Discovering a Pattern Dmitri Mendeleev- Russian Chemist- discovered a pattern to the element in 1869 Dmitri Mendeleev- Russian Chemist- discovered a pattern to the element in 1869 First he arranged them by different properties (density, appearance, MP). First he arranged them by different properties (density, appearance, MP). After much thought he arranged them in order of increasing atomic mass. After much thought he arranged them in order of increasing atomic mass. When he did that a pattern appeared!!!! 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. When arranged in order of increasing atomic mass, those that had similar properties occurred in a repeating pattern. Periodic-happening at regular intervals Periodic-happening at regular intervals Mendeleev found that the elements properties followed a pattern that repeated every 7 elements. 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 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. 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 #- Henry Moseley-determined the # of protons-the atomic #- All elements fit the pattern in the table when arranged buy 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 # Periodic Law- repeating chem. & phys. Properties of elements change periodically with the elements atomic #

Metals 1. Most Elements 2. Found LEFT of the zigzag line on the table 3. Few electrons in their outer energy level 4. Most are solid at room temp. Mercury is an exception-It is liquid at room temp. 5. Shiny 6. Ductile-drawn into thin wires 7. Good conductors of electric current 8. Good conductors of thermal energy 9. 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 The more you go to the left, the more the element becomes conductive and reactive

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