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Probing the Periodic Table History of the Periodic Table • Elements are the basic building blocks of all things. • Elements are made of atoms, They are small, but they have mass too. • The atomic mass of an element is the weight of one atom of the element. History of the Periodic Table • In 1869, Dmitri Mendeleev listed all the elements known at the time in order of their atomic weight. He arranged the list into a table of rows and columns. • In Mendeleev’s day, there were 63 known elements. Today, we know of almost 100 elements that can be found in nature. Describe the Periodic Table Describe the Periodic Table • The periodic table is a chemistry reference • It arranges all the known elements in an informative grid Describe the Periodic Table • Elements are arranged left to right and top to bottom in order of increasing atomic number • This order usually coincides with increasing atomic mass Describe the Periodic Table • The Table's pattern and arrangement shows the arrangement of electrons in the atom. • Elements have different atomic numbers - the number of protons or electrons increases up the table as electrons fill the shells (orbit levels). Describe the Periodic Table Elements have different atomic masses the number of protons plus neutrons increases up the table. • Rows - elements of each row have the same number of orbit levels (shells). • Columns - elements have the same number of electrons in the outermost energy level or shell (one to eight). Describe the Periodic Table • The different rows of elements are called periods. – The period number of an element signifies the highest energy level an electron in that element occupies • The different columns of elements are called groups or families – Elements in the same family have similar properties Describe the Periodic Table Describe How To Read The Periodic Table Describe how to read the periodic table: • Every table has: Describe how to read the periodic table: Atomic Number The number of protons in an atom identifies the element. The number of protons in an atom is referred to as the atomic number of that element. Describe how to read the periodic table: Atomic Symbol: The atomic symbol is one or two letters chosen to represent an element ("H" for "hydrogen," etc.). These symbols are used every where in the world Usually, a symbol is the abbreviation of the element or the abbreviated Latin name of the element. Describe how to read the periodic table: Atomic Mass: The atomic mass is the average mass of an element in atomic mass units ("amu"). Though individual atoms always have a whole number of amu’s, the atomic mass on the periodic table is shown as a decimal number because it is an average of all the isotopes of an element.