The Russian chemist Dmitri Mendeleev uncovered evidence that consisted ot a huge collection at acts about the 63 elements that had been discovered by the mid-1500’s. His clues had to do with the physical and chemical properties ot these elements. Mendeleev was convinced dtat he could arrange the elements so that those with similar properties were grouped together. Mendeleev made a card or each element including the atomic mass, density, color, and melting point. He also included the element’s valence, hunding power. Mendeteev, looking tor pattems, arranged the card so that the atomic mass increases, lt he staned with lithium, the next would be beryllium. Lett would come boron. carbon, nitrogen, oxygen, and fluorine with the cards arranged in this order Mundeteev noticed that the pattern of valences was.
Seven elements in a row and a pattern at valences repeating themselves. As he arranged all 63 cards in this manner tn doing so he also saw something even more remarkable. when the elements were arranged in this way, they tell into columns, one under the other. All the elements in one column had the same valence anti showed similar physical and chemical properties. Mendeleev designed a periodic table in which the elements were arranged in order ot increasing atomic mass. The periodic law states that the physical and chemical properties at the elements are periodic functions at their atomic numbers. The periodic table or the elements is one of the most imponant tools ot a scientist, especially a chemist. The periodic table is a classification system. a way ol organizing vast amounts at the information in a logical , usable, meaningtut way, The columns the elements are placed in are called groups or families, Elements within the group have similar but not identical properties. For example, lithium sodium ( Na ), potassium ( K ), and other members or [amily t are all sort. while. shiny metals.
They are all highly reactive elements, wich means they readily combine with other elements to torm compounds, In each individual square it contains the atomic mass, atomic number, chemical symbols and name/abbr, There are now elements ill the periodic table. Most ol the elements are metals. Chemical properties in metals are such things as lust and shininess. Must metals also allow heat and electricity to move through them easily. Therefore metals are good conductors oi heat and electricity. In general metals have high density. This means they are heavy for their Sill There are two other physical properties that are common to many metals. Most metals are ductile, with means they can be drawn out into Iititt wires. And most metals are malleable, with means they can be hammered into thin sheets. The chemical properties oi metals are not as easily observed as the physical propentes.
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The chemical properties of any element depend of the electron arrangement in the atoms or the element. An atom oi a metal can have 1, Z, 3, or 4 electrons in its outermost energy level. The electrons in a metals outermost energy level are held together weakly. So metals are elements that tend to lose their outermost energy levels electrons when they combine chemically. Because they tend to lose electrons, most metals will react chemically with water or oxygen in the atmosphere, this usually results in corrosion. Corrosion is the gradual wearing away or a metal due to a chemical reaction in which the metal element is changed into a metallic compound. Tarnishing is a mutter example of corrosion.
This results when silver reacts with stiller in the air or in certain loads. Properties of nonmetals have no luster and are dull in appearance. Nonmelals do not conduct heat and electricity very well. Nunmetals are brillle and break easily, They Cannill be drawn out inlu wire or hammered into thin sheets. Nonmetals are neither ductile nnr malleable, Nuttmelals usually have lower melting points and densities than that of metals. Nonmelals are not easy to recognize as a group as metals are. Atoms or most nonmetdls are 5. e, 7, or a electrons in the outermost energy level. Atoms with 5, 6. or 7 elections gain 3. 2, or I electron, respectively when they combine chemically. Nunrneldls are elements that tend to gain electrons. When you look at the dividing line between metals and nonmetal you see the melalloids. Metalloid means metallike. All melalluitls are solid lhdl can be slIilIy or dull. They conducl heat and electricity better than nonmetals but not as well as metals. Metalloids are ductile and malleable, the metalloids include boron, silicon, germanium, arsenic, antimony, lellurium, polonium, and astatine.
Chemical lamilies are elements that have similar propenies because they have the same number of valence electrons. The elements in tamily one are called the alkali metals, with the exception oi hydrogen. The alkali melals are soft, siver»whlte, shiny metals. They are so soft they can be cut wilh a knlle. Alkali metals are good conductors or heat and electri ty. The reaction is violent when the alkali metals combine with water and oxygen. Family two consists ol the alkali—earth metals. fliese metals are never lound in nature as uncombined metals. Instead they exist bonded with other metals as compounds. Another ltind ol metal that is hard ln label into a group or lamily is the transition metals. Transition metals have properties similar to other metals. Transition metals are good conductors ol electicity as well. An interesting transition metal is mercury.
Murcuy is a liquid metal at temperatures above -35 degrees celcius. Most transition metals have 1 or 2 valence electrons. When they combine wilh or atoms, they lose either i or both ot their valence electrons, the compounds of transition meteals are usually brightly colored and are oiten used to color paint. To the right at the transition elements are six lamilies, live at them contain some melalloids. Family thirteen is the boron iamily. Atoms oi this tamily usually have three valence electrons. Family iourteen, the carbon family usually have tour valence electrons. The nitrogen family, lamily titteen, is named alter an element that makes up 79% at the air around you: nitrogen. The atoms ol elemenls in Ihis lamily have 5 valence electrons in their outemmsl energy level. These alums lend to share electrons when they bond with other alums. The elemenls that make up Iamlly sixteen are called the oxygen family.
Atoms tll these elements have six valence elections. Most elements in this family share elections when lorming molds. Farm y seventeen is the halogen family. The elements or this lantily have seven yalente elections, Atnnts at these elements only need to gain one elecu’un Iu [ill their outermost energy level. The last tamily. the noble gases. are normally unreaettve. Under special eondttions, tenain nuhle gases t-an tonthine their-ally‘ other elements. Because they du not readily lorm Luntpuunds with other elemenls, the nohle gases are sometimes t-alletl the inen . gases. Certain properties or elements vary itt regular ways lrttm left lu right across a period. These properties include electron arrangement. reattivitv atumie aim, and metallit- urouenies. The yalenee number of an elements is related to the electrons in the uuner most energy level ut an atom ut that element it is these electrons that are involved in the chemical combining Lt! element to [arm compounds.
