(Chapter 18.3)

 

Elements are arranged in the periodic table by increasing atomic number

· 1800’s—Mendeleev  arranged the first periodic table based on atomic mass

· 1913—Moseley arranged atoms by increasing atomic number

Groups—vertical columns in the table: elements have similar properties

·       Elements in the same group have the same number of electrons in

their outer energy level

·       Each energy level can have a maximum number of electrons

o     Energy level 1 can have at most two electrons

o     Energy level 2 can have at most eight electrons

·       Each row ends when an outer energy level is filled

·       Electron dot diagrams use the element symbol and dots to represent outer energy level electrons

Na●                            K●                        Ca:          Mg:

Periods—horizontal rows of elements that contain increasing numbers of protons and electrons

·       Elements are classified as metals, nonmetals, or metalloids (semimetals)

·       Elements are synthesized in laboratories all over the world

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The same elements exist all over the universe

·       Hydrogen and helium are the building blocks of other naturally occurring elements

·       Supernovas spread heavier elements throughout the universe