Period 5 element

A period 5 element is one of the chemical elements in the fifth row (or period) of the periodic table of the elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.

This period contains technetium, one of the two elements until lead that has no stable isotopes (along with promethium), as well as molybdenum and iodine, two of the heaviest elements with a known biological role, and Niobium has the largest magnetic known penetration depth of all the elements. Zirconium is one of the main components of zircon crystals, currently the oldest known minerals in the earth's crust. Many later transition metals, such as rhodium, are very commonly used in jewelry due to the fact that they are incredibly shiny.

This period is known to have a large number of exceptions to the Madelung rule.

(*) Exception to the Madelung rule

Rubidium is the first element placed in period 5. It is an alkali metal, the most reactive group in the periodic table, having properties and similarities with both other alkali metals and other period 5 elements. For example, rubidium has 5 electron shells, a property found in all other period 5 elements, whereas its electron configuration's ending is similar to all other alkali metals: s¹.Rubidium also follows the trend of increasing reactivity as the atomic number increases in the alkali metals, for it is more reactive than potassium, but less so than caesium. In addition, both potassium and rubidium yield almost the same hue when , so researchers must use different methods to differentiate between these two 1st group elements. Rubidium is very susceptible to oxidation in air, similar to most of the other alkali metals, so it readily transforms into rubidium oxide, a yellow solid with the chemical formula Rb₂O.

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