![]() Group 17: The Halogens – fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) are nonmetals.In contrast, calcium and magnesium are the fifth and sixth most abundant elements on Earth, respectively they are found in huge deposits of limestone and other minerals. Beryllium, strontium, and barium are rare, and radium is unstable and highly radioactive. Group 2: The Alkaline Earth Metals – beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) are shiny, slivery-white, somewhat reactive metals.Hydrogen is unique in that it is generally placed in Group 1, but it is not a metal. ![]() Although lithium, rubidium, and cesium are relatively rare in nature, and francium is so unstable and highly radioactive that it exists in only trace amounts, sodium and potassium are the seventh and eighth most abundant elements in Earth’s crust, respectively. One example is table salt (sodium chloride) lithium compounds are used in greases, in batteries, and as drugs to treat patients who exhibit manic-depressive, or bipolar, behavior. The compounds of the alkali metals are common in nature and daily life. Group 1: The Alkali Metals – lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) are soft, shiny, and highly reactive metals.For example, the elements of Group 1 are known as the alkali metals, Group 2 are the alkaline earth metals, Group 17 are the halogens, and Group 18 are the noble gases. Chemists often make general statements about the properties of the elements in a group using descriptive names with historical origins. The periodic table is arranged so that elements with similar chemical behaviors are in the same group. The trends of the atomic radii and melting points (and other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom discussed in the following sections.
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