Arranging The Elements Chapter 5 Section 1 pages 106-112

History 101- The Periodic Table Dmitri Mendeleev – Russian Chemist – 1869 Discovered a pattern in the elements His final arrangement – Arrange by increasing atomic mass He left gaps in his table – for yet unknown elements to be discovered and placed. He could predict the properties of the undiscovered elements by looking at the known elements that surrounded the gaps.

Our Current Periodic Table Henry Mosely – British – 1914 Rearranged original table – CURRENT – by atomic number This allowed all elements to fit the pattern

Classification of Elements on the Periodic Table Type: Metal, Nonmetal and Metalloid Number of outer electrons Divided by the “zig-zag” line

Metals Metalloid Nonmetals Left of zig-zag line Few outer electrons Most solid at room temperature Metalloid Border zig-zag line ~ half complete set of outer electrons Nonmetals Right of zig-zag line May be full or almost full of outer electrons More than half are gas at room temperature

Decoding the Elements of the Periodic Table Atomic Number = the number of protons/electrons Symbol 1, 2, or 3 Letter Symbol – First letter is capitalized Name Sometimes named after people or places Atomic Mass Protons + Neutrons

Periods Side to Side – Horizontal (7) Conductivity/Reactivity changes gradually as you move from left to right Period Number = Number of energy Levels 1st Period = 1 Shell 2nd Period = 2 Shells 3rd Period = 3 Shells 4th Period = 4 Shells

Groups (Sometimes called Families) Up and Down – Vertical (18) Each group has similar physical and chemical properties If you know the group number, you can determine the number of outer electrons. Group 18 = 8 electrons Group 1 = 1 electron Except for He, it has 2 electrons Group 2 = 2 electrons The electrons in the outer shell are called “valence” electrons