Discovering a Pattern • Dmitri Mendeleev- Russian Chemist- discovered a pattern to the element in 1869 • First he arranged them by different properties (density, appearance, MP). • After much thought he arranged them in order of increasing atomic mass. • When he did that a pattern appeared!!!!
Periodic Properties of the Elements • When arranged in order of increasing atomic mass, those that had similar properties occurred in a repeating pattern. • Periodic-happening at regular intervals • Mendeleev found that the elements properties followed a pattern that repeated every 7 elements.
Predicting Properties of Missing Elements • Mendeleev predicted that elements yet to be found would fill in the gaps of the pattern • He used the pattern to predict their properties • By 1886 all the gaps had been filled and his predictions were correct!
Changing the Arrangement • A few elements did not fit the pattern in Mendeleev’s table • Mendeleev thought if he found a more accurate atomic mass than he would fix the flaws in his table. But his masses were correct. • Henry Moseley-determined the # of protons-the atomic #- • All elements fit the pattern in the table when arranged buy atomic #. • Periodic Law- repeating chem. & phys. Properties of elements change periodically with the elements atomic #
Metals • Most Elements • Found LEFT of the zigzag line on the table • Few electrons in their outer energy level • Most are solid at room temp. Mercury is an exception-It is liquid at room temp. • Shiny • Ductile-drawn into thin wires • Good conductors of electric current • Good conductors of thermal energy • Malleable- flattened with a hammer and won’t shatter
Nonmetals • Found right of the zigzag line on the table • Almost a complete set of electrons in their outer level. • Atoms of the elements in Group 18 (noble gases)-have a complete set of electrons • More than ½ are gases at room temp. • Many properties of nonmetals are opposite of metal properties • Not malleable or ductile, not shiny, poor conductors of thermal energy and electric current
Metalloids • Can also be called semiconductors. • These border the zigzag line on the table. • About ½ have a complete set of electrons in their outer energy level • Have properties of both metals and nonmetals • Ex: Tellurium is shiny BUT it is brittle • Ex: Boron-very hard but also very brittle, at high temps. It is a good conductor of electric current
Chemical Symbols • Each element is identified by a chemical symbol. Symbols are worldwide. • Some elements are named after scientists, some are named after places. Some names may vary by country. • One or two letters. The first letter is always capitalized. • Newest elements have temporary three letter symbols
Rows And Columns • Horizontal rows (from left to right) are called PERIODS • Physical and Chemical Properties in a row follow a periodic pattern as you move across. • Conductivity and reactivity change gradually as you move left to right
Rows And Columns • Vertical columns (top to bottom) are called GROUPS • Elements in the same group often have similar chemical and physical properties. • A group is also called a FAMILY