Unveiling the Periodic Table: Mendeleev's Discovery and Modern Structure

1. Chapter 4.2 Organizing the Elements Page 131

2. The 1st Periodic Table • In 1869, there were 63 known elements. • These included a few gases, 2 liquids and the rest solids. • Some reacted very violently and some reacted very slowly. • A Russian Scientist, Dmitri Mendeleev, discovered that there were patterns that applied to all of the elements. He arranged them in a table, the periodic table of elements.

3. The Periodic Table Dimitri Ivanovich Mendeleev (1834-1907) • Born in Siberia the youngest of 17 children! • Refused admission to the university • Became a school teacher • Loved to play Patience, a card game like solitaire

4. The Periodic Table • He began to group elements that had similar chemical and physical properties • Then grouped according to atomic mass and bonding power • Saw patterns among the elements

5. Mendeleev’s Discoveries • He knew that some elements have similar chemical and physical properties and thought that these similar properties were the secrets to a hidden pattern. • To discover this pattern, Mendeleev wrote down each element’s melting point, density, atomic mass and color on individual cards. • When arranging the cards in various ways, Mendeleev noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass. • Group by group, this arrangement became known as the 1st periodic table!

6. Predicting New Elements… • After arranging the 63 known elements there were 3 blank spaces. • These spaces were elements that had not yet been discovered and he was even able to predict these unknown elements’ chemical and physical properties! WOW!!!

7. The Modern Periodic Table • Since Mendeleev’s 1st periodic table, the modern periodic table contains more than 100 elements. • In the modern periodic table, the elements are arranged in order of increasing atomic number. • The properties of an element can be predicted from its location on the periodic table.

8. Divisions of the Periodic Table • The Periodic Table can be broken up into 4 general categories: • The metals • Nonmetals • Inert Gases • Semimetals

9. The Periods in the Periodic Table… • Periods: The periodic table is organized into horizontal rows called periods. • Periods contain a series of different elements • The periodic table contains 7 periods – the number of electron levels • Period 1 has 2 elements • Periods 2 and 3 each have 8 elements • Periods 4 and 5 have 18 elements • Period 6 has 32 elements • Periods 6 and 7 are placed off the table to save space and are known as the lantahnides and actinides.

10. Periods Cont. • From Left to Right the elements change in a predictable pattern: • Metals are located on the left where as nonmetals are located on the right. • Atoms increase in mass from left to right • Atoms increase in size from top to bottom, but decrease in size from left to right

11. The Groups in the Periodic Table… • The vertical columns of the periodic table are called groups (or families). • Groups are also known as “families” (groups of elements with similar characteristics) • Patterns can also be predicted from groups. • Examples: • Each element in each group contains the same number of valence electron (the number of electrons in the outer most energy level) • Each family of elements generally reacts the same with other groups (all group 1 elements react very violently with group 17 elements)

13. Reading the Periodic Table • Each square in the periodic table contains lots of information. In your textbook it contains 4 pieces of information: • An element’s atomic number • An element’s chemical symbol • This is a representation of an element, consists of 1 or 2 letters. • An element’s name • An element’s atomic mass. Atomic number Chemical Symbol Element name Atomic Mass