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The Periodic Table Objective 3: Lesson 10 Notes Patterns ! Dmitri Mendeleev was a Russian chemist that classified elements by their properties The Periodic Table ! Atomic mass is the total number of protons and neutrons in the nucleus of atoms ! Mendeleev arranged elements by atomic mass and then found that many of the elements with the same properties ended up in same column ! Developed the periodic table Periods and Groups ! Periods are the horizontal rows ( 1-‐7), have the same number of energy levels ! Groups are the vertical columns ( 1-‐18), have the same chemical properties and same # of valence electrons Metals ! More than 75% of elements in the periodic table are metals ! Found to the left of the “staircase” on the periodic table (exception H is not a metal) ! Most metals: ! Shiny/have luster ! Malleable – can be beaten or rolled into thin sheets ! Ductile-‐ can be stretched into wires ! Solid at room temp ( not Mercury) ! Good conductors of heat and electricity Nonmetals ! Found to the right of the “staircase” on the periodic table (EXCEPTION = HYDROGEN) ! Most nonmetals: ! ! ! ! Dull Brittle Most are gases at room temp Poor conductors of electricity and heat Semimetals/Metalloids ! Found along the border of the “staircase” on the periodic table ! Share characteristics of metals and nonmetals Valence Electrons ! The electrons in the outer most energy level of the atom ! Allow atoms to form chemical bonds with other atoms ! All elements in the same group ( column) have similar chemical properties ! Hydrogen (H) is a gas, not a metal, in Group 1 because it has 1 valence electron
