History of the Periodic Table (Chapter 5. 1)

Johann Dobereiner

1817 Grouped elements into TRIADS, based on atomic mass & similar properties.

John Newlands 1863 Law of Octaves – when placed in order of increasing atomic mass, he found that similar properties appeared every 8 elements.

Dimitri MendeleevLothar Meyer(working separately)

1869 Placed elements in order of increasing atomic mass. Credited with creating 1st Periodic Table. Gave us “periodic law.”

Henry Moseley 1913 Arranged table in order of increasing atomic #, based on x-ray experiments. Gave us modern periodic law & table order.

Mendeleev’s Periodic Law

• When elements are arranged by increasing atomic mass, there is a periodic repetition of chemical and physical properties

Moseley’s Periodic Law

• When elements are placed in order of increasing atomic number, there is a periodic repetition of chemical and physical properties

The Periodic Table

The Periodic Table

• Arranged in increasing atomic number

• Columns are called “groups” or “families”

• Columns are numbered 1-18 (new way) or 1-8 with an “A” or “B” designation

• “A” denotes MAIN GROUP, or REPRESENTATIVE, elements

• “B” denotes TRANSITION elements

Classifying the Elements

• Group 1 – Alkali Metals (except H)

• Hydrogen is placed there for e- configuration purposes

Classifying the Elements

• Group 2 – alkaline earth metals

• Both Group 1 & 2 elements are very chemically reactive, reacting with air and water violently.

• Group 1 is the most reactive

Classifying the Elements

• Groups 3-12 (“B” elements) = transition metals and inner transition metals

• Transition metals are in the main body of the table

• Inner transition metals are the lanthanides & actinides

Classifying the Elements

• Groups 13, 14 – a mix of metals & non metals, named for their top element

• Group 13 Boron Group

• Group 14 Carbon Group

• Elements get more metallic as you go down the group

Classifying the Elements

• Groups 15-18 include non- metals (and some metalloids)

• Mixed elements – more metallic as you go down groups; more non-metallic as you move across the periods

Classifying the Elements

• Group 15 –Nitrogen group

Classifying the Elements

• Group 16 – Chalcogens (oxygen group)

Classifying the Elements

• Group 17 -- Halogens

Classifying the Elements

• Group 18 – Noble Gases

• Non-reactive• Full valence shell of 8

e-• s & p sublevels full

Metalloids

• A special group of 8 elements along the “stairstep” line on the periodic table

• Have characteristics of both metals and non metals.

• B, Si, Ge, As, Sb, Te, Po, At

• Si and Ge are known as semiconductors – used in computers and other electronics

Metalloids