Chapter 4.2

Organizing the Elements

Page 131

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.

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

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

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!

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!!!

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.

Divisions of the Periodic Table

• The Periodic Table can be broken up into 4 general categories:– The metals– Nonmetals– Inert Gases– Semimetals

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.

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

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)

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

Element name

Chemical Symbol

Atomic Mass