lustrous (beneath any patina); form mixtures (alloys) when combined with other metals; tend to lose or share electrons when they react with other substances; and each forms at least one predominantly basic oxide. Most metals are silvery looking, high density, relatively soft
Arsenic pentachloride more stable and the instability of AsCl appears anomalous. The cause is believed to be due to incomplete shielding of the nucleus in the elements following the first transition series (i.e. gallium, germanium, arsenic, selenium, bromine, and krypton) which leads to stabilisation of their 4s electrons making them less available for bonding. This effect has been termed the d-block contraction and is similar to the f-block contraction normally termed the lanthanide contraction. Arsenic pentachloride Arsenic pentachloride is a chemical compound of arsenic and chlorine. This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride, AsCl, in