The Periodic Table

The Periodic Table A few elements, including copper, silver, and gold, have been known for thousands of years There were only 13 elements identified by the year 1700. Chemists suspected that other elements existed. As chemists began to use scientific methods to search for elements, the rate of discovery increased.

The Periodic Table Early chemists attempted to organize the known elements Some used the properties of the elements

Dobereiner was a German chemist who published his classification of the elements He organized the elements into triads

The Periodic Table In 1869, a Russian chemist and teacher, Dmitri Mendeleev, published a table of the elements. The organization he chose was a periodic table. Elements in a periodic table are arranged into groups based on a set of repeating properties. This concept is known as periodicity.

The Periodic Table  Mendeleev left spaces in his table  He predicted that elements would be discovered to fill those spaces, and he predicted what their properties would be based on their location in the table.

The Periodic Table Mendeleev’s table was so successful because chemists were able to make predictions from it. However his table had one error It was arranged by increasing atomic mass.

The Periodic Table  Henry Moseley modified Mendeleev’s table

He arranged the elements by increasing atomic number. Elements that have similar chemical and physical properties end up in the same column in the periodic table.

 This led to the Periodic Law

The physical and chemical properties of elements are periodic functions of their atomic numbers.

The Periodic Table Although Mendeleev’s table only had 60 elements, today’s table has 118 elements Many elements have been discovered since his original work The noble gases - due to their unreactivity The lanthanides and actinides series – many are man-made

The Periodic Table There are seven horizontal rows or periods in the table Each period corresponds to the energy level

There are eighteen vertical columns or groups in the table

The Periodic Table The elements can be grouped into three broad classes based on their general properties: Metals Nonmetals Metalloids

The Periodic Table The majority of elements are metals Metals have three key properties Shiny or luster Flexible (malleable and ductile) Good conductor of energy

The Periodic Table Although there are fewer nonmetals, they are more abundant on Earth Nonmetals have three key properties Dull Brittle Poor conductor of energy

The Periodic Table Metalloids have properties of metals and nonmetals Their properties can be changed by conditions

They are found along the stair step of the periodic table Silicon is the most famous metalloid It is responsible for computer chips

The Periodic Table Remember: s block – groups 1 & 2 p block – groups 13 – 18 d block – groups 3 – 12 f block – bottom two rows

s & p block elements are called main group (representative) elements

The Periodic Table s block Group 1 – Alkali metals (s1) Most reactive metals So reactive, not found in nature as elements 1 valence electron

Group 2 – Alkaline Earth metals (s2) Less reactive than group 1 metals 2 valence electrons

The Periodic Table p block Group 13 – Mixed group (s2p1) Even less reactive than groups 1 & 2 3 valence electrons

Group 14 – Mixed group (s2p2) 4 valence electrons

Group 15 – Mixed group (s2p3) 5 valence electrons

The Periodic Table p block Group 16 – Nonmetals (s2p4) 6 valence electrons

Group 17 – Halogens (s2p5) Most reactive nonmetals 7 valence electrons

Group 18 – Noble Gases (s2p6) 8 valence electrons (with the exception of helium) Completely unreactive nonmetals

The Periodic Table d block Groups 3 – 12 – Transition metals  Less reactive than groups 1 & 2  Have the ability to move their electrons from s and d orbitals

f block Bottom two rows  Known as the lanthanides and actinides (inner transition metals or rare earth metals)  Have the ability to move their electrons from s and f orbitals

The Periodic Table Valence electrons are the electrons found in the outermost energy level These are the electrons available to be gained, lost, or shared All atoms want 8 valence electrons or a full outer energy level Noble gas electron configuration

Valence electrons determine the chemical properties of the atom Valence electrons can be represented using Lewis Dot Diagrams

The Periodic Table Atoms are neutral because there are equal numbers of both protons and electrons Sometimes atoms can gain or lose electrons to form ions An ion is an atom or group of atoms that has a positive or negative charge

Losing electrons results in a positive ion called a cation Gaining electrons results in a negative ion called an anion