The Periodic Table and the Elements
The periodic table of the chemical elements is a list of known Elements. Elements are substances that consist of only one type of atom. In the table, the elements are placed in the order of their atomic numbers starting with the lowest number. The atomic number of an element is the same as the number of protons in that particular atom.In the periodic table the elements are arranged into periods and groups. A row of elements across the table is called a period. Each period has a number: from 1 to 8. Period 1 has only 2 elements in it: hydrogen and helium. Period 2 and Period 3 both have 8 elements. Other periods are longer. Elements in a period have consecutive atomic numbers. A column of elements down the table is called a group. There are 18 groups in the standard periodic table. Each group has a number: from 1 to 18. Elements in a group have electrons arranged in similar ways, which gives them similar chemical properties (they behave in similar ways). For example, group 18 is known as the noble gases because they are all gases and they do not combine with other atoms. There are two systems of group numbers; one using Arabic numerals (1,2,3) and the other two using Roman numerals (I, II, III). The Periodic Table was invented and arranged by the Russian chemist Dmitry Ivanovich Mendeleyev (1834-1907). In his honour, element 101 was named after him, Mendelevium.
Metals and Non-Metals
All Metals are located on the left-hand side of the Periodic Table. They are solid at room temperature (except Mercury) and are malleable, shiny, and good electricity conductors. All Non-Metals are located on the right-hand side of the table (except Hydrogen) and do not meet any of the conditions above to be considered a metal. Between the Metals and Non-Metals are the Metalloids, which meet only some of the conditions to be considered a metal.
Alkali Metals are the elements in the first group of the table. Alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements.
Alkaline Earth Metals
Alkaline Earth Metals are similar to Alkali Metals, but less reactive. They do not react furiously with air. The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure. They also have full outer electron shells.
Many scientists describe a «transition metal» as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. Most of them, like Gold, Silver, Nickel, and Copper, are used in everyday things, like coins.
Halogens are the elements of the 17th group. They are gases at room temperature. Pure halogens, like Bromine, Chlorine, and Florine, are poisonous.
These are the elements of the furthest left-hand side group. They do not form molecules and compounds with other atoms, which is why you might have never heard of Helium compounds. They include Helium, the second element, Neon, and Krypton. Noble Gases are used in many everyday objects.
The lanthanide (or lanthanoid) series is a group of 15 elements that have atomic numbers 57 to 71. This group starts at Lanthanum (the element it is named after) and it ends at Lutetium. They are Rare Earth metals and have properties similar to the Alkaline Earth metals.
Actinides are the elements in the period below the Lanthanides, and starts at number 89 and ends at 103. The group is named after the first group in the series, Actinium. They all are radioactive and 9 of them are not found naturally. It was believed that Uranium was the heaviest element that could be found naturally, and attempts to make an even heavier element (Plutonium) manually succeeded. However, Plutonium was discovered naturally in a sample of pitchblende ore in 1941.