Section 2 – pg 131 Organizing the Elements Chapter 4 Section 2 – pg 131 Organizing the Elements

Mendeleev’s Periodic Table Pg 132 Mendeleev’s Periodic Table By 1869 a total of 63 elements had been discovered A Russian scientist, Dmitri Mendeleev, discovered a set of patterns that applied to all the elements

Patterns of Properties Pg 132 Patterns of Properties To find the pattern of the elements Mendeleev wrote each element’s melting point, density, color and atomic mass on individual cards Atomic Mass: the average mass of all the isotopes of an element Mendeleev tried arranging the cards in many ways Mendeleev noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass

Mendeleev published the first periodic table Pg 132 After putting the elements in order by atomic mass, he grouped them together based on other characteristics Mendeleev published the first periodic table A periodic table is an arrangement of elements showing the repeating pattern of their properties

Predicting New Elements Pg 133 Predicting New Elements When arranging the elements by atomic mass, sometimes the elements did not always group similar elements together Mendeleev moved these elements to be in groups of similar properties, leaving three blank spots Mendeleev predicted that these spots would be filled with elements not yet discovered but would have the properties of the groups they fit into Within 16 years, scientists discovered three missing elements that had properties similar to what Mendeleev predicted (scandium, gallium, germanium)

Gallium (69.72) Germanium (72.59) Scandium (44.956)

The Modern Periodic Table Pg 133 The Modern Periodic Table The elements are arranged in order of increasing atomic number (the number of protons) Mendeleev’s arranged by atomic mass The properties of an element can be predicted from its location on the periodic table

Pg 136 Classes of Elements Metals Semimetals Nonmetals Inert Gases

Periods Horizontal rows of the periodic table Each row increases in mass: left to right Total of 7 periods

Groups Pg 136 The vertical columns of the periodic table AKA: family Consists of elements with similar characteristics Group 1: react violently with water Group 2 reacts with water slowly or not at all Group 17: react violently with Group 1 elements Group 18: rarely react at all

Reading the Data Pg 137 Atomic Number (# of protons) Chemical Symbol A representation of an element usually consisting of two letters Element Name Atomic Mass (average mass of all the isotopes)

Chapter 4 Section 2 Homework – pg 137

1A. In what order did Mendeleev arrange the elements in his periodic table?

1B. What pattern did Mendeleev discover when he arranged the elements?

1C. What elements did Mendeleev group with lithium in his periodic table?

2A. What information is listed in an elements square in the periodic table?

2B. Describe two differences between Mendeleev’s periodic table and the modern periodic table.

2C. What element has 47 protons in its nucleus?