History of the Periodic TableDuring the nineteenth century, chemists

began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.

Johann Dobereiner 1780-1848Model of Triads

In 1829, he classified some elements into groups of three, which he called triads.

The elements in a triad had similar chemical properties and orderly physical properties. ex. Cl, Br, I and Ca, Sr, Ba

John Newlands 1838-1898Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element

Li         Be            B            C            N            O            F Na       Mg           Al           Si           P            S           

Cl         K         Ca

Rows of elements had seven elements and the eighth fell under the first element. The number of elements known were very limited and no elements from the noble or inert gas elements such as helium, neon, argon, etc. were known.

Newlands' claim to see a repeating pattern was met with savage ridicule. He was told his classification was as arbitrary as putting them in alphabetical order.

Look again…Li         Be            B            C            N           

O            F Na       Mg           Al           Si           P           

S            Cl         K         Ca

Was Newlands totally out to lunch?Why did the rule of octaves fail as a means of

organizing elements? It is not valid for elements that had atomic masses

higher than Ca. When more elements were discovered, such as elements

from the noble gases such as He, Ne, Ar, they could not be accommodated in his table.

Dmitri Mendeleev 1832-1907The Father of the Modern Periodic Table

Russian ChemistIn 1869 he

published the a table of the elements in order of increasing atomic mass.

Early version of the periodic table from Mendeleev’s journal.

Lothar Meyer 1830-1895At the same time, he published his own

table of the elements organized by increasing atomic mass.

•Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass.

•Both left vacant spaces where unknown elements should fit.

•So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?

Mendeleev…stated that if the atomic weight of an element

caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)

was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.

After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined.

By looking at our modern periodic table, can you identify what problems might have caused chemists a headache?

Ar and KCo and NiTe and ITh and P

Henry Mosely 1887-1915In 1913, through his work with X-rays, he determined

the atomic number (nuclear charge) of the elements.“There is in the atom a fundamental quantity which

increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus”

He rearranged the elements in order of increasing atomic number.

He was killed during WWI in Gallipoli by a sniper’s bullet at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

The Modern Periodic TableThe work and collaboration of scientists

around the world has led to the development of the most important tool in chemistry today.

From the periodic table we are able to predict the chemical and physical properties of the elements.

The Periodic TableThe modern periodic table contains 117

elements. (1-116, 118 as of July 2009)

The Periodic Law states: When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Organization of the Periodic TableThe periodic table organized by atomic number is

divided into groups, families and periods.Groups: Columns of elements with the same number

of valence electrons. (ex. Group one has 1 valence electron)

Families: One or more groups that have similar properties.( Alkali metals, transition metals, halogens etc)

Periods: Horizontal rows of elements. The period number of an element signifies the highest unexcited energy level for an electron in that element.

The Periodic Table

The Element Song: http://www.youtube.com/watch?v=GFIvXVMbII0&feature=related

Notes…Use this page to

label and make notes about chemical families

Number groups 1 – 18

Separate Metals and Non-metals

Alkali Metals

Noble Gases

Halogens

Alkaline Earth Metals

Transition Metals

Group 1 – Alkali MetalsLi, Na, K, Rb, Cs, FrHighly reactive metals that do not occur

freely in natureSilver coloured, soft, low density metalsValence shell has one electronTendency to lose one electron to form +1 ionAlkali metals react violently with water to

give off hydrogen gas Reactivity increases down the group

Reaction of Alkali Metals

Source: http://www.youtube.com/watch?v=uixxJtJPVXkAnother version: http://www.youtube.com/watch?v=m55kgyApYrY

Group 2 – Alkaline Earth MetalsBe, Mg, Ca, Sr, Ba, RaReactive Silver colored, soft metalsHave 2 electrons in valence shell.Form +2 ionsNot found in elemental form in nature, but

often as compounds in a variety of rock types.Reactivity increases down the group

Group 2 – Alkaline Earth Metals

Group 3-12 – Transition MetalsThe 38 elements in groups 3 through 12 . As with all metals, the transition metals are

both ductile and malleable, and conduct electricity and heat.

Transition metals often more than one possible ion charge – Multivalent.

Three noteworthy elements in the transition metals family are iron, cobalt, and nickel, the only elements known to produce a magnetic field.

Group 17 - HalogensThe only group which contains elements in all

three states of matter. (Gas: F, Cl. Liquid: Br, Solid: I)

Highly reactive7 electrons in the valence shellHighly electronegative – attract one electron

to to form -1 ionExist as salts (halides) or as diatomic

moleculesReactivity decreases down the group

Group 17 - Halogens

Source: http://openlearn.open.ac.uk/file.php/3561/s205_2_003v.mp4

Group 18 – Noble GasesAll gases at room temperatureNon-reactive (inert)Have a full valence shellExist in a monatomic state

The noble gases glow brightly when an electric discharge is passed through them, and so are used as advertising signs: neon tubes glow red, xenon blue, and krypton bluish-white; argon tubes glow pale red at low pressures, blue at high pressures.

http://www.youtube.com/watch?v=QLrofyj6a2s&feature=related